PHYS 141/121 Mechanics Video Projects

Videos for 141 Fall 2018

Title: Inverse Square Law, Names: Brenden Billing, Holly Anderson, Reagan Lawson, Jackie Jacobson, Description: this video is showing and explaining the concept behind the inverse square law and demonstrating its real life applications. This is a well-done video. However, it didn’t address mechanics. As is now, it receives a “B”. For an “A”, please submit a calculation… How far from the earth’s center do we put our geosynchronous orbits? That is, the satellites that orbit the earth in exactly one day, so they stay above the same spot? Please do this calculation using the inverse square law. Thanks!

  OK, that is good. Your grade is now “A”

Sarah B, Ryan D, Komal M., Josh R. In this project, our experiment involved pushing Sarah down a hallway. We analyzed the forces and torques applied to Sarah and Ryan to find the dynamic coefficient of friction between the sheet Sarah was on and the tile as well as the static coefficient of friction between Ryan’s shoes and the tile.Link:
This is a good video. The only thing that is worth improving is adding a recognition that the friction on Sarah is dynamic friction = uN, but the friction of Ryan’s shoes is static friction which is < or = uN. Thus, they may have had the same coefficient of friction on them, but Ryan didn’t “use the full coefficient of friction” because he is heavier and has a greater normal force. You have an “A-“ at present. For an “A”, please submit a document to me explaining this correction.

Very good, you have an “A” now

  1. Mac Gray, Tanvi Kharkar, Christian Rudnick, Rachel Staude: Our group would like to recreate the video titled “system of masses using dynamics”.:  I found this to be an excellently explained video. However, there were no measurements/activity involved. You have a “B”. For an “A”, please take some measurements and submit a document to me with the results. Atwood MachineOK, this is great. Your grade is now an “A”.

Names: Dimitri Charitou, Alek Ramirez, Micah Jeffries, Sabian Jackson:  “Calculating the Elevation of an Egg Under a Stretched Spring”  We will attach a weight to a spring that is hanging above an egg.  The height of the spring is placed at an arbitrary location.  From there, we will calculate the spring constant, the weight’s total energy, and the elevation we must raise the egg in order for the weight to touch, but not crack, the egg. Words…. You say “we multiply the weight in kg by the force of gravity, 10 m/s^2″. Please correct this or write out for me how this should be and be more careful in the future! Also, “K” is not unitless… what are the units? 
This was a well done video in my opinion. However, I’m very confused. It seems you are saying that you drop a mass on a spring from the height determined by the spring’s relaxed (unstretched) position and where does it stop?… right? Your equations provides two answers: dx = 0 and dx = 2mg/k, or twice the extension that you get if you let the mass hang on the spring in equilibrium… which is about 60 cm. That’s where my understanding ends.
Then it seems you subtract this value from 63 cm and get an answer of 3.4 cm, but you change it to 34 cm… where did this 63 cm come from?
Your correct experiment likely is a coincidence because 34 cm is about half of the 60 cm that you calculated. So if you hung the mass on the stretched spring 34 cm and then raised the mass to the relaxed spring height (about 68 cm above the egg) and dropped it, the mass should come very close… but I’m only guessing.  . …. after correcting the video:  think your measurements at 42 seconds is incorrect. This time, you’ve divided by 10 for 63 cm and 59.6 cm… if your calculations at 4:03 are correct. Grade is now an A because I understand what you were doing.

Title of Video: Tension in a Conical Pendulum
Names: Jennifer Maunder, Brandon Lyday, Brittani Kealoha, Marce Dean
Description: We create a conical pendulum and find the tension in the string of the pendulum.
url: (let me know if that url doesn’t work and I’ll send a new one)
Excellent professional video. Two major problems, and I ask that you correct the video if you could, so I can use it in the future:
You used the wrong omega… instead you used frequency. You should see from the picture that the force of gravity is about the same as the sum of the forces (= ma), yet you got a very different value. The acceleration should be much closer to that of gravity. Please correct this.  Presently you have a “B”. Do what I ask and you will have an “A”. After making corrections for this video it is better: This makes sense to me now. Does it seem more reasonable to you too? Your answers had way way way too many significant figures on them. Your measurements are not near that accurate. Now your grade is an “A

Philip Schremp, Scott Martin, Max Webb: Physics of a screw.
You’ve correctly calculated the mechanical advantage of the screw. However, in using dynamics, the forces, torques really don’t translate to accelerations because the mass of the screw is small compared to the forces and acceleration. Really, this is more of a statics problem. The forces of friction and the normal force pushing on the screw balance the applied force/torque. Do you remember seeing the video of how I pushed the foundation on my house? Please see this video again and to receive an “A”, please submit a document to me explaining the correction you need for this. Presently a “C”.

Mitchel Hutcheson, Sammie Davis, Grecia Pizano, Nolan Binkele
Title: Examining the conservation of momentum, and changes in energy in collisions.
In the project, we recorded two different collisions of air hockey handles on an air hockey table. The table should replicate a near frictionless environment. We recorded one elastic, and one inelastic collision, measuring velocity in the tracker app, and then estimated kinetic energy transfer and heat energy gained in the collisions.
This video was very well done, you have “B” at present. There is one mistake. It seems you misquote the final velocity… it is close to .35 m/s, or half the max speed of .7 m/s. There is variation (noise) in the measurements. The maximum speed was never 0.85 m/s. The loss of energy can still be calculated, but momentum must be conserved as is, and it seems from your data that it is conserved.

Alec, Weston, Yumi, Vanessa: We will be analyzing a video of one guy jumping up and his friend pushing him horizontally to the left. Here is a link to see what the video is: thought you guys did a good job with this, and I really liked that you had everyone in the video! The dynamics part was (great, but) a little basic. Presently the video receives a “B”. For an “A”, please estimate for the force that the person put on his friend to get him to move horizontally. Send me the calculation. Include a statement as to if this is a force you find reasonable… if you could push this hard.

  OK, this is fine, you have an “A” now.

Edison, Nathan, Jake, Emma: We decided to go more in depth with the spinning chair and changing Inertia example. We will use a spinning chair and weights (backpacks) to show the changes in rotational velocity due to changes in moment of Inertia. We will also analyze the demonstration through an energy lens to calculate the amount of Work done by the person to change the system’s Inertia.  In the energy calculation, it seems you have not squared omega, but your answer would indicate that you actually did square it. 4 kg would be 4 liters… that bottle was not 4 liters. However, arms also have mass, so together it may have estimated a correct change of moment of inertia. As he extended his arms, it is reasonable to say that he did about -20J of work. The video presently has an “A”.

Raul, Trevor Soham: We will demonstrate the conservation of momentum by having one of us throw a heavy bag to another person while both sitting in rolling chairs on a smooth ground. We can use momentum to find the final speed of each chair after the mass is thrown and caught. We can also use dynamics to calculate the coefficient of friction between the ground the the chair. The video is well done. However, it is kind of a trivial example with two equal masses with complete transmission of momentum and energy from one to the other mass. It wasn’t much of a challenge. I do appreciate that you calculated the force. At present, your grade is a “B”. For an “A”, please compare the forces you calculated with something you can estimate with your legs and see if this force more or less matches the force you calculated.

Sebastian Barragan, Frank Brown, Abby Greene, Lena Freid: We will have a pulley system composed of a wheel, string, and different masses. We will calculate the forces acting on the pulley system and the acceleration of the different masses.
Good video!
There are some difficulties with the video:
The torque on the wheel isn’t F_g*R, it’s the Tension*R.
I think it would have been nice to start with the Tracker data so we know in the beginning where the acceleration measurement came from.
The power is increasing not because the kinetic energy is increasing, but because the slope of the kinetic energy graph is increasing. The power is F*v. The force is relatively constant, but the speed increases.
I’m curious how you calculated the centripetal acceleration from Tracker.
You shouldn’t have cut the video off immediately at 5 minutes. It would have been best to shorten the explanations a little to fit the whole thing into 5 minutes. But if you couldn’t do that, you should certainly allow the viewer to watch the entire video.
There is a fundamental problem with your approach in how you calculated friction: You measured the mass of the wheel, not very precisely to be (I assume) 0.2 kg, and assigned it the moment of inertia of a flat disk. However, it is not a flat disk – it has more mass to the outside. Thus the moment of inertia would be greater, no? One must measure the moment of inertia of a wheel… essentially by doing the experiment you did. You could calculate an upper limit on the moment of inertia by assuming there is no friction (dropping this term out of the equation) and finding what the moment of inertia of the wheel would be to conserve energy.
Presently you have a “B” for this very good video. To get an “A”, please either correct the video or send me a document that responds to my concerns.
Correction to Skateboard Wheel
The corrections are good. Your grade is an “A”

Sharon Ng, Brianna Muirhead, Catrina Villalpando: We are doing a block sliding down a ramp problem, using kinematics to find the final velocity, and energy to find the energy lost as heat due to friction. Video link: video is well done. Presently a “B”. Please calculate/estimate the coefficient of friction for an “A”. .   …. after some corrections: This is better! There still seems to be a few problems: the lower left (in red) and the lower right (in red), and your geometry…. Are you correctly labeling theta in all the triangles? I suggest you use a triangle that is far from 45 degrees… like the one in the lower left. Put the mass on the slope and draw gravity and decompose gravity into the perpendicular and parallel components.
– What happens to the normal force as the angle gets steeper? What is your experience on a steep slope? What is the normal force if the surface is vertical?

– Lower right. I think that the normal force and F_g are not parallel, but there might also be a frictional force. Hence, the system being in equilibrium (when the vector sum of the forces = zero) is not dependent on the magnitude of those two forces being equal. 
– OK, now it’s good with your latest document:

Ethan S, Chloe M, Paige L, Jehlia A: For our project, we are going to roll a ball and ring shaped object off a ramp on a table and see how fast each shape rolls on the ramp as well as how far they each land off the table. We will compare the data from each and see how moment of inertia effects the data.
I found this video very well done. There was an enormous amount of information packed into 5 minutes! Additionally, I appreciated the link to the data sheet on Google Docs describing the video. There is one critical flaw: you didn’t separate the velocity into horizontal and vertical components when it leaves the table. If you do this, you’ll notice that the calculation for times in the air will be less (as you measured), and you will not go as far (which you measured). You presently have a “B”, but will have an “A” when you submit to me a document with the correct calculations, and comparison with your measurements. Thanks! Then I received this correction, and all is good. you have an “A”

Sarah, Komal, Ryan, Josh: We will have a person on a sheet and push them on tile for a certain distance. We can time it and have a scale behind the person to know how much force the other exerts to accelerate the person on the sheet. From this data, we can find the coefficient of friction, final velocity, acceleration, and total energy of the system.

Videos for 121 Spring 2018:
Post your plans below this line listing the people in your group and the project you plan to carry out.
Tyven, Ryan, Alex T, Shane
We will be analyzing the mechanics of a bench press. Focusing on the work, power, force, acceleration as Ryan presses the barbell upwards from his chest. OK this is fine: B, but you can upgrade to an “A”. If you look at the displacement graphs, you’ll notice that the speed is almost constant all the way down and all the way up. Hence, Ryan is providing almost exactly F_g to keep the bar moving at a constant speed. The acceleration all happens in a moment when the bar hits his chest,… acting like a spring. Please estimate the acceleration during this moment, and estimate how much extra force is provided by Ryan’s chest if he is still providing a force of 1000 N. If you want to… you could also find the amount his chest caves in and through it estimate the spring constant of Ryan’s chest!:44 What are the forces acting on the Barbell as he holds it at his chest?
Force of gravity: Yes
Normal force: No
Force of Ryan: Yes1:08 How does recording in slow motion affect later calculations?
It doesn’t, no
We will have to convert all the normal vectors to slow motion vectors, no
You will have to convert slow motion time to normal time. Yes1:30 Why do they chose to start measuring from Ryan’s chest?
To avoid having to deal with changing directions, yes
Because it was recorded in slow motion, no
To focus our analysis on a single bench press, YesEmily, Sam, Kodsart, and Rhiana
we will be analyzing the elastic collision between two billiard balls on a pool table. focusing on conservation of momentum and the influence of net external forces acting on the system after the moment of the collision.
This was very well done. However, I don’t understand the large page of calculations. It seems you are trying to predict the final speeds, but you only use one equation? Couldn’t you just calculate the initial and final momenta and add them to see if the total momentum was conserved.. more or less? I assign a “B” and will change it to an “A” if you can explain this to me, or submit to me the calculation. Some details: Negligible usually means very small. The force of gravity are not negligible, they are significant… so, why can we ignore them? And you should have dropped that outlier point, it clearly isn’t correct. You don’t have that speed for the ball… you could just have graphed the data after that point… I just changed it to an “A”. (3:18) What work is being done on the billiard balls?
-the work from Emily’s hands pushing the billiard balls toward each other
-work of friction
-no work is being done.(:54) Why does the position graph show decreased rates of change in position over time after the balls collide?
-the surface was not frictionless
-momentum is not conserved in an elastic collision
-velocity remained constant for the entirety of the recording(2:20) What are other methods of determining final velocities of the two billiard balls?
-changing reference frame
-including conservation of kinetic energy with conservation of momentum
-no other wayAlex, Jackie, Alaina, and Terra
We will be analyzing how rotational kinetic energy changes as work is put in to shrink and grow the moment of inertia of a spinner, thus increasing and decreasing omega of the spinner at Santa Rosa Park.
OK this is fine: A. It is worth noting that the sound quality (or volume) was inadequate. Additionally I think you list the moment of inertia as mr^2. However, Jackie is not a point mass at some radius, nor is she a cylinder. So, you need a coefficient in order to estimate the work she did. You don’t really need this coefficient in order to verify that angular momentum is concerned because her basic shape stays the same – kind of a rectangle, so you only need the ratios of 1.6 that you got.Megan, Rachel, Whitney, Jack
We are going to calculate the momentum of a billiard ball and analyze the transfers of momentum between different balls.
You left something out in this video that is crucial. The first billiard ball did not lose all its kinetic energy or momentum. it’s still moving at the end! However, your video brought up some important issues: friction with the table couples the linear momentum and energy with angular momentum and energy. This is why the ball slows down after you hit it and it is hit: both balls start out with linear momentum, but they are not spinning yet. Also, notice that the first ball stops immediately after it hits the second ball, but it is still spinning, so it begins to speed up again. You might need to slow the video down to see this. Please take a look at the momenta and speeds of the balls immediately before and after the collision and see how close we come to conserving momentum and energy. You don’t have to hand it in. Grade: “A”Genesee Ouyang and Natalia Heller
We will be using a yo-yo to compare the angular acceleration/rotational velocity and linear acceleration/velocity with differing masses. First, we will weigh the yo-yo so we know the initial mass. To begin, the string will be wrapped around the inside/origin of the yo-yo (how you would normally use it), with the loop on the end of the string lined up with the top of a meter stick, and we will let go and watch it descend without adding any additional forces. Then we will tape pencils/other objects if needed onto each face of the yo-yo, weigh it again to get the new mass and do the same thing. We will be asking how different masses affect the rotational velocity/angular acceleration and linear velocity/acceleration of the yo-yo with the least amount of outside forces/torques possible!
I feel ripped off. I never got to see the yo-yo with pencils. What was this about? Was it slower? What’s the conceptual difference? Can you post a video of at least the yo-yo with pencils. Can you please submit a short communication about what difference the pencils made? I assign a “B”. If you can do what I ask, I’ll change it to an “A”. One detail: The moment of inertia has to have a coefficient because not all the mass is at the radius, r. 3:01
If you got a super yo-yo with a radius of 4m and a mass of 1 kg, the moment of inertia would be…?
A) 4
B) 16
C) Very large
D) Incalculable3:08
What would you estimate the value of omega/rotational velocity to be based on these very small moments of inertia?
A) Less than 1
B) Between 1 and 10
C) Greater than 103:18
Do these large omegas make sense?
A) Yes. The yo-yo spins rapidly as it falls. The one without it’s arms sticking out spins slower than the yo-yo by itself.
B) No. Silly students, you increased the mass slightly, so the two systems aren’t comparable.Erika, Pauline, Harmony, Victoria
We will be rolling a exercise ball down a hill at the same time as a tape roller(ring). We will measure the difference in energies(linear/rotational kinetic/potential) between the two, as well as the forces(friction, gravity, etc) that act on each of the objects to see what will get to the finish line first.
This new video is way better, Thanks. However, you did something kind of weird – You found the speed using the video, but you didn’t need to. You could have just used the change in potential energy – AND knowing that v = omega*r. You could have solved the whole thing without the video. Do one thing for me – see how close your answers match v = omega*r… they won’t match perfectly because of road friction, etc.
You have a “B”. Please do this calculation and reflect on the answer and I’ll change it to an “A”Questions:
.02 sec
1. Which do you think will reach the bottom first, the ball or the ring?
A. Ball
B. Ring
C. They arrive at the same time.
.04 sec
2. At this point, which has more linear kinetic energy?
A. The ball
B. The ring
C. The ground
.05 sec
3. Why did the ball win? (choose all that apply)
A. Because it has more linear kinetic energy
B. Because it has less rotational kinetic energy when compared to the ring
C. Because it has less linear kinetic energy
D. Because it has more rotational kinetic energy when compared to the ring.

Annie, Sam, Scott, and Quinton
We will be analyzing the fall of a chicken. We will find the air resistant of the chicken, as well as the acceleration and velocity of the chicken will vary depending on how many times it creates an impulse from its wings.
You start out well, but then make some strange departure that I don’t understand and you have some important mistakes. I would have liked to see the logger pro data, but it’s OK. It seems you correctly estimated the average acceleration to be ~ 5.5 m/s2 and this corresponds to an average force from the wings of about 12 N for the flap of the wings. However, the wings are not always flapping, so when they are, the force must be more than 12 N, and the acceleration must be less than 5.5 m/s2 downward, or even upward when the chicken is flapping. Also, an impulse is F*dt, so the units are momentum(kg m/s) or Ns. So, I disagree with what you’re doing around t = 4 minutes in your video…. You COULD find the total dp from the flapping by finding the difference in the final momentum of the chicken and what it would be without flapping, and dividing that by 3. Each of these impulses would be upward. Watch your units, there are some mistakes with units and what you call acceleration or velocity. I assign this a “C”, by you are welcome to correct it to an “A” if you can submit better calculations to me. While I’d appreciate an improved video, this isn’t necessary.
1) Will the chicken fall faster, slower, or the same speed as a regular falling object? (1 min 44 sec)
2) If the chicken had flapped twice more on its decent, will the velocity have changed? ( 3 min 15 sec)
3) Would a larger chicken with a greater wingspan, but the same mass, be able to create a larger impulse upward in comparison to the chicken we drop? ( 4 min 35 sec)

Alana and Peyton – We will be using an energy lens to look at the loss of energy that a golf ball experiences when it falls to the ground and bounces back up to a lower height, after being dropped from some specified height. We will then drop the same ball from a significantly lower height and analyze the proportions of energy lost, because they should be the same.
OK this is fine: A. This was simple and correct. Well done. What you could have said at the end is that the two values were the same within the accepted uncertainty of the measurements, because you rounded the numbers considerably.
Questions for the class:
1) What lens should we use here? (1min 5s)
2) Why doesnt the ball bounce back to its original height? (1min 58s)
3) About how high will the ball bounce? (4min 10s)

Kayla, Megan, and Toni
We will be using an energy lens to determine the exact height at which we can release a weight attached to a spring so that the weight will tap an egg sitting on the ground without cracking it.
The only thing I don’t understand is how you got the dx and dh, and in particular why they are different. Isn’t the elongation of the spring the same as the change in height? I assign a “B” and will change it to an “A” when I understand. Please explain. OK, explained. That you initially found the spring constant incorrectly. Grade: A
1) Why are we using an energy lens? (0:26)
2) How can we find the spring constant (k)? (0:40)
3) Is there another lens we could have used for these calculations? (3:26)

Amanda, Taylor, Channing, and Katie
We will be observing how the angular momentum of a carousel changes when a moving body collides with it (at rest) at different angles.
This was pretty well done. However, there was an upsetting lack of units at 5:45 in the video, that partially lead to the final units in your answer to be incorrect… at 6:12 in the video. Lastly, please look at the video and see how close to 2m/s your initial velocity is and what the final omega is of the system… Do they match? If not, can you change your guess of what the moment of inertia of the carousel is?
I’ll assign a “C” now. If you make part of the corrections, a “B”, and if you make all of them, an “A”.
What lens can we use to see how impact parameter effects the rotational velocity of the carousel when Amanda runs and jumps onto it? (17s)
Why is angular momentum conserved? (1min 38 sec)

Videos for Fall 2017:
#1 Karina, Gina, Stefan.Throwing a ball How does this affect the horizontal displacement? Time to hit ground?
No video link as of Nov. 20
Nov. 28: The video is not adequate as is in my opinion. There are some mistakes in your statements, and I do not find that you’ve done any quantitative (or I don’t follow it) calculations to give total time or how you calculated speed, etc. Please see me if I can provide any additional guidance. You state, “…turning point is where gravity is no longer in opposition to the vertical component and rather adds to the component in the vertical direction.” You are referring to the vertical component of what? You also state, “… at the end in the vertical direction.” Do you mean, “… in the vertical and horizontal directions?” How were you able to calculate a speed of 8.7 m/s. Is this seem about right to you? How long should this put the ball in the air and how far should it go? Is this what you saw? At 2:05 s, you seem to mix up x and y, but I’m not sure.

#2 Harry, Ben, Matt, JR. We will be analyzing a basketball rolling down an inclined plane, such as a hill. What are the transfers in energy that occurs? What are the different forces that act on the object as they roll down the incline? What are the final/ initial velocities, accelerations, and change in times? What is the coefficient of friction between the ball and the incline?
Well done. There are a few conceptual problems with this. This is a rolling ball, so it is static friction. Thus, friction does no work, and no kinetic energy should be converted to thermal energy. In the first part (dynamics lens), you actually found the minumum coefficient of friction necessary to not slip, not the actual. For the second part, I don’t know what you did. Where did you get the final speed, 2.1 m/s. Did this come from tracker? Note that tracker seems to be tracking a point on the ball especially at the end, and goes in a circle, so the velocity increases and decreases! I think that if you look at your velocity, there should be constant acceleration, no? and it seems there is. However, you should draw a straight line through the data and you will see that the final velocity is less than 2.1 m/s. This is key, because if you put a lower final velocity into your energy equation at the end, you will see that the work done by friction is zero… or close to zero.
2:21 – you mixed up Cos and Sin, but the error somehow doesn’t propagate to the next line.
4:06, – You left out Cos of 5 degrees for the normal force, but it’s so close to 1 that it makes no difference.
5:00, nice that you sped up the video to get through the math.
5:03 – where did the v = 2.1 m/s come from?
5:20 – nice units analysis!


Time 0:41 – So what is the direction of the net force supposed to be?

  1. Perpendicular to the incline
  2. Parallel to the incline
  3. Horizontal
  4. Vertical

Time 1:11 – Total force on y-axis is

  1. g
  2. 0
  3. g*cos 5
  4. g*sin 5

Time 2:53 – What do we know about energy?

  1. KE change into PE
  2. PE change into KE
  3. Heat is also produced in the process
  4. Kinetic energy is conserved

Time 4:52 – From both dynamic and energy lens, mass gets cancelled out, so

  1. Mass is a very important element in this experiment
  2. Mass is just something we can totally ignore
  3. Both lenses are wrong cuz mass is always important
  4. If we have a ball with a greater mass, it’s gonna be hving a higher velocity at the end

#3 Kezia, Jake the Snake, Hailey, Brendan M. We will be bowling using a ramp and bowling balls of different masses. From this we will be calculating the frictional force of the lane, the velocity, and the kinetic linear and rotational energy of each of the balls.
This video link doesn’t work as of Nov. 20.
Nov. 28. Very nice video. However, there are some fundamental problems. Is the moment of inertia of a bowling ball (assume a solid sphere?) – mR2? It would be for a ring, but it isn’t a ring, it’s a solid sphere… so with most of the mass closer to the center of rotation, how would this change your answer? How would this change your coefficient of friction? Also, I think that Tracker has your speed at over 3 m/s, no? It does slow down because of rolling friction, but this happens over a time and you can see it happen. But this is rolling friction. When an object rolls, you can’t really give it a coefficient as if it were sliding. However, you can find an effective coefficient of rolling friction as you did. Please correct your work in a written statement. Also, I think you would be most effective in finding the coefficient of friction by using the dynamics lens and looking at the acceleration as the rate of decrease in velocity on the Tracker graph.
I subsequently received this response from Hailey in this group that is quite good in my opinion.

#4 Kyle, Manny, Shay, Karthik – We will compare the “real” acceleration to our calculated acceleration of an elevator at Baker. We will measure the change in height, time and use a scale to find change in forces.
This was well done in my opinion. Several mistakes are important though.
You gave some numbers to 6 decimal places… really? How accurately have you measured these values?
You have force of gravity, and the normal force? Which one changes and which one stays the same. It seems you’ve mixed up the two forces when you substitute into your equation at ~ 1 minute. How did you get your expected value? Can you discuss this? Is your result consistent with your expected uncertainty (or are your values really accurate to 6 decimal places?).
Lastly, you accelerated longer in slowing down than in speeding up, but the change in velocity must be the same for both (in opposite directions). Thus the acceleration in the beginning must be greater than in the end (which you find). Thus, there should not be a 10 lb difference for both. The change in reading on the scale should be greater in the beginning than in the end. You can actually see this. The equlibrium weight is closer to 131. Then it goes down below 120 and up to 140, so the change is greater in downward acceleration than upward acceleration.
Their answers to these questions are contained in this document.

Time 0:24 – You realize that since you are using F = ma, you are going to be utilizing what lens?
(a) Dynamics
b) Kinematics
c) Momentum
d) Energy

Time 0:33 – What forces are you going to use to solve for acceleration?
a) Tention and the force of gravity
(b) Force of gravity and normal force
c) Force of gravity
d) Tension, normal force, and the force of gravity

Time 0:39 – The acceleration of the elevator near the beginning is _.
a) Positive
(b) Negative
c) Zero
d) Not enough information

Time 0:40 – The acceleration of the elevator near the end is _.
(a) Positive
b) Negative
c) Zero
d) Not enough information

Time 1:58 – How will you find the area under the curve to solve for velocity?
a) Draw a graph and hope for the best
b) Separate the two curves and find their areas using your knowledge of the area of a circle
c) Combine the two curves of the graph and take the area as one whole circle
(d) Separate the graph into sections and use triangles and rectangles to find area under the curve.

#5 Ryan, Jack, Matthew, Khang. We will explain counter steering and how that makes a bike turn.
Not bad! Thanks. The only think I would improve upon is that when Jack demonstrated the concept, he could have made it clear which way he was pushing with his hands.

#6 Ping and David. We will roll different shaped objects down an incline, such as spheres, rings, and blocks. We can measure the speeds of each object using energy and seeing how much work of friction each object does on the surface of the incline. We can see the change in speed and friction as we change the angle of incline.
This was good. However, you should calculate the final speed of the three objects and see how close to correct you were. I hope you measured the distances. Additionally, at 2:50, it’s not that I is greatest because the mass could be different. It’s that I/(MR^2) is greatest.. or the coefficient of I is greatest.
…They did these calculations and it turned out well.

#7 Lauren, Benjamin, Ashley – We are dropping a bouncy ball and calculating the reason behind why it bounces up to a lower height after each bounce.
I’m distracted by the background music. However, you’ll have to ask your colleagues if they think it’s a good idea for them. You mean at the end you lost 0.14 J, not 1.4 J. True? Please make a v-t graph and see if the velocities are what you think they should be. We define elasticity as the portion of the speed that remains in a collision. So a perfectly elastic collision is 1; inelastic is zero. Thus the portion of speed you lose should be proportional to the speed before the collision. You see that a little… in that you lose furst 1.3 m/s and then 1.2 m/s, but there should be a bigger difference in speed reduction. Please check your data and calculate again.
They responded that the’d checked their data and this was correct. There can be other things happening in an experiment that we don’t expect. In “real life” we’d investigate this further, but it is fine for now. Thanks

#8 Connor, Maria, Evan, Ozzie – We are going to roll a marble down an inclined plane with a vertical block at the bottom and analyze it through both an energy and kinematics lens.
This was an ungodly difficult problem to solve, and I commend you for trying. It’s a partially elastic collision at an angle with a book on a table. Some feedback:
– your a-t graph doesn’t make sense because the acceleration changes throughout. In the beginning it’s down the plane. Then there is an abrupt acceleration upwards and maybe backwards, then there is gravitational acceleration downwards. Strange that you don’t have a constant value of 10 m/s^2 during the time the ball is in the air.
I liked the rotational dynamics. Keep in mind that when the book hits, the normal force >> than the force of gravity because the book is accelerating upwards as it hits the ground. The two forces are = and opposite after the book comes to rest, but that’s after the action.
I don’t belive that you should be off by a factor of 10 for your moment of inertia. The surface is flat enough enough and the ball is hard and big enough to be close to “perfect” at these low velocities. Please look through your work and find out what went wrong. Please let me know if you need help.
3:29, they’d go off in the same direction ONLY if they had an inelastic collision, which they don’t. The collision is partially elastic.
I really liked the angular momentum discussion at the end. I would really really like it if you could calculate the angular momentum of the ball before and after the collision and see if the difference = the angular momentum gained by the book… You’ll have to find the mass of the book.
… They recalculated the moment of inertia and got a value that’s closer to what one would expect for a hollow sphere… OK.

#9 Erik, Ahmed, Jason, Oscar – We will be proving that even if things are moving horizontally at fast speeds they still have a vertical acceleration thats the same as an object falling from rest. we will do this by shooting a projectile horizontally from a set height, and dropping a target at rest from the same height to see if they collide.
OK, Some comments
2:15 – Both objects have the same e mass.
acceleration, g, not the same force of gravity. They don’t have the same mass
3:30 – the bullet starts with potential energy AND kinetic energy at the beginning. This all changes to kinetic energy. Does this consideration change anything?
but good

#10 Grant, Amanda, Alexi, David- We will use a carousel and analyze the changes in linear and angular momentum. We will also consider momentum of a point mass and how momentum changes if the carousel is spinning initially or at rest.
This was great… There is just one thing you say that is kind of awkward for me. at 40s, 100% of your momentum is always linear. I think you mean to say that he has no angular momentum when he is headed right toward the center with an impact parameter of zero.
Good job.

Time: 0:14
Will the wheel have a change in angular velocity?
a. Yes, its angular velocity will increase
b. No, the carousel will stay stationary
c. I think Grant will fall off the carousel and die
Time: 0:46
Will the carousel have a change in angular velocity?
a. Yes, its angular velocity will increase
b. No, the carousel will stay stationary
c. Grant will almost assuredly die this time
Time: 0:55
Where did the angular momentum of the wheel come from?
a. Some of the linear momentum was converted to angular momentum
b. Grant had an impact parameter which gave him initial angular momentum
c. Grant did not have initial angular momentum so I have no idea why it started spinning
Time: 1:09
Where did Grant’s linear momentum go?
a. It was transferred to the angular momentum of the carousel
b. It was not conserved because the carousel was not moving linearly after the collision
c. It was transferred to the earth

#11 Benji, Kirsten, Delaney- We will be using the energy lens and the dynamics lens to determine the height necessary for a cart to have the same acceleration on an incline plane and a horizontal pulley system.
OK. This seemed to be the same problem we did in class and for a problem set, no? Still, it was very well executed. Good job.

Videos for Spring 2017:
#1 Taylor Morris, Emily Garcia, Lauren Seibert. We will be calculating the power behind throwing a basketball by finding the kinetic energy of the ball as soon as it leaves the thrower’s hands, then calculate the work, and from there, the power. How did you find the mass of your basket ball? The number you used is about the same as a gallon of water. I think the mass of a basket ball is supposed to be 0.625 kg. Please pick up a basket ball and move it around. Please pick up a gallon of water and move it around. Does your power calculation seem reasonable for the amount of effort you put into throwing the basket ball.
After realizing that the ball should be inflated to 8 psi, and that the mass of the ball was .625 kg and not 8 lbs, our new KE = 1/2(0.625kg)(7.84m/s)^2 = 19.208 J. This makes our actual power = 19.208J /.267s = 71.94 W.
OK – good

#2 Bradley Livingston, Eric Schwegman, Clara Briley, Hunter Wood, William McTaggart. For our project we will be looking at the incline planes of two hand railings on campus. One is steep and Eric accelerates down it, while the other is less steep and Eric sits at rest on it. We will be calculating the accelerations down the inclines, the force of friction, the work friction does in the system and then the final speed. We will be comparing the calculated accelerations from the dynamic lens to the acceleration we obtain through kinematics in the video to see if we were close.
One IMPORTANT mistake here: you state that the force of friction in the first scenario – mu*normal force. Mu*normal force is the maximum amount of static friction that the surface can provide. The angle of the incline should not determine the coefficient of friction, right? There’s a problem with your calculations. Acceleration should depend on coefficient of friction, so there’s no way you can calculate both of them without measuring one or the other. You have calculated a final speed of 4 m/s. However, from your video, I see the slide lasts about 2 seconds indicting a speed of about 1 m/s and a final speed of about 2 m/s and an acceleration of about 1 m/s^2 indicating a coefficient of friction that is about 0.1… I think, please check. The reason that you got such a low coefficient of friction is that you made a false equivalent: Your first equation in the upper left is an energy balance: the change in potential energy is equal to the work done by gravity… period. You added the work done by friction, which is not correct. Because the change in potential energy IS equal to the work done by gravity, you should have calculated a coefficient of friction of zero, but your numbers were not perfectly precise, so you just got a very low coefficient of friction. Please check this out. What I suggest is that you work backwards… correctly measure the acceleration and calculate the coefficient of friction. Then you could measure this coefficient by pulling on your colleague sitting on horizontal railing and measuring the force necessary to make him move. Besides this disastrous mistake, I found this video very well done and the equations nicely visible and well explained! Thanks.
You are right, the coefficient of friction should be a constant since the same two materials are in contact in both cases (the railing and Eric’s shorts). We know force normal and the force of friction change with the incline plane’s angle — the greater theta is the lower these two forces are, but the coefficient of friction remains constant. Realizing this, we can see that this coefficient of friction is easy to calculate from the example in which Eric is in equilibrium. From our measurements, we find the coefficient of friction to be 0.1. Because we now know our coefficient of friction, we do not need to use the energy lens (which lead us to the false equivalent you mentioned). We calculate the new acceleration to be 2.53 m/s^2. Additionally, our new coefficient of friction means that the force of friction is different from what we initially calculated. We determined the new force of friction for when Eric slides down the railing to be 56 N (not 28 N) and the work of friction to be 123.2 J (not 61.6 J). As Eric slides down the railing, his potential energy is converted to kinetic energy and heat. We calculate the final velocity to be 3.8 m/s. We would need to look at the video closer to get more exact measurements, but as of right now our velocity and acceleration from the video (calculated through kinematics) remains the same. Future projects on this topic could choose longer railings so they can have a longer video and displacement to work with when calculating their values through kinematics. Hopefully, that would make it easier on them and they would get more exact measurements to compare their calculations to.
It seems you didn’t address several of the points I brought up. You can leave it as it is, but you will get a slightly lower grade.

#3 McKenna Troje, Jake Everest, Bella, Cameron. For our project we will be taking a ball attached to a string and calculating the tension on the string as we spin it in a circle above our heads at different radii.
You state a few things that are incorrect. One is that the tension = ma. Tension is only one of the two forces on the spinning object. You stated correctly that the vertical component of tension = mg (please add because we’re in equilibrium in the y direction), so it’s just the horizontal component of tension that = ma. Did you distinguish the radius of the circle from the length of the string? The radius is only the horizontal component of the length of the string. McKenna states that of course omega increases when you make the length of the string shorter… but you are in control of omega. Were you trying to spin it at a higher omega? Was anything conserved? Were you keeping the speed the same? Maybe you were, but it is not necessary that omega increases as the string is shorter. I think it would have been very nice if you included two things: measure the angle of the string using the video to see if the angle is consistent with the acceleration and g. And you should see how close to the measured tension your calculation is. I have tension meters you can use. Nice description
What we really wanted to show here was,was that as the radius gets shorter it’s easier to swing the ball in a circle. This is what you experience in real life, imagine it’s very easy to swing a ball on a string that’s half a meter long, than if the ball was on a string that was 5 meters long-that would be really hard! It would have been good to mention in the video that we were trying to swing the ball in a circle with roughly the same amount of effort(power) each time. So instead of looking at the tension of the string, it may have been better to look at the angle, theta, that the string makes at my hand. The easier it is for me to swing the ball up into a circle, the closer the ball will get to being perfectly horizontal, which means theta will approach 90 degrees. By pausing the video, I was able to draw the tension vector, gravity, and observed accleration vector of the tennis ball. Since we know the string, or the hypotenuse, is 1 meter you could then use that to estimate the magnatude of the other vectors. From there using trigonometry I found the angle by our hand when the string was 1 meter to be about 73 degrees. Using this same method for when we shortened the string to 0.5 meters we found the angle to be about 79 degrees.

I don’t understand what it means that it is harder to make a ball spin over your head with a longer string. Does it mean it has to have more kinetic energy for the same angle, or that you have to provide more force for the same angle? How would the FBD support your statement. Please provide me with some quantitative answer to this question.

The tension in the rope is a ratio of the velocity^2 over the radius of the rope. So if we were to imagine the rope was infinitely long, we would have to have an infinite velocity in that rope to maintain that ratio, a feat that would be impossible for us. However, if the radius were incredibly small, the velocity can be also very small, which is why it is much easier to maintain the same tension at a lower radius.

#4: David, Matt, Jeremy, and Josiah decide to go biking. They sit on their bikes at rest at the top of a hill, ready to ride down. Their goal is to find the amount of thermal energy lost at the bottom of the hill. They expect their potential energy to convert into linear kinetic energy and rotational kinetic energy of the wheels. This would be explained through an energy lens of course, since there is a conversion involved. In this system, they could also figure out how much of the energy is lost to heat and friction by comparing the theoretical speed to the actual based on the initial potential energy. They will be figuring out the height of the hill using an altimeter and taking the difference between the top and bottom of the hill.
I like how you said, “the change in height is about 4 meters”… but I don’t like how you carried your calculation out to 6 significant figures. We have no idea of the value of the last 4 of them. Altimeter? What’s this about? Do you have the ability to measure elevation to a millimeter with your cell phone!” Wow, then likely I do too. There’s something very important here that is messing your your data collection: Parallax – Tracker is only able to see the motion perpendicular to the direction to you! Notice the velocity – time graph. It indicates that the speed rapidly increases at the very end, when this obviously isn’t true from our experience, and you can visually see that the road kind of flattens out near the end. What’s happening is with a kinematic lens, Tracker measures speed by change of displacement over time increment. But it can only see movement that is perpendicular to the direction to the camera. The bicyclist is largely traveling toward the camera, so the change in displacement isn’t evident. Then near the end, as the rider comes by the camera, the perpendicular component of the velocity becomes significant. If you correct for this, you will likely find that the final speed is pretty close to the theoretical value. Additionally, you did not take into account the extra energy needed to get the wheels spinning. In order to do this, you could measure the mass of the wheels and include the rotational kinetic energy, which would slightly reduce the theoretical final energy. One way to make this simpler, is to estimate that a wheel has all the mass on the rim (not a bad estimate), and recognize that the speed of the wheel rim about the hub = the speed of the bike on the ground (= omega*R). Thus, bicyclist racers know that as far as acceleration is concerned, the mass of the rims counts double: because you have to accelerate this mass forward and you have accelerate it around.

Our Revised Work.

#5: Megan Miyake, Jeyca Domingo, Austin Keller, and Mabel Shah. For our project, we will be analyzing the energy transitions of a soccer ball after being kicked, as well as the work and power exerted by the kicker. We can also calculate kinematic properties such as displacement, velocity, and acceleration. Questions: 1) 1:00 Will the mechanical energy be the same before and after the ball is kicked? 2) 1:20 If we were to calculate the energy transition from the peak of the ball’s path to it being caught, how would that energy transition look? 3) 2:34 Without calculating the final velocity, what do you expect it to be close to, knowing that momentum is conserved and from watching the video? 4) 3:17 How can you find the velocity of the ball? Find it.
Good use of Tracker for clear graphics. Your energy conversion isn’t correct. Heat from your body isn’t converted into work on the ball. I think it would be better to state that in the kicking, your internal chemical potential energy => kinetic energy of your leg, that has partial elastic collision with the ball. The only energy that is easy to measure is the resulting kinetic energy of the ball. The power of your leg is actually rather substantial because the ball gets all its kinetic energy from your foot in a moment: you can use the video to see how long your foot is in contact with the ball. However you may find it more instrumental to measure the rate of power transfer to your leg – how much kinetic energy did your leg have, and how long did it take you to put that kinetic energy into your leg? It would be an interesting exercise in estimating the kinetic energy of your leg… kind of hard, because our leg isn’t a simple geometric object. I think at the base of your logic is that the kinetic energy of the ball turns to potential energy and heat energy. Do you think that there was significant friction involved with the ball after it left your foot? I think you forgot that there is still kinetic energy when the ball is at the top of the arc – in the horizontal component of the velocity, which remains unaffected by the force of gravity because the force of gravity is downward. Please calculate the kinetic energy of the ball at the top of the (parabolic) arc from the horizontal velocity and add it to the kinetic energy the ball gains, and my guess is that it will be very close to the initial kinetic energy of the ball, as well as the final kinetic energy of the ball. In your initial momentum equation, it states that the initial momentum and final momentum = zero. However, initially you are not moving and the ball is moving, so there is a total nonzero momentum beforehand. Also, it’s not really true that there are no outside forces on the system, as you are standing on the ground. It would be different if you were standing in a boat that was able to recoil after you caught the ball. The mass of your body doesn’t “cancel out” of the momentum equation… it’s just equal to zero before the impact because you’re not moving. By using the conservation of energy to find the speed of the ball, you are only finding the vertical component of the velocity… which would push you downward when you catch the ball. The horizontal component of the velocity is constant through the flight, and you can find it from the videos with a kinematics lens… or Tracker. You can see from the final angle the ball makes with the vertical that the ball’s horizontal velocity is a little less than the vertical velocity. You might reflect on your final velocity of the ball/girl system: 0.07 m/s… a little less than 1/10 m/s. This is pretty slow . Could you see it in the video? If you slow the video down, you can see that she steps into the ball, so she has momentum in the opposite direction. likely she slows by about .05 m/s. It’s not clear if you could recognize it.

We decided to redo our entire project due to the complexity of the original project. In our new one, we looked at the energy transitions of a volleyball being thrown straight up, and the power being exerted onto the ball. To find the power, like suggested we used the change in kinetic energy over the change in time and again used tracker for graphics, the time and velocities.

The physics here is much better. There is one problem I have. The power she provides is the increase in energy per the amount of time that she is giving that energy. Is she pushing on the ball for 0.9 seconds? If her arms are about 1 m long and the speed when she releases it is about 5 m/s, what’s the average speed of the ball, and what would be the time it takes to do this? Also, can you measure the amount of time that she is pushing on the ball from Tracker?

#6: Michelle Huang, Frederick Kim, Megan Logan. For our project, we will be looking at elastic collisions with pool balls through the momentum lens. We will be hitting a pool ball at rest with another pool ball, and calculating the final velocities of the two balls. We will be using Tracker to find the initial velocity and angles at which the balls go off at, and then we will be using x and y components to solve our calculations.
This was lovely, simple, and correct…. but please please, finish it… Please show the final momentum vectors adding to the initial momentum vector. Also, please verify how close your answers are by using Tracker to measure the final speeds of both of the balls. You will likely find that the system is not completely without outside forces – there is some frictional force, so how should the measured speeds compare with the theoretical calculated final speeds?
I see you’ve sent me a document. This was sufficient.

#7 Aaron Lay, David Chau We will be analyzing the reasons why gravity slingshots/gravity assists are used in space travel, how they work, and analyze the mechanics of how they work. We’ll analyze the angular momentum, angular acceleration,and other relevant forces that relate to gravity slingshots.,
You guys! this is hilarious! It was also very well done in my opinion. You consistently use L for momentum. Please correctly distinguish angular momentum from momentum. You also took a significant amount of this video from another video. When you do this, you need to acknowledge the source in order to not be vulnerable to accusations of plagiarism. I can’t stress enough that you should be very very careful of this in academic circles… you could lose your job for it. I’m a little double minded about how to accept this. You didn’t do anything. Don’t you think you should do a fly by of some massive supergiant and make a video of it?… or find a way to simulate this on earth? Please talk to me about how we could do this. You could hit a ball in an elastic collision for instance.

#8 Cruz Calderhead, Ryan Boehm For our project, we will be analyzing the motion of a spinning basketball on a finger. We will be analyzing how much angular momentum it takes to keep the ball on top of a finger without falling. We will be watching and recording the necessary force that needs to be applied to the ball the give it enough angular momentum to keep it spinning.
Video #1:
I’m concerned about your initial vector diagram. You need to straighten out the physics and do this video again. Why are the sum of the forces zero in the y direction – did you mention if the system was in equilibrium? Did you identify which lens you’re using? It seems you have made a vector addition diagram and labeled one of the forces as “m”. Is mass a force? I think that the other force is F_G… force of gravity? This diagram is repeated several times throughout the video. You say the the force of gravity is less than the angular momentum of the ball. One is a force (in Newtons), one is angular momentum (in J*s or kg*m2/s). The universal gravitational constant that you wrote on the video is not gravitational acceleration – do you understand how this constant is related to gravitational acceleration? You state that the forces on the ball don’t equal zero, so it has velocity… I think you mean then it must be accelerating. Additionally, When the person catches the ball on their finger, I think that the ball is already moving downward and slows down, so the acceleration must be upward (kinematics lens). The momentum of the ball wouldn’t “come to a stop.” I think you mean that the angular momentum of the ball is now zero. You talk about gravitational velocity? what is that? And how would “gravitational velocity” be “less than angular momentum”? Thanks for putting the URL in so I could find the video of the person explaining how to do it. I would like you to correct your statements of this video and maybe explain why spinning the ball makes a difference. Please consider which words you use and the connection they have with the material we covered in our class.

Video #2:
This updated video is much improved. You got all the dynamics correct and most of the angular momentum… a few details. The force of gravity is 6.2 N not 62 N. The ball was never in equilibrium in the air. After it left his hand, it was immediately accelerating downward at 9.81 m/s2. You should take out the universal gravitational constant: 6.63…. because it has no relevance to the problem unless you want to consider the mass of the earth… but that’s not where you’re coming from here. For energy you got a good start, but didn’t finish: The potential energy converted to kinetic energy, and did some work on his finger as his finger depressed. For the torque due to gravity, you say that the perpendicular component… perpendicular component of what?… Torque = F x perpendicular component of the radius. Lastly, you don’t show the addition of angular momenta quite correctly. You have to add the vectors nose to tail: Initial angular momentum plus the change in angular momentum (dL = Torque * dt) equals the final angular momentum. But really, this was quite well done. You can either revise your video and post it a third time, or hand in a paper with the corrections.
Basketball Spinning Correction Document

#9 Eduardo Gutierrez, Yusuf Bahadur, Prith Jaganathan, Alex Valdivia. For our project, we will be giving an in-depth analysis into different types of collisions. And by using a momentum lens, we will be able to get the velocity and masses for our different experiments. The experiments will vary anymore from impact on a pool ball from a billiard stick to a crash between two cars.
Everything seems correct to me. Is this an elastic collision? How much heat was produced?

#10 Garrett Landress, Emma Salam, Andrew Jarboe, Emily Bohannan, Eva Taupier. For our project we are making 2 videos (because we have 5 people) analyzing a bungee jump from an energy lens. We will analyze the GPE to KE and the Spring Constant of the bungee.

You should put the URL in for the video you used for two reasons: (1) I want to find it. (2) you don’t want to be accused of plagarism… you don’t want people to think you are claiming to have made the video yourself. Pretty good… you wrote N/m for the spring constant, but you said, “Newton meters”. Which is correct? How does a spring work? When you say, “that’s it” I’m thinking, “no, please more!” Does the video continue to show the person hanging motionless? If so, then you can find the equilibrium length of the spring with the person hanging on it. This will give you another spring constant. Is this spring constant the same as the previous one you measured?

The second video link, which I assume is the updated and improved video link, is unaccessible. Youtube says it isn’t there at all.
We fixed the second link, it is another version of the video done by other members of our group using a different mass:

The original bungee video is a promo for a bungee jump company in New Zealand. This is a link to that video:
Unfortunately the video does not show the jumper hanging motionless. Therefore we cannot calculate equilibrium length as you mentioned in the comment. 🙁

#11 Jack Brereton, Brenden Schow, Robert Harbicht. For ourproject we will be making a 1 video explaining the benefit of getting into a hammock upside down and then spinning over. We will calculate the centripetal acceleration needed to flip over 180 degrees (sitting upright). 1. (0:50) Would the system be affected differently if the hammock was lower? If so, how? 2. (2:25) Calculate the centripetal acceleration if the rotation was 360 degrees. 3. (3:30) How do the strings of the hammock affect the forces through tension?
This was a fun video – good introduction and good graphics. I think what you measured isn’t exactly the same thing you thought you measured. He wasn’t spinning around an axis at a radius of 75 cm. Rather, I think he rocked back and forth a displacement of about 75 cm. 3.4 m/s is about 8 mph. Do you think your velocity was that high? You left off something very important… what about gravitational force. This is a dynamics problem and really needs a free body diagram. I think you need to identify the circular motion (did he really rotate in a circle of radius 75 cm?), where in this circle was he when you checked the force? Where was gravity? I think that the video you needed to make was someone pushing him hard enough to execute the circular path… but that might be hard.

I’ve received nothing from you as an update.

#12 Jack Maughan, Nick Williams, Eugene Long we made a video of Jack applying a torque on a object so we will either calculate the amount of NRG jack needed to turn the wrench, or the force that was generated by the wrench.
Oh, I found this so professional… this will go viral in the mechanics circles… don’t you think you should reference the video where you got this idea so people will like me too? You say that the force you apply at the handle gives a much larger force at the threaded rod… but really you should say “torque”. Ok,… good enough. Sound quality was awful – why weren’t all those people sitting and listening? You really should have divided by the length of the sleeve, providing the force you got (because force is the gradient of the energy). Additionally, you don’t want to divide by the radius of the nut, but rather the radius of the threaded rod… yielding a larger force than you got. Lastly, most of the work you put in went into heat, because the frictional force you were working against was more than the horizontal component of the normal force on the threaded rod (which goes into moving the device upwards). We know this because when we let go of the wrench, the frictional force prevents the nut from moving backwards. The easiest way to do the energy calculation would be just F*dx, where F is his 220 N, and dx is the distance he went around in a circle however many times it took to raise up the cylinder. But it is fine what you did too.

#13 Jason Kehl, Brian Keene, Jessica McRoskey, Ryan Schioldager. We will use dynamics to analyze why a curveball curves as it approaches the plate. We will explain why professionals are so much better than the average Joe and how to optimize the “curve” in a curveball.
OK… I think you could have done this simply with a momentum lens. If the air gains upward momentum, then the ball must gain downward momentum in order to conserve momentum. Note that the reason you don’t put the upward force on the air in the FBD is because it’s not a force on the ball… you didn’t say that. I myself would have put that note and force somewhere far away from the ball so it didn’t get confused. I think you should have thrown some balls and taken a video of the ball “breaking”. But you mention that a ball will “break” 17 inches… about 50 cm? in a pitch… a full second? – never! I’ve seen a baseball game, there’s no way that’s a full second. At ~ 60 ft (20 meters), at a speed of 100 mph (~ 45 m/s), we get a little less than half a second. What would gravity do in half a second? it would get up to 5 m/s… average speed of 2.5 m/s for half a second, we have about 1.2 meters… so gravity alone would bring the ball down from a horizontal path more than a meter. I guess the “break” from a curve ball is an additional half a meter?

Our Group first analyzed the system using a momentum lens. We have attached a diagram to describe the relationship of the momentous. We also described why we put the force of the air on the FBD even when it was not acting on the ball. Lastly the 17 in. statement was referencing an additional movement in addition to the force of gravity.

#14 Jenna Van Mouwerik, Sabrina Hetzler, Ginny Geddie, Darlene Ifeorah. For our project we will be winding ourselves up in a swing and then spinning. We will be measuring the change in the moment of inertia and omega as you change the radius by sticking your legs out or pulling them back in. Questions: 1) At 1:41: Calculate Jenna’s moment of inertia with her legs out: a) 24.3 b) 27 c) 7.5 d) 15, 2) At 3:55: Why does Jenna spin slower with her legs out? a) she has a greater radius, and therefore a greater moment of inertia b) she’s slowed down by the friction of the wind c) she has a greater radius, and therefore a smaller moment of inertia, 3) At 5:15: Why does she speed up after the first two rotations? a) Because her inertia has decreased b) Because her inertia has increased c) Because she has gained rotational kinetic energy d) Because she has lost more potential energy, 4) At 6:04: Predict the relationship between inertia and omega: a) as inertia increases omega increases b) as inertia increases omega decreases c) as inertia increases omega remains the same
Thanks for an interesting video here. A few oversights… You fall into a common trap here. When you pull your body closer to the center of rotation, it’s angular momentum that’s conserved rather than kinetic energy…. this is because you are doing work pulling the body in providing the centripetal acceleration with the force. You certainly overestimated the change in moment of inertia because Jenna’s body is much more than just legs. Her torso doesn’t really change position so much, so her moment of inertia probably changes by much less than the factor of ~4. You could actually compare the changes in omega as she pulls her legs in and out to measure the ratio of the moments of inertia. Please do this. Also, the kinetic energy conservation is good to look at how the swing increases in speed as she unwinds. This is actually a gravitational potential energy, because he body drops a little as she unwinds… right?
We decided to write/ draw out a correction and response:
Part 1:
Part 2:

OK, Thanks

#15 Joshua Grassel, Stuart Ross, Jorge Rios, Brian Phan. We will be investigating the dynamics of Stu sliding to a stop on his skateboard as well as the energy transitions involved.
This was slick (in my opinion). Nice demonstration and video. Nice, clear presentation at the board, and thanks for speeding things up when you were substituting values in (please, not “plugging”). Please state why the force of gravity and the normal force are equal and opposite. I really like how you had the frictional force in Newtons, but then went back to m*a when you calculated the coefficient of friction because the masses canceled. It illuminated that mass doesn’t matter, but also made the problem easier… (hurray). I thought I’d learn skateboarding when my son was learning it at age 6… down at Santa Rosa skate park. The kids loved it, they were all over me…”Hey, Pete, here’s how you do an Ollie”… if the board shoots out, you yell “board!” They were giving me all kinds of lessons. I promptly fell and broke my wrist and was yelled at by a mom for not having wrist guards and being a bad example for her kids… I thought breaking my wrist because I had no guards was being a good example for the kids… kind of like a public service.

You didn’t answer my question and state why N = mg, but it’s OK. I think you know that the acceleration in the vertical direction is zero = vector sum of the vertical components of force.

#16 Colin Patterson, Cameron Storton, Sam Kuennen, Aaron Wright, Daniel Yeh. We will be investigating the force and energy we put into a pedal stroke on a bicycle and how that will affect the velocity and angular velocity of the bike and wheels based on what gears we are in.
very nicely done. What was your software package? You say “horizontal component of gravity”… I think you mean “x-component of gravity”, right? I think you over state your precision with your 4 significant figures of force…. maybe 102 N, or ~100 N would have more correctly represented your precision. Wait just a second! Power data? Where did that come from. You’re holding out on me. You have some interesting bicycle diagnostic. Please explain. You might put your power in context… was that has hard as you could pedal? how long could you pedal that hard? How many horsepower is that? Does it seem reasonable? You could also calculate the torque on the pedals and or the torque on the rear wheel. But I found this nicely done. Please explain where the power data came from.

I would like you to please respond to my questions.

#17 Leslie McNeal, Kellen Haug, Tiffany Vu and Blademir Osorio. We will be analyzing the increase in velocity of a coin rolling on it’s side in a conical well as it gets closer to the center of the well.
You state that as the coin drops, it’s acceleration will increase inversely with the shrinking radius… what does that presume about velocity? Is this presumption correct? What is conserved as the coin drops? what is not conserved? Is centripetal acceleration = omega^2/radius? What units would this give us? Remember omega is in units of 1/s. Alpha is a symbol used for angular acceleration. Are you finding angular acceleration or linear acceleration… which is centripetal acceleration? What should the units be? What are the correct units of your first calculation of alpha? It seems you’re assuming that omega remains constant. Please look at the video and see if omega does remain constant. The presentation was clear with clear graphics and clear audio. Please get the physics straightened out and do it again. I think you need to invoke Tracker or some other means to determin the speed at different times. Please talk to me if you need help.
Redo video:

I like how you used Tracker. However, something is very wrong. How can the radius be 1.6 m? that’s almost as tall as you? How did you get these values. Maybe you can talk to me about this Tuesday 1-5 or after the exam.

The calculations centripetal acceleration of our second project are as follows:

At radius 0.845 m (diameter of 1.69 m)

centripetal acceleration= 0.475 s^-2

At radius 0.588 m (diameter of 1.176 m)

centripetal acceleration= 0.847 s^-2

At radius 0.072 m (diameter of 0.144 m)

centripetal acceleration= 2.592 s^-2

At radius 0.0465 m (diameter of 0.093 m)

centripetal acceleration= 2.616 s^-2

#18 Monique Rea, Tyler Burnham, Nina Succar, Anthony Griffin
Here’s our project done on Vector Components, for this project we analyed a box being dragged on a near friction less surface by a string. For this project we would increase the angle at which we dragged the box to see how the increased angle would affect the speed of the box if we pulled the box with a constant tension force. In this video, you will see what forces act on the box as we pull and how to solve for the speed using dynamics and energy.
Analysis seems correct, but bears little similarity with the demonstration. Additionally, there is no consideration of friction, and the system you use is largely friction (rather than mass/inertia) dominated. Please find a 25 kg mass and a string and pull with a known force. You could find a light cart and some masses, and I can provide a force measuring for you to pull with, if you want to.

I appreciate that you came in and did this experiment again. I look forward to seeing the result.

Below this line is from Fall, 2016
By Tuesday of week 9, Nov. 15, students will post proposed video projects. You have until Thursday of week 10 to post the actual video project.


#1. Harrison DeWitt, Will Eggart, Erik Henrikson, Mike Klee. We will be riding an electric scooter up a hill, analyzing the linear and rotational kinematics of the wheels, as well as the energy transformation. We will use this information to find the power done by the motor.
I like what you did with tracker and the calculations you made. However, I can’t read anything you have on the board. Also, the camera moves periodically. I think you should spend more time on the graphs. Please allow the velocity curve to be a curve, and you’ll notice that the acceleration decreases over time… this should make sense. The electric motor loses torque as the speed increases (you may learn about this in PHYS133)… and frictional forces increase. I find this interesting. If you multiply the acceleration by the mass, you’ll have the force of the motor. If you multiply the force curve by the velocity curve, you’ll have the power as a function of time. I think this would be very interesting. You see that you can only multiply the curves because the data points themselves have way too much noise. I think you should take another video of your explanation because I can’t see anything in it. I can give you better markers.

#2: Allie, Shane, Riley. We are going to investigate the mechanics involved in hang gliding by examining the glider using a dynamics lens, specifically how different glide angles relate to the forces exerted on the glider. Hang gliders are affected by the force of gravity as well as a normal force from the air keeping it above the ground. These forces are dynamic and change when the glide angle and wing angles change. Our materials include a hang glider, a camera, and hill to launch off of. We will calculate the glide angle and observe the movement to calculate how gravity and an aerodynamic force are interacting to move the glider in different ways.
I like the video. The quality was great. Notice that not only where the values for the spring constant slightly different, but Shane’s were always larger. this is because the slack line (unlike a spring) is not linear with length. The further you stretch it, the larger the spring constant is. Could you please calculate the tension in the slack line for one of the scenarios? You won’t be able to match them because the tension is different for initial tension (T1, T2, T3) and for each person. Note as you step onto the slackline, the horizontal tensions also increase.

#3: Avery, Josh, Pri. For our project we will be trying to better understand this idea of precession by analyzing the motion of a spinning top. We will be delving into our “experiment” by carefully watching and recording whats happens to the angular momentum and direction of a spinning top when we apply a force to different parts of it while it is spinning. We will also look at the direction of its angular velocity and calculate the angular momentum for each case.
The video was nicely done. However, you don’t explain precession correctly or label the different quantities such as omega correctly. We should talk about this.

#4: Ali, John, Alec: We are undecided between evaluating an ice skating move from the movie Ice Princess (Disney 2005), and evaluating the interaction of forces needed in order to right (bring upright) a capsized sunfish (small boat).

Your group took on a very challenging analysis and I really like the way you mixed in many different concepts and also interplayed the discussion with the videos of the skater. I have a couple of concerns and I would like you to focus on one part of the analysis to please get it right. For the video itself, I would like the volume to be louder, and there should be no black screens. Please fill the screen time with images. There are three physics things you didn’t get correct:
1) you can’t equate angular momentum to momentum. These are completely independent and different animals. They have different units. The Veritassium videos we saw with shooting the bullet into the block demonstrated that we conserve momentum and angular momentum independently.
2) In order for an impact parameter to make sense, I think you need to have an impact. The impact parameter is the perpendicular distance between the center of mass of the system and the projectile’s velocity. As it is you find that the woman is leaning over and starts a turn. This isn’t an angular momentum problem, but requires a dynamics lens. It’s kind of like a conical pendulum, like the bicyclist leaning into the turn. You could do this anaylsis instead.
3) You use an energy lens to see how high she goes in her jump. However, this is not correct because her linear velocity didn’t turn into vertical velocity which would have allowed you to equate her initial kinetic energy to gravitational potential energy. Instead, she jumped upward so her gravitational potential energy came from work that her legs did while she was moving forward.

#5 George, Alex, Amanda, and Tim: For our project we will be looking at how water on a trampoline can affect the tension of the net and the jump height of the person. We will do two runs, one with water and one without. Using dynamics, we will investigate the tension in the net of the trampoline by observing at what angle the net bends downwards. Water may have an affect on the tension which could affect the jump height of the person. [ ADDENDUM: ]
This was well done. It assumes that the spring constant for a trampoline is actually constant. This probably isn’t the case, but may be a reasonable approximation. You have calculated that his acceleration should be about the same as gravity (only upward), but you could also have measured the acceleration using tracker. Can you do that for a calculation please?

#6 Patrick, Derek, Chris, Alicia: For our project we will be looking at the torque applied to a lug nut and how it must overcome the static friction to loosen the nut. We will also look at the kinetic friction as the nut gets tighten to become static. CHANGED to finding static friction coefficient in terms of centripetal acceleration.
I think the video is pretty good. Points of improvement: In your FBD, please ask the question and state the answer. Also please make the forces originate from where they are being applied: gravity from the CM, but the friction and normal forces are applied at the wheel/pavement interface. Also, please note that the coefficient of friction you found is the minimal possible unless the car slipped on the pavement.

#7. Steven, Brandon For our project, we will calculate the change in energy as we swing on a swing set. We will compare the gravitational potential at the beginning of the swing to the rotational kinetic energy as we are swinging.
I liked your video. There are two mistakes that I would like you to correct. You calculate his potential energy with respect to the ground, but he doesn’t swing with his CM down to the ground. In order to find the kinetic energy he has at the bottom of the swing, you need to use the change of elevation of his CM. The second mistake is that it seems (although I’m not sure) that you took his speed and said it was the same as his angular velocity, using the (incorrect) units of m/s for angular velocity. Please explain this better and if there is a mistake, please show how to make it work correctly. I like that you used the accelerometer in his cell phone. You should show how this works and provide all the data. That would be super cool for me because I don’t know how to use one.

#8) Dhairav, Lawrence, Cody We will study precession of a bicycle wheel and find its angular velocity of precession and the time period of the precession. We will use angular momentum to explain the phenomena and how different variables affect the angular velocity of precession. We will include a clipping to support the calculation and prove that time period of precession that we calculated is the time for our bicycle wheel to precess around the string once. Questions: 1) 0.32 What is the angular momentum? is it correctly shown in the video? If not, what should i have said? Ans: Angular momentum caused by the torque due to gravity. 2) 1.19: Is tension really equal to gravity? Think about directions and magnitudes. 3) 1.23: I meant net some of torques is not equal to 0. There is a torque acting that imparts a change in momentum on the wheel. 4) 4.16: or the number of times the wheel spins around the string in one second. 5) 5.18: i used the left hand. Is that right? 6) 5.58: this can also be looked at from a momentum lens where final l = initial l + impulse. Where torque=time*change in momentum. 7) 6.34: i meant angular momentum is higher.
Good video. You label omega where you really mean tangential speed. You don’t carry your units through the calculation (I’m aghast). I think you should start with the video of the precession so the viewer knows what you’re talking about. Then you can give the explanation of why this is happening. and lastly you can do the calculation and match the numbers to see if your calculation was correct. You should state that the drawing for the angular momentum is as viewed from above. Be careful between using “angular momentum” and the change of angular momentum from the torque of gravity. You made one mistake I saw. You said that if you spin faster, the angular momentum was lower. I think this was just a slip up, because the rest of the explanation was correct.

New Video:
At about 7 seconds I refer to the angular momentum from gravity. It would be more correct to say “the angular momentum change from gravity.”
Also The R’s for the radius of the axle of the wheel and the radius of the wheel have been labeled incorrectly in the formula. ‘R’ refers to the radius of the axle and ‘r’ refers to the radius of the wheel.
3:59. I make an error about the unit of time and it held ‘s’ seconds and not second inverse ‘s^-1’
#9) Conner, Timmy, Kat In our video we tackle the concept of Reference Frames. As an example, we tossed a tennis ball directly upwards through a sunroof while in a moving vehicle, travelled at a constant speed, and caught it again through the sunroof. While this scenario looks completely different to the stationary observer and the tosser of the tennis ball, we explain that difference in observations is only due to their relative motions, their Reference Frames. UPDATED VIDEO
Well done. However, note that Timmy doesn’t see himself moving, so there should only be one car in his reference frame with the ball going up and down. There should be two Kats going by him. Additionally, it would be great if you could explain why the curve is parabolic and not just round. Additionally, you could trace the path of the ball and one could see it is in fact parabolic.

Below this line is Spring, 2016 By Friday of week 5, each group twill post a short statement about their project. Please find below a template that each group can replicate. Just hit “edit” above right, write down the project you want to do, and then hit “save”. #1 Mackenzie Haller, Joe Anderson, Omar Dominguez. We will investigate the mechanics behind the rotational frequency in an ice skater when they draw in and out their arms. We will replicate this by using a spinning office chair. We will use the dynamics lens. OK #2: Chad Collins, Saraith Aispuro, John Michael. We will conduct analysis on the effects of friction of various surfaces on the acceleration of toy cars of different sizes. Our primary lens will be dynamics, however we will also include discussion of each of the other lenses. OK: t is important to note that the coefficient of friction that you found is only a lower limit. In order to find the coefficient, you must push it until it slides. I think the most interesting example was the ice. It’s a pity you didn’t try your best with the ice example. 0:46 Predict the order (from lowest to highest) of the work of friction done by the car on each surface a) ice, cardboard, sandpaper, foil b) ice, foil, cardboard, sandpaper c) foil, ice, cardboard, sandpaper d) foil, ice, sandpaper, cardboard 1:39 What is needed to find the force of friction? a) the normal force of the car in the x direction b) the vector sum of the forces in the x direction c) the vector sum of the force in the y direction d) acceleration in the x direction of the car 2:46 What lens should we use to solve for work? a) dynamics b) energy c) momentum d) kinematics 3:25 What changes in the process for the other variables? a) solve for a new acceleration first b) change everything but keep the same acceleration c) solve for coefficient of friction first d) change everything but keep the coefficient of friction #3 Maxwell McCollum, Gabriella Santiago, Juan Gonzalez, Hannah Bulosan. We are going to investigate the changing energy in a system by using the energy from a spring to push a ball up and over a hill. We will be discussing and analyzing the different forms of energy throughout the experiment. our materials include: a spring, a ball, a track, a video camera, and a measuring stick. OK. My only concern is that you didn’t really consider what the spring constant was… if it was reasonable. If you consider the units to be N/m instead of Kg/s^2, you can ask yourself if you’d need 300N to compress the spring a meter, or 30 N to compress it 10 cm. I think it would be a great idea to actually measure the spring constant directly by pushing on it with a scale. For your T= 4:10 question, it is important to note that the moving of the track certainly does turn some kinetic energy into heat. If you had three loops instead of one, you’d find that the ball would not go as high at the end. T = 0:50 If we assume the roller coaster is a perfect and frictionless system, then what becomes of the potential energy of the spring? a) It is lost into thin air b) It is partially converted into KE and heat c) It is completely converted into the final PE when the ball reaches the top of the ramp Answer :C T = 1:25 How would we describe the energy between points 2 and 4? a) KE only b) KE + PE c) PEspring + KE Answer: B T = 1:31 Note: mass is a known a) Okay got it b) Move on Answer: Both T = 3:53 What are the units of K? a) There are no units b) Newton*meters c) Hertz/second d) Kilograms/second^2 Answer: D T = 4:10 Notice that when the ball moves through the roller coaster the track wobbles. Why is that? Should we use a new lens? a) In the real world the system is not perfect. When the ball rolls down the track, it applies a force against the track. Because forces are equal and opposite, the track recoils and pushes back against the ball. And because the track is not sturdy enough, the track wobbles. b) Lenses are for schmucks c) When the ball moves through the track, the track is absorbing some of that energy. d) There was a draft Answer: A T=4:35 Solve it yourself! What did you get? a) 9 kilograms/ second^2 b) 142.5 kilograms/second^2 c) 5.7 kilograms/second d) 285 kilograms/second^2 e) Avogadro’s number Answer 😀 #4 Kylie Altman, Brad Davis, Mackenzie Grossgold, Aashrita Manjunath, Ashley Martinez, Thomas Fuentez We will calculate the spring constant of a spring using 3 different masses by measuring their displacements and taking the average of the three results. We will also observe conservation of energy by using a pendulum with varying masses and lengths to predict velocity and the final height at the end. Both can be illustrated with graphs. OK. I have two observations: 1) You found that mass didn’t matter for the speed of the bottle. However, you presumed this to begin with by calculating the speed by using equations that allow mass to cancel. If you want to state that we can see mass doesn’t matter, you need to actually measure the speed by some direct means. 2) You finish the video by stating that you were accurate. What does this mean? I think you got very different measurements for your spring constant using the two different masses. Is this correct? This doesn’t mean you are wrong, it just means that you spring constant isn’t constant. It would have been interesting to make a F <=> x graph to see the shape. Let me know if I am wrong about either of these statements. #5 John Theofanides, Rogan Wells, Manny Gonzalez, Joseph Szillinsky, Jake Navarre (M-R 4-5) Video 1: We will be dropping an exercise ball from the Rec Center. In this experiment we will calculate change in Gravitational potential energy and kinetic energy. We can also find force, type of collision, and momentum transfer. Video 2: We will find the coefficient of friction, with the dynamics lense, of brakes on a bike starting at a constant velocity using the change of acceleration in the time it takes to get to a velocity of zero and distance traveled in that time. Video Links: OK: I like that you calculated some things from your measurments. However, it would have been nice to check to see if the calculations are correct – if physics really works. In particular, you calculate the speed of the ball when it hits the ground. Why didn’t you check to see if your speed was close to the slope of the displacement – time graph? It seems from the 60% loss that basketballs are not as elastic as one might think. OK. I don’t think that the coefficient of friction was low because of surface area… surface area should not come into play. I think part of the reason it was low was that the full coefficient of friction was not used… he didn’t skid on both tires. This would have been rather dangerous. The full coefficient of friction is realized only when it is exceeded. The coefficient you calculated was reasonable. Did you notice that your acceleration and coefficient of friction have the same number. Can you show yourself why this is not a coincidence? #6 Reven Wen, Jason Gong, Yawen Deng. We are going to analyze the mechanical process of playing the pool. We will use the lens of momentum and dynamics. We will collect data of the mass of the billiard balls and cue, the distance and the time of the movement. We will calculate the force generate from the cue and the velocity and acceleration of the balls. We will compare the results and find out if momentum is conserved. There are somethings I’d like changed in this video – you can submit these changes to me on a piece of paper rather than making the video over. Most importantly, momentum is a vector, and you need to add momenta as vectors… nose to tail and take the resultant vector – or you can just add them component by component. Also please provide a direction when you talk about momentum. You also talk about the force of the pool cue, but the better lens for this problem of collisions is one of momentum because we don’t really see the acceleration because it happens so fast in the collision. These collisions are not perfectly elastic (as none are), but they are certainly not perfectly inelastic. They are closer to being elastic than inelastic. Momentum is conserved in all collisions as long as there is not an outside force. You are right in observing that there is frictional forces involved so the kinetic energy will be lost and each momentum will decrease in magnitude over time. 1.If momentum is always conserved, why our calculation for the momentum is not conserved? Video time=2:02 (right answer is b and a) a. calculation error b. we didn’t count the momentum of the table and earth c. friction d. I have no idea 2.Is energy conserved? And why? Video time=2:46 (right answer is d) a. yes, because energy is always conserved b. no, because some of the energy disappear c. yes, because it’s physics d. no, because there is friction 3. Which one of the diagram is wrong? If there is a mistake, explain why. Video time=3:22 (right answer is a) a. upper b. lower c. both d. neither #7 Eitan Simler, Harrison Masters, Parker Smith We will drop a mento into diet coke and measure the velocity of the liquid as it comes out of the bottle. Next, we will calculate the acceleration of the liquid. Finally, we will determine the potential height that the liquid could reach using the energy lens. OK #8 Austin Frey and Andrew Meza We are going to bench press on a flat bench then on a decline bench and compare the work/power it takes to lift the weight. Using the energy lens we can determine the work/power it takes to lift the weight and compare them to see how they differ. OK, I like how you used Tracker. I wish you would have used the tracker data! You state that the force of the lifter’s arms > that of gravity, but you give the wrong reason – not because he lifted the weights upward, but WHEN he accelerated the weights upward. You could have used tracker to find that acceleration and then calculate the extra force necessary for this acceleration and found the total force the lifter’s arms must have put out…. for your next video. #9 Using a Spring to find the Velocity of a Car Xavier Caldera, Haley Garrow, Wesley Kao, and Jaspreet Mand By using a cart, a track, an elastic band or a spring, we can find the spring constant of the rubber band and the coefficient of friction to ultimately determine the velocity of the car at a given displacement. We can use dynamics and energy lenses to examine the energy transfer from the elastic to the cart, and ultimately find the velocity of the car. OK, I found this video to be particularly good: 1) You explained the physics extremely well (in my opinion) 2) The sound and visuals were clear, and the pictures were great as were the super smiles! 3) You calculated what one would expect to find, and then measured it and discussed how close you were. It’s worth noting that your discrepancy is more than explained by the uncertainty in the angle of elevation in calculating your coefficient of friction. Given that the angle could have been off by 1/2 a degree, you might expect an uncertainty of 25% in your coefficient of friction…. so this is well within what we might expect. What lens/lenses would you use to solve this type of problem? TIME: 20 sec a) *Dynamics b) Momentum c) *Energy d) Kinematics e) I will just plug numbers into formulas first What is the energy story? TIME: 23 sec a) The potential energy of the spring is converted to kinetic energy and potential energy of the car b) The potential energy of the spring is converted to just the kinetic energy of the car c) *The potential energy of the spring is converted to the kinetic energy of the car and some energy is lost to heat. d) PE(spring)=KE-Q e) *PE(spring)=KE+Q f) *PE(spring)-W(friction)= KE(car) How would you find the spring constant using this data? TIME :35 sec a) *Graph Newton’s over displacement b) Newton’s times meters c) Meters over newton’s d) Not enough information What are the forces acting on the car when it’s stationary? TIME 1:02 sec a) Normal, gravity b) *Normal, gravity, friction c) Air resistance d) *Sum of the forces is zero Why do we split the force of gravity into the parallel and perpendicular components? TIME 1:31 sec a) *Because the perpendicular component of gravity is equal to the normal force since the car is not accelerating in the y-direction b) *Because the parallel component of gravity is equal to the force of friction since the car is not yet moving which will help us find the coefficient of friction * indicates correct answer #10 Egg Drop Ariana Haghani, Nick Miller, Emily Mobley, Logan Turner We will measure the amount of energy it takes to break an egg by dropping the egg on different surfaces (concrete, dirt, and grass). We will drop the eggs from the minimum height required for them to break, depending on the surface, to calculate the amount of energy initially required to break the egg dependent on the surface we drop it on. Play posit questions: Time 0:25 What lens would YOU use to find the final velocity of the egg? a) Kinematic b) Dynamics c) Momentum d) Energy Time 1:35 What is the energy transferred to after it goes from PE to KE? (answer b,c) a) energy stays as KE after collision b) energy is transferred as heat upon collision c) heat energy is transferred to IR radiation d) energy is transferred as work done by Nick (egg dropper) on the egg Time: 3:22 What’s the final velocity of the egg on the 2nd surface? a) 2.5 m/s b) 5.2 m/s c) 55 m/s d) 0 m/s What is gained in the eggs collision with the ground? a. Heat b. momentum c. A cracked egg OK, I think what you’re saying is that the eggs break at the same pressure or Force/Area. The grass spreads the force over a larger area, so it can provide a larger force without breaking the egg. Also, this force is spread out over a longer time because the grass bends. So even a same force would absorb a greater impulse because the delta time is larger. #11 Amber Sucich, Garrett Lamoureux, Rob Maes, Austin Gandler We visited a skatepark to do a physics experiment on a halfpipe using the energy and kinematics lenses. OK, You realize that you found the average acceleration at the end. Because you are going up and down a curved surface, the acceleration was constantly changing. For instance, when you were up on the wall, the acceleration was ~ -10 m/s^2 directly downward because you went up and down a vertical wall. Thanks #12 Makenna Glisson, Giannine Escobar, Marissan Statner, and Nick Alder We are going to let 2 different objects go down a slope and collide with an object at the bottom, calculating the difference in friction and how that effects the momentum in the collision. We will be using the momentum and dynamics lenses. A diagram of our project can be found on: file:/C:/Users/Giannine/Downloads/physdiagram.pdf I really liked aspects of your video. I like how you got into trouble with the coefficient of friction and then realized that there was rotation. However, there were a few problems that I’d like you to address in a paper with all your names on it. Please do this as a group: 1) Most basic and important: you decomposed gravity incorrectly. Please do it correctly and explain why it was incorrect and show how you get the correct normal force from it. In your case, for a 2 degree angle, it doesn’t matter so much, but conceptually it is very important. 2) Please take the sound track out of the video and repost it. Or at least lower the volume. I can’t hear Marissa for a good part of the presentation. 3) We will study the subject of rolling today… as you may have seen in the videos. It may be best to look at this through the energy lens. However, I really like how you used the dynamics lens. Hopefully, you will see that what you did was incomplete. The subject is very complicated, especially with the skateboard that is partly rolling mass and partly not rolling. However, what you should know is that the coefficient of friction is an effective coefficient because there is no sliding between two surfaces. 4) I was not able to download your pdf. Please repost the link and/or make a direct link to the document. Because the problem is actually very difficult, I’m not asking you to correct #3, although I encourage you to explain why the skateboard has a higher acceleration than the ball. However, please do 1 and 2. Hand this into me as a hard copy that all 4 of you sign… and remember to ask yourself what is the direction of acceleration before you decompose your forces! T= :39 What is the normal force acting on the skateboard? A) 11.37 N B) 13.58 N C) 17.38 N 😉 D) 9.4 N T= 1:21 What is the normal force acting on the soccer ball? A) 4.71 N B) 2.68 N C) 4.20 N D) 3.92 N T= 1:25 How are we doing? A) Work work work work work work work B) Perfect! Teach me your ways!!! C) I have no idea what you’re doing D) WRONG! That is not the correct force of friction T=1:51 What is responsible for the turning of the wheels? A) Centripetal forces! B) Force of gravity C) Torque D) Normal force T=4:05 Why is the torque on the ball different from the torque on the skateboard wheels? A) It isn’t. You’re wrong B) The force of friction on the ball is larger than the force of friction on the skateboard wheels C) The force of gravity is stronger on the ball #13 Adam Lang, Jordan Young, Evan Ricaurte Using a speedometer-equipped bicycle, we will measure the stopping distance of the bike on different ground materials (grass, sidewalk, road, etc.) in order to find the coefficients of friction of these different materials using the Dynamics lens. OK, I myself would have used an energy lens: work of friction = kinetic energy. However, your way was great too. You would have simplified the math if you left the mass to be just m_o, then you would have been able to show that the coefficient of friction is just the acceleration divided by gravitational acceleration… no? In any case, this was very nice. 0:38 Which material do you think should be the best to stop on? (shortest stopping distance) a) Grass b) Asphalt c) Sidewalk d) Brick 1:57 After seeing these videos… a) It’s hard to tell which had the shortest stopping distance b) My guess was clearly wrong c) *If* skid marks were left this was an act of vandalism! 2:06 What Kind of physics problem is this? a) Momentum b) Energy c) Dynamics d) Kinematics e) Rotational Dynamics 2:34 By this statement Jordan really means… a) Evan is in equilibrium b) The vector sum of the present forces has a vertical component c) Evan has no vertical acceleration 3:55 Is equal to: a) Acceleration b) Displacement c) Average Velocity 4:05 “Simple Trigonometry” a) That’s ridiculous, you really mean using the formula for area of a triangle, 1/2 * b * h 4:14 Pause the video and try to find the time and resulting acceleartion for each material. Remember a= dv/dt 5:56 a) That sounds about right b) No way! F=m*a and F=mu*Fn can’t relate to the same force in a single problem 6:56 Was your guess about which material would be best to stop on right? a) Yeah! I’m great at Dynamics problems like this! b) No way, I was way off c) You guys are crazy, you clearly did something wrong here! Just think about it! 7:32 a) OKAY, now I believe you b) Nope, I just refuse to accept your results c) This was fun! d) I’ll be thinking about this next time I am on a bike! #14 Soccer Ball Hudson Deaton, Severin Elste, Ryan Rodriguez, Devin Williams We will be calculating the work done by a foot kicking a soccer ball into the air, and the energy lost (if any) during the elastic collision due to friction using the dynamics and energy lenses. There are some difficulties with the video I’d like you to correct. 1) I think that the average acceleration of the ball is much higher than 40 m/s^2. You don’t have to average in the zeros because the foot is not in contact with the ball at these times. 2) Please correct the statement that this is the acceleration after the foot is in contact with the ball… the ball accelerates due to the force acting on it, so it is accelerating while the foot is in contact with it, no? 3) Please calculate if the work you calculate is about = to the kinetic energy it gains. I’m sure you have access to the velocity of the ball. 4) You didn’t calculate the force of the ball correctly. You wrote that the acceleration was 9m/s. I think that maybe this was the speed before it hit his hands? The acceleration is certainly much higher… you’re saying that the force on his hands is less than the force of gravity on the ball? Does this make sense? You could use any number of means to calculate force… you could use rate of change of momentum, or mass * acceleration. However, please see from your graph that the acceleration is much higher than 9 m/s^2 (and please be careful of the units). 5) I encourage you to change the tracker data to show vector acceleration rather than absolute value. It should show that the acceleration is negative when it hits his hand…. you don’t have to do this if you don’t want to, but it would be nice. Please make these corrections, repost the video, and send me the new link. #15Skateboard Friction! Adriana Long, Molly Gaddis, Dimitri Popoff, Jeremiah Eseed While using the kinematics, dynamics, and kinematics lenses, we will be dropping a tennis ball, and a skateboard from the side of a skateboard park ramp to see the velocity they have as they go back and forth on the ramp. Then we will be able to see the change in energy, thus seeing the change in energy as the skateboarder goes across the ramp. Through this we can use Dynamics to calculate the coefficient of friction of the skateboard! OK, This was pretty good. You made one significant oversight. You really should have included more than just the 4 meters… which would have lowered the coefficient of friction even more, no? The reason: – You correctly point out that on the vertical surfaces, the normal force is very little and that the acceleration is downward. But if the acceleration is downward on these surfaces, it must be upward somewhere else because he’s not falling. Where is it upward? Thing centripetal acceleration, and you can see this would be at the bottom of the curved sides. Thus the normal force is considerably more than gravity there. However, your video is fine as is. 1:20 How do we know this? a) we can’t do this. b) the energy lens can help! c) change in energy= F x d ANSWER: b, c 2:18 Work= ? and what are the forces acting on this body? a) v x d b) F x d c) p x d d) Frictional force e) normal force f) gravitational force g) force of tension h) centripetal force ANSWER: b, d,e,f 3:11 What is happening to the normal force as he moves along the ramp? a) it stays the same b) It is the same as the force of gravity c) it changes, and is only = force of gravity when on the flat part ANSWER: c 3:56 The normal force when he is on the side of the pool is? a) greater than when he is at the bottom b) less than when he is at the bottom c) the same at both times ANSWER: b 4:52 Is this reasonable? a) Absolutely not! b) Are you crazy? c) I think so d) Yes, it is reasonable. ANSWER: c,d #16 Ellen Glad, Spencer Hayashi, Andrew Kwak, Mckenzee Sisson While using the Kinematics and Dynamics lenses we will be measuring the force that one group member gives another group member that is on a bike. We will use tracker to measure the distance traveled and time. With this information we can find the acceleration and then the Force used in the push of the human on the bike. We can also find the average power needed for this push. Physics on a bike OK, Good Video. If you look closer, you see that the acceleration didn’t start until about 0.1 seconds, meaning that she was only pushing you for about 0.9 s. This will boost the acceleration by 10% and the power by another 10% giving Mckenzee about 100W… we shouldn’t underestimate Mckenzee’s power! #17 Luke Matusiak, Miranda Miao, Kaitlin Bleich Using the dynamics lense, we will calculate the minimum velocity required to have a marble on a track successfully travel around a loop of a specific radius. While doing this experiment we must also account for the friction of the track, so our velocity will need to be just a bit higher than the math says it needs to be. Here’s our video OK, But you don’t really expect me to believe that you measured the height to a hundredth of a mm? This is certainly not necessary when you’ve already rounded gravity to 2% higher. There were some other statements that were not quite right. By finding the necessary speed at the top and calculating what the speed at the bottom should be, you are not including how it will slow down on the way down. Thus you really found the work of friction (and moving around) from the time you released the car at the top to the top of the ramp. Let me know if you think I’m missing something. In any case, I liked the video and it was well done. I like how you started with one idea and noticed a “problem” in the shaking loop, and decided to study the “problem”. Thanks Questions # Which lens(es) do you think are required to solve this problem? (After intro.) ## Dynamics ## Kinematics ## Energy ## Momentum ## How does one Physics? # Why do you think the shaking of the loop causes a loss of energy? (After intro.) ## Because while the ramp is moving, outward, it cannot apply a normal force. ## Energy from the car is transferred to the movement of the loop. ## Energy is not conserved. # Why is the normal force allowed to be set to 0 in the dynamics portion? (After the dynamics portion.) ## Gravity is equal and opposite to normal force which makes them cancel. ## Because the car does not accelerate in the Y, so no normal force is created. ## Because Luke said so. ## Normal force is always 0 in a Loop de Loop. # Where is there room for error in this experiment? (At the end.) ## Neglecting the friction on the ramp. * This is a good answer but hotwheels tracks have very little friction, most of the friction is found in the loop where the tracks change shape. ## Using the wrong experimental height. ## Nothing could ever go wrong this experiment is flawless and the scientists are the worlds best. #18 Jesse Chavez, Alex Medina Through the construction of a slingshot, we will be storing the energy through a spring and find the forces when the spring is stretched, providing some Tension. The force exerted by the spring would also turn the Potential Energy of the spring into Kinetic Energy. Through the use of tracker or tangible measurements, we could find the speed and the projectile direction of the object flinged. The lenses observed will be dynamics and energy. I don’t understand your calculation. Let’s talk when you can. #19 Dylan Kohler, Jordan Johnson, Jensen Severance We will use an energy lens to analyze how much energy is lost to heat when a skateboard’s wheels spin. Furthermore, we are going to analyze how different coefficients of friction affect a skateboarder’s kinetic energy. OK, thanks Questions (answers in bold): # Is this a good answer? (2:24) ## Yes! Everything looks good! ## Not quite! Why is the coefficient negative? # What can I do to fix this? (2:28) ## Take new videos and redo the tracker graphs ## Redefine the axis to make friction a positive force * This is what we did ## Redefine the axis to make gravity a negative force ## Panic * If you chose this, you’re not alone. We did this too, and plenty of it. ## Give up # Is there anything I can do to improve this equation before moving on? (4:09) ## No you’re good! ## Cancel * the masses can be canceled ## You forgot to account for normal force # Have you? (0:14) ## Nope ## It keeps me up at night ## I find it gripping # Quick! What’s the dynamics protocol (check all that apply) (0:52) ## Surrender ## Panic! ## Draw a picture ## Just plug and chug ## Is it in equilibrium? #20 Karson Slocum, Gracie Ponomaroff, Daniel Applin, Marcus Beloney, Isabella Paoletto We will be using the energy lens to analyze a golf swing. We will look deeper into the work put into a swing and how much energy is transferred into the ball. Please make this correction. In finding the energy in Marcus’s club, you used a mass of 0.45 kg. This is likely an overestimate because the speed of the shaft and handle are much less than the head, so it may be better to find the mass of just the club head. Then you use the final speed of the ball to calculate the final speed of the club, which is not the case. In fact, I think you can see when Macus hit the ball in the Tracker velocity graph. There is an abrupt drop in speed in the middle of a rise in speed. This drop in speed could be due to the impact with the ball. You should use these two speeds to calculate the loss of kinetic energy of the club. All in all, I don’t understand why you didn’t find the speed of the ball from the same video that you found the speed of the club. This would have given you two corresponding sets of data from the same event. I’d appreciate it if you could write this up and submit it to me. You don’t need to make another video, but you need to correct the calculation. #21 Torque in Two Static Systems Bryce Farrell, Jenna Stephens, Maiya Shoemaker I thought we already posted it, but we will be doing a project that has to deal with leverage, energy, and forces. We drop a heavy object onto a piece of wood that acts like a lever to propel something on the other end. Our main lens will be dynamics. OK,I find this video particularly interesting. You have found a way to make a scale from two objects that you know the mass of (the wood bar and book) by taking the measurements of lengths of moment arm in order to make it balance. 1. Time: 13 sec Which lens should we use to calculate Maiya’s force? a) Dynamics b) Kinematics c) Energy d) Momentum Answer: a 2. Time: 54 sec Keeping in mind positive direction, how should we add the Torques? a) Tbook + Tmaiya = Twood b) -Tmaya + Tbook +Twood + Tfulcrum = 0 c) Tmaya – Tbook – Twood – Tfulcrum = 0 d) -Tmaya + Tbook + Tfulcrum = 0 Answer: b, c 4. Time: 3:29 How does the mass of the wood affect the system? a) It doesn’t. We don’t need to worry about that! b) The force of gravity pulling on the wood will add torque to the system. c) The normal force of the wood will counter the force of gravity. Answer: b 4. Time 3:49 Where is the best place to set center of rotation? a) Anywhere. It doesn’t matter. b) At the left side with the crayon box c) At the fulcrum d) At the right side with the book Answer: c #22 Dane Mortensen, Michael Curtis, Emma Lang, Jared Gunsky, Emily Almeda, Raymart Ballesteros We will be analyzing the conservation of momentum as I ride on a skateboard, holding a ball, and throw the ball out in front of me. We will also be flinging a pail of water around on a string and explaining how to find the velocity needed to keep the water from falling out. Part 1 Updated: There are some changes we need in your videos. I would appreciate it if you could make these two videos again: The first video: how great does the tension in the string have to be in order for the water to not fall out of the bucket? Please prove this. Please do it and feel it as well. The second video: please calculate the speed of the ball from tracker and see how close you are. Please also show how you got a speed of 27 m/s from your calculations. Please also ask how fast this is and if it is likely that this is how fast the ball was. #23 Potato Launch Kendrick Nguyen, Steven Blakely, Evin Killian, Alfredo Aragon. We will be shooting a potato cannon into a pendulum and use the dynamics and energy lens to calculate the amount of energy that was transferred from the potato into the pendulum OK, fun video. I liked the error analysis that you did at the end indicating your uncertainty. However, I disagree with the words, “there’s no way to know how much…” I think you could have estimated the amount of potato lost and the amount of momentum that the potato took with it. Now a few comments: 1) You state that hitting the pendulum off-center introduces an error. We see from the Veritassium videos with the bullet that hitting it off center doesn’t affect the velocity of the spinning or nonspining object. So this is not a problem. 2) We don’t really have to worry about the energy that the potato takes with it when it blasts in different directions because we’re looking at the transfer of forward momentum. So the real question is if the potato took momentum forward or momentum backward with it.This is the momentum interaction. If the potato took kinetic energy with it by exploding laterally, then that doesn’t affect the forward speed of the pendulum. Additionally, knowing how much mass was lost would be helpful, but not crucial because the mass of the potato is considerably less than the pendulum. Now, looking at the video again carefully, you can see that the blast moves forward at about the same velocity as the pendulum. Thus the forward or backward momentum that it takes with it is very small compared to the initial forward momentum that it had. As the speed of the pendulum is way way small compared to the original speed of the potato, this consideration is negligible. 3) It’s a pity you didn’t fire it off at a 45 degree angle and see how far it went to estimate the speed a different way to see if it was close to the same. 87 m/s… is that fast? Might you reflect on that? All the same, it was a fun video and reasonably done from a physics perspective. #24 Alexa Schure, Connor Cody, Connor Miller, Cole Ballinger Pool Ball Project We will be dropping a ball down an a sloped surface (a halfpipe) and calculating both the Kinetic and Potential energy of the ball as it rolls across the surface. We will use this information to make a potential energy graph. We will also be rolling the same ball down a small hill to have it collide with another object so we can calculate the the energy before and after. Our main lenses will be Energy and Momentum. Kinetic energy can only be positive regardless of direction, so you don’t subtract initial kinetic energy if the two balls are moving in opposite directions. If you want to conserve momentum in a collision, then the direction matters. You had an interesting mix of problem solving in this, but the multiple problems made it very difficult to stay consistent. I like how you find the loss of kinetic energy, and I like how you find the work done by friction. However, it would be very nice if you could compare the two. I suggest that you just take one single collision and analysis it with respect to momentum, energy, and the work done by friction especially if one of the balls rolls to a stop. Below this line, Winter 2016 Videos. Please put Spring 2016 videos above this line. #1 Baseball, Carolina Cleland, Alec Fuoti, Maxwell Ngo, Matt Walker, Luke Breazeale, We will investigate the kinematics involved in different trajectory patterns of a baseball. This was very well done! You know you could have simplified the process by finding the total time to go up and down in one step, but I totally liked the way you did it. #2 Ren Yee, Eric Chang, Deric Van Damme. Using Dynamics, Energy, Momentum and Kinematics. A person on a bike is pushed and has a collision with a suspended water bottle. Caculate change in energy and find coefficient of friction. The mass the bottle <<< mass of Ren, so there is almost no energy lost when she hits it. This has nothing to do with it being elastic or inelastic as you state around 20s, no? You are trying to find the coefficient of friction, but this is rolling friction – she is not sliding, so there is no slippage between her tire and the pavement, so it is not correct to find a coefficient of friction this way. At 3:16, you state that the Force of Derek, but I think you mean the work he did, because it is in Joules? Please make the appropriate edits. It may be a good idea to drop out the collision, and just look at the work in and the change in kinetic energy. You may want to develop it more by describing how you got the force of Derek, and also describe what rolling friction is. Maybe what you’re finding is the coefficient if rolling friction? #3 Anisha Datta, Kira Deguchi, Daniel Faktor, Taylor Cardinale: To find the coefficient of friction of an inclined plane on which a calculator slides down and the angle at which it starts falling. OK. Well done and easy to understand. You might explain again at the end why F(friction) = mg*sin(theta) is because at the moment the static friction fails, acceleration ~0. But OK as is. #4 Analyzing Force, Work, and Power in the shot of a Basketball : Andre Viloria, Joshua Viray, Ryan Staples, Carsten F, Using a multitude of lenses, we will investigate the work and power of shooting a basketball, and how data differs among each member of group. At 1:50 you say you use the dynamics lens, but there is mostly talk of work and energy. But no worries. There is a problem in your calculation of power though, because you say that the force is just the force of gravity, so the work you calculate for him is just the potential energy he gives the ball when he pushes it upwards, but it also gains kinetic energy. His arm is greatly accelerating the ball, and you should consider the change in potential energy + the kinetic energy gained. So the work and energy and power you calculate is way too low. For the 3-pointer, how did you get the force to be mass * velocity? Where did 15 m/s come in? And 30 m/s^2 for the half court (good shot). The video, audio, and graphics was spectacular. However, you need to do the power calculations over… at last one of them. [1] Time: 00:22, What lens should we be looking for through to find work of the shooter’s arm on the ball? A) Energy B) Dynamics * C) Angular Momentum D) Kinematics E) Momentum [2] Time: 00:37, What is going on in the video? A) The energy the shooter puts into the ball is transferred to kinetic energy of the ball. * B) Some of the kinetic energy of the ball is transferred to potential energy at the top of the curve. * C) The kinetic energy of the ball is lost to gravity D) The kinetic energy of the ball is lost to the net [3] Time: 00:51, Why do the graphs look so disjoined for the free throw shot? A) The shooter should never go pro. B) Gravity was stronger at the top of the curve. C) The ball was shot improperly. D) The ball hit the rim before going in. * E) The air resistance was not constant due to a gust of wind. [4] Time 02:14, What needs to increase for the three point shot compared to the free throw shot? A) Acceleration * B) Mass C) Work * D) Power * E) Friction [5] Time: 03:50, How does the work compare between the shooters of the basketball when they go further away from the basket? A) Work of the shooter at free throw line > work of shooter at three point line > work of shooter at half-court. B) Work of the shooter at free throw line < work of shooter at three point line < work of shooter at half-court. * C) The work of all three shooters is the same D) There is no work being done in any of the systems E) Not enough information given #6 Sidney Stefani, Mel Gavin, Ethan Angold. We will use the momentum lens to investigate a collision between two billiard balls, confirming that momentum is conserved, evaluating what would happen in an elastic and inelastic collision. Looking at this collision from an energy lens, we do not know that kinetic energy is conserved. This collision was a partially elastic collision, Meaning some kinetic energy was transformed into heat. The reason we used the momentum lens to analyze the initial and final velocities is because we do know that momentum of the system is being conserved, but kinetic energy might not be. (0:11) When analyzing this collision, we will treat the two balls as if they were sliding point masses on a frictionless surface. (0:34) Not knowing the masses of either ball, consider what would happen if the balls stuck together when they collided. Which of these are reasonable final velocities for the two balls after the collision? a. 0 b. 0.3 m/s c. 0.5 m/s d. 0.99 m/s e. 1 m/s (0:49) What lens is the most useful to analyze this collision? What is conserved? a. Energy lens, because Kinetic Energy of the system is conserved in the collision. b. Energy lens, because Total Mechanical Energy of the system is conserved in the collision. c. Momentum lens, because Momentum of the system is conserved in the collision. d. Dynamics lens, because one ball exerts a force on the other ball, causing it to accelerate. (3:30) So what is the total momentum in the y direction of the system? a. 0 b. 1 kg*m/s c. -1kg*m/s d. not enough information (4:21) Then how can each ball have a final vertical component of velocity? a. They shouldn’t. There must be an outside force on the system we are not considering. b. Because we defined a positive and negative direction for y, we can say that the final vertical momentum of one ball s equal and opposite to the momentum of the other, so the momentum in the y direction of the whole system is still 0. c. There is an invisible third ball. d. Pushing the ball with my hand caused there to be momentum in the y direction. Please send me an Email indicating when I might expect to receive a link for your video. #7 Krystall Romero, Christine Prothe, Uriel Nieves-Cruz, Paige Alford. Calculating the final velocity of a nerf gun bullet using kinematics. 1. 58 seconds- Using Vx and Vy, what should the initial velocity be? *a. 15.7 m/s b. 9.1 m/s c. 20.2 m/s d. 8.3 m/s 2. 2.15 s- Is this time possible with this velocity? a. yes *b. no c. I don’t know 3. 2.24 s- Which of these equations give you time? *a. Δy=VyΔt+1/2at2 b. V=Vo+at c. X=Xo+vt This is done correctly. In looking closely at your video, I think that the problem came not because you measured time wrong, but because you measured the angle correctly. If you look at the video carefully, I think you see that the angle is less than 30 degrees. Please do this and see if your calculations now make sense. You don’t have to redo the video thought, because it’s OK as is. #8 Miranda Salo, Michelle Wong, Travis Lang, Jodie Yu. Using momentum to investigate the speed at which a door closes in an inelastic and elastic collision using an elastic ball (bouncy ball), and a inelastic ball (clay ball). at 4:14 you say, “all the kinetic energy of the clay blob is absorbed by the door. I think most of the kinetic energy is turned to thermal energy. You may have meant to say, “the momentum of the clay blob is shared between the clay blob and the door”? I liked the actual demonstration. I think that the boards of algebra was difficult to sit through… The sound and visual quality was pretty bad. I think having someone hold the camera is a bad idea. All in all, good. Video Link: Questions: 0:27–Knowing the 2 types of collisions, what lens would you use to solve this problem? a) dynamics b) kinetics c) energy (Correct) d) momentum (Correct) e) energy 0:43–To solve for the final velocity of the door, and using the energy and momentum lens, what equations would you use to relate the two? a) F=ma b) KE=1/2mv*2 (Correct) c) T=Fr d) p=mv (Correct) e) PE=mgh 4:10–To solve for the final velocity of the door in the elastic collision, which lenses should you use? a) dynamics b) kinetics c) energy d) momentum (Correct) e) you can”t 4:55–What is the relationship between the two equations? a) v(inelastic) = v(elastic) b) v(inelastic) = 1/2v(elastic) (Correct) c) v(inelastic) = 2v(elastic d) Who knows? 7:30–What is the relationship between the mass of the ball and the velocity of the door? (for both elastic and inelastic collisions) a) inversely related – as mass of the ball increases, velocity of the door decreases b) directly related – as mass of the call increases, velocity of the door increases c) no relationship – the mass of the ball has no effect on the velocity of the door d) not enough information ====#9 Lou Sugo, Neil O’Keefe, Kayla Londono, we went skydiving and will be tracking the kinematics of our free fall using the dynamics lens.==== ==== ==== ====Video Link: __ This has beautiful graphics and sound track. What a lovely adventure! Also the video quality was well done. However, there are a few mistakes. The reason the acceleration decreases and goes to zero is because you are going faster and faster and the air resistance increases with speed. The increase in air density is a tiny part of that. Air density increasing is what causes your speed to actually decrease just a little as you fall. The other problem is I’d like you to look at your displacement graph. What’s wrong with this? How do you see velocity on the displacement graph? Also, please finish the video, even if it goes a little over 5 minutes.


2:10—- Why is the average acceleration -2m/s^2 rather than -10m/s^2? Choose all that apply

a)we are over the ocean and gravity isn’t as strong

b)air resistance

c)we did our calculation wrong

d) the density of the air is changing

2) 2:36 —- Are we in equilibrium?

a) Yes, we are ALWAYS in equilibrium

b) No, we are NEVER in equilibrium

c) at certain times in our free fall we are in equilibrium and other times we are not

3) 3:44—- What is terminal velocity? Choose all that apply

a) when there is no acceleration

b) when you spontaneously combust

c) when the air resistance is equal and opposite to the force of gravity

d) the highest velocity you reach during free fall

4) 4:26—- Does the average acceleration we found earlier make sense now? Why?

a) No, your idiots

b) No, the acceleration is -10m/s^2

c) Yes, because we hit terminal velocity after 15 seconds

5) 5:00—- Do you want to go skydiving now?

a) Hell no!!

b) if you pay for my very expensive 31 seconds of free fall

c) Sign me up!!!

#10 Caleb will analyze the flight and stabilization effects of different P.I.D. settings on a home built quadcopter. This will look into dynamics and energy. Video Link: This was good. #11 Jackie, Cassi, Samantha, Madi. We will investigate the changes in kinetic and potential energy of a person swinging on a swing And how this is related to an applied force. good job…. I don’t think you ignored the potential energy in the middle, but rather you assigned it a hight of zero there, and thus you defined the potential energy at that point to be zero. (:10)What lens should we use? dynamics kinematics *energy momentum (:58) If Jackie were to have let go of Cassi at the height of 0.23 m, what would Cassi’s final potential energy be? *same as the original potential energy same as the kinetic energy at the bottom energy is lost to gravity a&b (:59)Is energy conserved? no most is lost to heat energy is always conserved *energy lost to heat isn’t significant so we can assume that mechanical energy is conserved (1:45)How do we use potential energy to calculate work? you can’t *we know that U initial + Work = U final you have to calculate KE First (3:51)Is this a reasonable force? *yes; the average force to push a person is about 300 N to 600 N no; this force is much too big no; this force is too small to push a human *yes; Jackie pushed her lightly #12 Malcolm Smith, Jacob Sands.Using our knowledge of projectile motion, we will analyze a bmx bike going off of a jump. (questions in video description on youtube) You don’t know the angle to 4 significant figures, so it’s best to round to a number that you have confidence in. You find the kinetic energy in Joules, to find the height, but didn’t need to. You could just fill in the mass to get the energy in order to get the height. You could have just canceled mass and solved for height. But That’s fine, no worries. Your last slide is wrong… just a mistake. You state “vertical direction” when you mean “horizontal direction”. The thing that is lacking is that you calculated what the maximum height should be and what the horizontal displacement should be, but you didn’t check how close your approximations are. You have the data in the videos, please check to see how well your calculations agree with the video displacement data. #14 Johnny, Callie, Felipe, Dalton. We will use the momentum lens to investigate the types of collisions between billiard balls. At 36 seconds you say that elastic collisions are where the first ball transfers all it’s kinetic energy to the second. Is this really true? What if both balls are moving? what if one is bigger than the other? What does elastic mean? Also, the cue ball going backwards after the collision… what does that say about the amount of momentum transferred to the other ball? OK, good enough. Question 1: What’s an inelastic collision? Click all that apply asked at 0:30 -when both objects stick together after colliding* -when both objects go off in different directions after colliding -when both objects stop at the point of collision -when energy is transferred from one item to another Question 2: Is momentum conserved when one ball hits another? asked at 2:06 -yes- momentum is always conserved!* -no- momentum is never conserved! -no, momentum is not conserved in this instance! -Yes, momentum is conserved in this instance! Question 3 Why is the measured velocity different than the calculated velocity? Click all that apply asked at 2:44 -the ball decelerates instantaneously -the balls do not fully transfer their energy and that is apparent because you can observe the balls moving after the collisions* -energy is transferred from the collision due to heat* -the second ball gains mass after the collision Question 4 What is V3? asked at 3:30 -0.7 m/s* -10 m/s -1.5 m/s -0.5 m/s #15 Rhett, Morghan, Stephan, Nick, Amanda. We will be finding the coefficient of friction of the concrete in a half pipe in the SLO skate park. We will use a energy lens and the negative work done on a block of ice. Here’s our Video: Do you really know your energy and other values to 4 significant figures? The presentation struck me as kind of subdued. Maybe you could reflect on if this coefficient of friction is high or low? In fact, it’s really not a coefficient of friction, because if it were really about 0.3, it would imply that at 15 degree inclination, the cube wouldn’t slide, but we know they do. So it’s really an issue of viscosity of the water later under the cube I think. In any case, the calculation and experiment are very novel, so I like that. It’s good. # What lenses would help us think about the ice blocks sliding into the empty pool as shown? Check all that apply. (0:22) # Dynamics # Kinematics # Energy # Momentum # Pete’s glasses 2. What is true of the normal force and the frictional force as the block slides down the ramp? (0:43) # The normal force increases and applies a frictional force backwards # The normal force decreases and therefore applies a force of friction backwards # The block is made of ice and does as it pleases – no physics can help us here. 3. Sorry the writing is a bit small – this is a perfect opportunity to pause it and work it out for yourself! (1:30) # Yeah! Sounds interesting! # I’d rather not and just pretend like I did honestly. (shame) 4. Please note the sound of the microwave starting. Morghan couldn’t wait 5 minutes to make popcorn – please shame her for being so unprofessional. (2:00) # Shame on her! # Girl’s gotta do what a girl’s gotta do, popcorn is delicious. 5. Despite the popcorn noises, I hope you still solved for Force of friction on the ice block. What did you get? Continue shaming Morghan mentally please. (4:03) # 20.23 N # -16.42 N # -13.40 N # 2 Petes 6. Now solve for coefficient of friction! (4:37) # Coefficient of friction = .295 # Coefficient of friction = .650 # Coefficient of friction = .753 # Coefficient of friction = .013 #16 Calvin, Tim, and Ian. We calculated the Mu of grass using Tracker. You really were not measuring the mu of grass because you were not sliding on the grass. You were rolling without slipping. The force that slowed Tim down was the “negligible” rolling friction force you referred to in the beginning. This is why the coefficient you calculated was so small. Could you imagine sliding on a surface and slowing down as gently as he did? It would have to be a very slippery surface. Please correct this by looking up rolling friction or otherwise correcting the video. You can write it up …. In the beginning in identifying forces, you neglected the normal force, but I think this was just an oversight. 00:22 The only thing that does work on the bike is… a.) The force of gravity b.) The force of friction from the grass c.) Tim pedaling backwards d.) Tim falling off 00:44 What are a few negligible forces? Choose all that apply a.) air resistance b.) gravity c.) friction from the ball bearings d.) lift 2:23 What is the normal force of Tim and his bike? a.) 420N b.) 784N c) 867N d.) 1N #17 Nina, Jared, Nick, and Jonathan. We are going to test how much more work is required to push an everyday object (like a lawnmower) instead of pulling it. We also plan to find the energy lost to heat and the coefficient of friction. Video Here! I’m curious what was the train wreck. You really didn’t measure the coefficient of friction because you were rolling. Maybe it was an effective coefficient of friction. I think that you overestimated the acceleration. I think the acceleration was close to zero in the first case, which would have given you a much higher effective coefficient of friction. Jared is very comfortable in front of the board and camera – you will take my place sometime. Video is OK. 18 Luke Wathen, Paul Sutton, Spencer Grenley, Jacob Winter. We are going to measure and calculate how a slack line reacts to the force of gravity acting on a body and, in turn, acting on the slack line; we will find the force of Tension. Video Link: OK #19 Averil, Taylor, Jason. We are going to calculate the energy lost and other variables involved in the collision of a handball with the wall. Video: OK (1:05) How was velocity equated? # A. d/t^2 # B. d/t # C. .5at^2 (2:35) How much force did Averil exert on the ball? # A. 7.05 N # B. 3.5 N # C. 10.0 N (3:25) How much power was exerted? # A. 89.06 J # B. 89.06 W # C. 95.50 W (4:10) How much work was done? # A. 5.97 J # B. 6.50 J # C. 10.0 J (4:22) What lenses did we use in the video? # A. Dynamics # B. Kinematics # C. Momentum # D. A&B # E. All the above #20 Noah Fisher, Eric Lopez, Naea Oda, Tai Stratton. We are investigating the physics of the game Spikeball by calculating the spring constant. Link to video OK #21 Brandon Perez and Jarrett Shirouzu, Mechanics of a Pitch Be careful, you mix up the dot product from the cross product. Some of your statements related to torque don’t make sense to me. It’s OK Below This Line, Fall 2015 Videos #1 Angular Momentum, Karate, Ice Skating, Pete Schwartz, Gary Schmidt, Yuna Kim. We will investigate the equation: Torque = rate of change of angular momentum, and how this relationship crucially important if you want to execute a good wheel kick, or vault yourself spinning in the air. #2 Trebuchet Analysis, Billy Gottenstrater, Garrett Watson, Sukhman Marok, Stefan Denny. We will investigate the various components acting within a trebuchet, as well as the acceleration and trajectory of the projectile. Are you going to make one too? Not necessary, but you could analyze the motion with a video. Yes, we will be constructing one and analyzing its motion using tracker. There were some mistakes in the video. However, I liked the fact that you built this and did the analysis so much, I assigned this video for Tuesday. Thanks Video: Video on Educanon with questions Video Questions: * denotes the correct answers. TIME: 0:17 Question: Select all that are true. *A) A trebuchet works by using the energy of a falling counterweight to launch a projectile. B) The projectile experiences centripetal force when launched. *C) To maximize the launch speed the counterweight must be heavier than the projectile, in order for the counter weight to fall quickly. *D) The projectile experiences centripetal acceleration when launched. TIME: 1:58 Question: What would happen to the initial PE and KE if the velocity was doubled? A) PE would stay the same and the KE would be doubled. B) Both PE and KE would be doubled. C) PE would stay the same and the KE would increase by a factor of 6. *D) PE would stay the same and the KE would increase by a factor of 4. TIME: 3:23 Question: Now that we have total amount of torque applied over time, how to we find work? a) (Total torque)*(distance) b) (Total torque)*(change in time) *c) (Total torque)*(change in theta) d) (Total torque)*(radius) TIME: 3:56 What would increasing theta do to the perpendicular force? What would decreasing it do? *A) Increasing theta will increase perpendicular force. Decreasing theta will decrease perpendicular force. B) Increasing theta will decrease perpendicular force. Decreasing theta will increase perpendicular force. C) Perpendicular force will remain constant no matter what theta is. D) Not enough Information. #3 Momentum Cannon, Luke Thompson, Luis Verastegui, Zac Powell. We will analyze the conservation of momentum and transfer of energy from a series of elastic collisions caused by dropping a set of rubber balls from a given height. Video Video on Educanon It would have been a good idea to say, “this is the picture immediately after the big ball hits! at the beginning. Also, I liked how Zac checked the momentum afterwards, and it would have been nice to do the same for kinetic energy. VERY nice consideration of the lack of perfect elasticity. The several videos of the drop was an excellent touch (in my opinion). All in all, super! Questions: At 0:20 Pay attention! We will have you follow along doing the math for a 2 meter drop (as compared to our 1 meter drop). At 0:40 Q: Why are we ignoring Gravity? Because * 1) The colision takes place so fast that the affect of gravity is neglegible. 2) Gravity does not affect the 2 masses since they are falling together 3) Gravity is not really important and doesn’t ever do anything 4) Gravity is always conserved At 1:10 1) In the corner you can see where I Derived the velocity based on a one meter hight and I used that to find the momentum of the system. Now find the velocity of the collision if it was droped from 2 meters: 1) 4.5 m/s 2) 4.5 m/s^2 3) 10 m/s^2 *4) 6.3 m/s 5) 6.3 m/s^2 At 1:15 Q: What would be the momentum of the system if it was dropped from 2 meters? 1) 1.53 kg*m/s 2) 3.06 kg*m/s *3) 2.14 kg*m/s 4) 2.64 kg*m/s At 1:33 Q: What would be the velocity of the system if it were dropped from 2 meters? 1) 1.7 m/s 2) 3.4 m/s 3) -3.4 m/s * 4) 2.38 m/s At 3:55 Q: How high will the small basketball go if the whole system was dropped from 2 meters? 1) 3.35 m *2) 3.91 m 3) 4.23 m 4) 6.70 m 5) NEI At 4:03 We meant to say ‘Elastic,’ but you knew that already. #4 Bow-ing to Physics, Desiree Pietrobono and Isabella Lew. We will be analyzing the energy stored in a bow’s string (Fspring= Kdelta X)– treating the sting as a spring. It is important to know the force capability of your bow if looking to successfully hit your target. Nice that you sped up the video during the writing of the formulas and then also added audio separately… that’s something I’ve never done… ah the beautiful cinematography! But how did you know that it took the arro 0.54 seconds to go from the top to the bottom? Did you stretch the string back only 7 mm? or was it 7 cm? You indicate 7 mm, which is responsible for there being such a low energy but a high spring constant. I have since received the following from Desiree: To find the time it took for the arrow to hit the floor from its initial point of release, Isabella and I entered our video into Tracker, created a point mass and assigned it to the tip of the arrow. We then tracked the arrow and analyzed the time graph to find that the arrow took approximately .54 seconds to reach the floor from its initial release point. Calculation Corrections When using tracker, we found that it took about .54 seconds for the arrow to reach its initial landing point from its initial release point. Because we know that the arrow travels in the x direction the same amount of time it takes for the arrow to travel in the y direction, we can say that the arrow traveled for .54 seconds in the x direction. We know that velocity in the x direction is constant, Vx(initial)=Vx(final), so we can then find the initial velocity of the arrow in the x direction by using the equation X=x(initial)+Vx(initial)(t). By calculating the range the arrow traveled in the x direction with simple measurements, we know that the arrow traveled in the x direction for .68m from an initial position 0. After algebraically manipulating the equation, we find that the arrow’s initial V=1.26m/s. (Kinematics we have an object changing position in a certain amount of time) Now that we know Vx(initial), we can use trig to find the sum of the velocities of the arrow when released at a 35 degree angel–cos(35)=1.26m/s/V(initial)=1.54m/s. To find the Kstring, we use energy because the PEstring–>KEarrow. 1/2K(dx^2)=1/2m(V^2) K=((m(V^2)/dx^2) When dx=.07m, marrow=.005kg and V(initial)=1.54m/s, K=2.42 N/m PEstring=Wstring=Energy stored in the string PEstring=1/2(1.6N/m)(.07m^2)=.0059 Nm or .0059 J. Looking back at the problem, it is very unreasonable for a string to have that high of a K constant when its potential energy is so low. End of her message. So this seems better to me now. 00:58 How much does the velocity change in the x direction after initial release? A) the change in velocity is proportional to the change in velocity in the y direction B) *it does not change C) its velocity decreases by 2/3 01:52 Why would we use trajectory to find a spring constant? A) *Because we can use the sum of the velocities to find velocity initial after point of release B)* Because energy is conserved C) Because the spring constant K is equal to the KE of the arrow in the x direction. 2:52 How much energy is stored in the string? A) energy is not stored in the string, but in the arrow B) *the inverse amount of work done on the arrow by the string is the amount of energy in the string C) *the amount of potential energy I hope you compare this stored energy to the kinetic energy of the arrow. You can measure this with the video itself knowing the number of frames per second. #5 Moon Shoes, Ariana Torres, Estela Miranda. We will investigate the energy given from then moon shoes. Jumping stilts might be better in any case, I hope you compare this energy with the gravitational potential energy of the jump. Interesting, although I would have liked to see some original footage with you guys on moon shoes. I didn’t understand some of the references to Newton’s 3rd law and how it pertained to what you were doing. However, maybe I just didn’t understand. In any case, your message was clear that moon shoes are not like walking on the moon. #6 Wind Turbine; Aryan Zaferani, Chad Zaback, Shayan Moghimi, Brent Hoekstra. We will calculate the amount of energy a specific wind turbine produces, we will calculate how many kW the generator produces from the wind. This is fine. You seemed to explain the math well. It might have been good to anchor your camera, as the image moves around. #7 They See Me Rollin’; Connor French, Heidi Pomeroy, and Toni Dematteo. We will investigate the equation: Linear Velocity = rotation / time * radius of wheel, and how this relationship can be used to determine how fast a wheeled vehicle is moving by simply looking at its wheels. I think you say in the video that v = dL/dt. However this isn’t correct. Your use of the second derivative is also incorrect. You actually calculate the speed correctly, but you don’t take any derivatives, and certainly not any second derivatives… you just use v = distance/time. several days later* I’ve just received a written reflection from this group: They have in their notes that v = dl/dt, where “l” is length… the length of the ark of the wheel (theta*r), but they refer to it as angular momentum. So their notes were correct, but taken out of context. It is a good statement of how dependence on a formula will make us vulnerable to many a misunderstanding and mistake! #8 Power of Power: Ryan Lau, Nick Ryan, Jade Jang. We are analyzing the kinematics of shooting a basketball from the 3 point line. The basketball undergoes free fall (the only force is gravity on the ball) so we know this is a projectile motion problem. Additionally we will connect the other mechanics lenses (energy + dynamics) for a deeper understanding of the classic projectile motion project. Sorry pete How did you start with 2 seconds for a time? Where did that come from? Please explain this in a written document… also a tangent of 3 seems more than what I see in the video. Why is this? They responded in an Email: “ I am sorry this response for our video project took so long. The reason we started off with an initial time of two seconds for projectile motion was due to our video analysis of projectile motion. The basketball, starting at when the ball first left Nick’s hand, had a travel time of about two seconds. We are sorry we did not clarify this value in the video. Furthermore, our drawings in the video did not accurately portray the final angle we calculated. Upon further reflection, we should have shown our clip of Nick shooting the ball one more time to show that the angle of about 70 degrees was accurate.” #9 Slippery Slope: VIDEO: Link on Educanon Griffin Johnson, Nick Adam, Michael McAniff, Sebastian Seibert von Fock. We will calculate the coefficient of friction of a grass turf by sliding a mass down it and using an energy lens. I think your drawings could have been more exact, but you got all the parts there. IMPORTANT… Sebastian didn’t declare a lens! What was the lens he used to find the normal force? Lastly, you say that you are calculating the final speed, but you use the formula for average speed. It would have been good to explain that this was the average speed for that last section of track, so it is the speed in the middle of this section. The final speed must have been just a little bit higher, which would have slightly lowered your calculation for coefficient of friction. In general, I found this well done. #10 Projectile Motion of a Marble: Megan Arnold, James Burwell, Ian Henderson, Richard Nguyen. We will analyze the energy transformations and kinematics of a marble launched from a spring. I found this to be really well done! You consistently change between energy and kinematics lenses, identifying each, and using each correctly. You several times say the wrong units or direction. You also mention the “kinetic energy vector”… of which there is none… I think you meant to say, “the kinetic energy associated with the vertical velocity. You also solve the problem in a very odd manner going step by step with energy and kinematics. It took longer than is necessary. However, as I stated above, I really like how you did this. This was way longer than 5 minutes, but you already know that. It might have been a good idea to speed up some more of the writing and drop out the pauses… but I can tell you that this would take lots of time to do! # 0:27 seconds ## What type of energy do we start out with right before the ball is shot? ### Potential Energy of the Spring (correct) ### Kinetic Energy ### Gravitational Potential Energy (correct) # 2:40 ## If the velocity of the bullet is 6.1 m/s, what’s its Kinetic Energy? ### 10 J ### .5 J ### 2 J ### .1 J (correct) # 3:27 ## What is the spring constant? ### 108.2 N/m (correct) ### 115 N/m ### 50 N/m ### 105 N/m # 6:20 ## What stays constant throughout the trajectory? ### Mass (correct) ### the bullet’s vertical velocity ### Kinetic Energy ### the bullet’s horizontal velocity (correct) #11 Energy of Bowling Ball: Joey Salvucci, Kathryn Webb, Angel de la Torre. We will analyze how much force is put onto a bowling ball using the energy lens, the bowling alley speedometer, and the tracker software.Bowling Energy Lens #12 Collisions between Billiard Balls: Matt Bryan, Adam Gonzalez, Jack McGee. We will investigate the different types of collisions between Billiard balls. Collisions in Pool This is our new video. I wonder why your video is so tiny. It is hard to read what you write. Your 5 J elastic collision example has several mistakes in it: is there really 5 joules of kinetic energy in the ball when it is on the ground? How about when it is back in where you dropped it again? Similarly, when your ice cream falls out of your cone, would it start with 5 joules of kinetic energy? You many times state that the initial and final momenta are the same, but don’t explain it. How is it that when the ball is going up, the momentum is the same as when it’s going down is the same as when it starts is the same as when it changes direction on the ground? It seems you didn’t do anything quantitative either, there’s no numbers or calculations. As it is, your video satisfies only 2 of the rubric’s criteria and thus receives a “C”. If you want to do better, please submit another video. After reading this, the group made another video. My new response was: Your new video is of much better quality and is more quantitative. However, there are two places where if fell short of being spectacular: You could have checked the final velocity of each ball to see if your calculations were correct. You could also have checked kinetic energy to see if the collision was in fact elastic. If you would have done either of these, your calculated velocity was way too low. Why? Because momentum is a vector – and for this problem, you really needed to do a vector diagram to show you were adding the momenta.. Your final velocity of 1.84 m/s is just the x component of the final velocities of each ball. When you consider that they went off at about a 45 degree angle, you would find that the absolute final speeds were root 2 times 1.84 m/s. In doing the kinetic energy calculation, you could then show that kinetic energy is roughly conserved, and you should also find from calculating the final speeds of the balls, that you are close to correct. I think it’d be great if you did this. However, your video is fine as is for achieving a good grade. #13 Mountain bike spring: Brooks McCann, Luke Surmeian, Adam Bloomer, Jose Cruz. We will be calculating the K value of a spring on a bike. I think you made one large mistake. Not all your energy is absorbed by the FRONT shock. Isn’t this the case? Please make this consideration and write it up and submit it to me with a correction. Thanks #14 NERF Gun Projection – Jordan, Leo, Kennedy, Emily Velocity, projectiles, and distances. Straight up kinematics, and some energy. We will be firing a nerf gun at a wall: variables include distance from the wall, angle of gun, and mass of projectile. Then figure out the physics behind it all. You really shouldn’t carry calculations out to 4 significant figures when you take measurements for them to an accuracy of only 1 or 2 significant figures. This implies that you know the accuracy much more than you really do – and much more than you’d even care to know them. But OK, the video was fine. 1:12 What function should be used to find the angle at which the the bullet is shot from the gun? Conjuction Junction whats your function F=m*a e=m*c^2 tan^-1(rise/run) (correct) 1:32 Why is it good that it is a narrow spread of bullet marks? angle is consistent velocity is consistent bullet is the same weight its the same distance each time All of the above (correct) 2:25 What lens should you look through for this problem? Kinematics (correct) Dynamics Energy Momentum 3:06 What is the first step to solving for the problem? F=m*a Find the components of the velocities find the equations (correct) Find the time 4:35 What would happen if we added a weight to the bullet? It would have more energy It would not make a difference for kinematics It would change the height at which it hits the board (correct) #15) Marissa Dierkes, Kevin Church, and Owen Staveland link: In Educanon with questions Questions: 1. @ 36 seconds “What lens would be best to use to find the coefficient of friction” a. mechanics b. dynamics c. energy d. kinematics answer: b 2. @ 1:01 “What are we forgetting to mention here? Choose all that apply” a. the direction of acceleration b. nothing, you guys are fine c. the direction of the positive x and y axes answer: a and c 3. @ 1:23 “Why is the vector sum of the forces in the y-direction equal to zero” a. Because the force of gravity and normal force is a newton pair b. the block is not accelerating in that direction c. its always 0 answer: b 4. @ 1:57 “Are we still looking through the dynamics lens? a. yes b. no, this is kinematics c, no, this is momentum d. no, this is energy answer: b 5. @ 3:53 “Wait, doesn’t the coefficient of friction have to be less than 1? Choose all that apply” a. no, everything’s good here b. yes, in perfect world physics c. these kids are dumb and wrong d. this is caused by other factors such as air resistance and sound You made a few mistakes in the video, but I like the video. I’ll likely use it for the class. I hope you’re good with my pointing out the mistakes… right? Below this line are videos from Winter, 2015**__ #2 Spinning in hammock: Ben Lakes, Brock Armstrong, Tasha Haddod, and Will T. We will calculate the centripetal acceleration of Ben spinning in a hammock. This is a Kinematics and Dynamics problem. This video achieved the objectives. There’s a problem with your conclusion… you have arrived at an acceleration for Ben to be close to twice that of gravity. If this was the case, the hammock would be pulling him downward with close to the force of gravity, but we can see that the hammock is almost slack when he is at the top? How could this be? You calculated the average omega by dividing 2*pi by the time it took to go all the way around. However, at the top you were going much slower than at the bottom (lenses: energy or dynamics). You could have used tracker to find the speed (or omega) at the top, and I’m sure you’d find it is considerably slower than your average speed. 1:37 : Another way of saying 1.44/s is 1.44 2pi/s 1.44 seconds (correct) 1.44 radians per second This is the only way to say it. 3:21 : Which lenses do we use? (correct) Dynamics Energy (correct) Kinematics Momentum 1:55 : What does w stand for? Ben’s weight The arc length of his rotation (correct) Angular velocity (correct) Omega 2:45 : What is centripetal acceleration? (correct) The acceleration inwards along the radius vector of the circular motion The acceleration that Ben’s body is moving towards the hammock The acceleration that Ben’s body would move out of its path is there is no more tension from the hammock 4:16 : Why didn’t they calculate the sum of the forces? They’re lazy! They didn’t want to go over time! (correct) They do not have enough information #3 Firing a catapult: Matthew Whitman, Corey Harris, Mason. We will look at how a catapult turns potential energy into kinetic energy, and then examine the resulting launch using kinematics. This is an energy and kinematics problem. Examine the Launch of a Catapult, This video achieved most objectives. The problem is well done, but only somewhat unique from what we’ve done in class. #4 The Forces of Hiking: Megan Haines, Maddi Fleming. We will explore the coefficient of friction and how that affects hiking or falling down a hill. This video achieved the objectives. Possible Educannon questions: 1) What direction is the acceleration? (When we talk about the sum of forces and direction of acceleration) upward downward to the left to the right down the hill to the right 2) What force is used to calculate the normal force ( when we set up our initial components of forces equations) the full force of gravity the perpendicular component the parallel component 3)Will you hike in cowboy from now on? ( at the end :)) yes, because I like to fall no, because I like to stay on my feet Project #03905 Power necessary to bike and run up Cerro hill: Sara Baldridge, Emily Neal, and Jose Ramirez. We will explore the physics behind Cerro residents daily trek including physics physics and more physics. Dynamics, Kinematics, and energy; why not. #5 Riding a bicycle versus riding a unicycle: Lydia Hedge, Luis Curiel, Luis Wiley, Sarah Morlan, Samantha Galicinao, Mira Brown. We will film two separate videos. The first to look at the difference in energy needed to ride a unicycle versus a bicycle, this is an energy problem. The second video will look at the difference in kinematics between a unicycle and a bicycle, this is a kinematics problem. Links to Videos: Walking vs. Biking Part I: Walking vs. Biking Part II: These videos achieved some of the objectives, but have one important mistake in them, and a few minor mistakes. Both mistakes relate to understanding that power is the rate of change of energy. So if you have a 100 W light bulb, for instance, it puts out 100 Joules in one second. If you wait a minute, then you will have 6000J, but the rate of power output will still be 100 W. For your final power output, I think that you multiplied the power for one meter by the total number of meters (but I’m not sure) and got unrealistic power putouts. The total power output will likely be the same as the power output for one meter. I human is not capable of putting out several thousand watts. The other mistake has to do with kinetic energy. You only gain kinetic energy in the beginning when you are speeding up. After that, the speed seems to be constant so that when you subsequently calculate the power (which is change in energy divided by change in time) there is no change in kinetic energy, so the kinetic energy would not enter into the power – only the change in potential energy because your potential energy is still changing. #6 Velocity with two Ballistics Pendulums: Laura Mountain-Tuller, Alyssa Briones, Tessa Gunnin, Bella Harbert, Kyle Branch, Sidney Collin, Christine Truong. We will make 1 video, with two projects within it. In each project we will try to calculate the velocity of a BB using two different Ballistics Pendulums. We will use kinetic energy, potential energy and momentum to track this. Your second ballistics speed measuring device is amazing. People have used this technique to measure speeds of subatomic particles – I used it in college to measure speeds of neutrons coming from a reactor. Your initial pendulum measurement seems wrong to me. The rise in height was 25 cm? or was it 2.5 mm? Did you notice you hit the clay off center, so there is a wonderful opportunity to do a angular momentum analysis. In any case, it doesn’t make sense to me. I do not get 1.04 m/s regardless of how I interpret this. Please clarify to me. 1. What lenses are theses problems? a)momentum b)energy c)rotational kinematics d)all of the above 2. What relates the angular velocity of the wheels to the linear velocity of the bullet? a)tacos b)time c)momentum d)energy #7: Forces involved with (hopefully) bowling a strike: Hannah Chou, Carrie Simmons, Ciara Helland, Colin Empey. We will each attempt to bowl a strike, and, whichever pins we hit down, we will calculate the direction of the force the bowling ball inputs on the pins in order to show why those (or all) the pins fell and why others may be left standing. This video achieved the objectives. Ciara could also relate the rotational to the translational motion. You found average omega… final omega might be about twice that? Or final omega might be the speed of the ball (as measured by the lane device) divided by her arm length. Are they about the same? Then the acceleration of the ball should be the angular acceleration of the ball divided by her arm length. You can find the angular acceleration by d(omega)/dt. #8: Energy in a trampoline bounce: Katelyn Ingwerson, Robbie Hou, Dagur Gudmundsson, and Riley Harden. We will make a video showing a person jumping on a trampoline, and we will measure the energy in the system, and the changes it goes through. This is an energy problem. Here’s our video: There were several mistakes in this video. I think. I don’t know where you got your values from (how the measurements were taken), so it’s hard to tell exactly where the difficulty/discrepancy happened. Please talk to me if you’d like to correct this. #9 Forces in rock climbing with ropes: Ben Van Hamersveld, Angie Larson, Tyler Hall. We will calculate how friction allows the belayer to easily hold a person on the rope, even if the climber is heavier than the belayer. We will find all the other forces including the elasticity of the rope and record the mass of the people involved. Where does the capstan equation come from? The video was fine and achieved the goals. #10 Energy in a slingshot: Joe DeCesaro, Ace Elliott, Jordan and Krystal. We will find the elasticity of a spring and how far we need to stretch it in order to make a basket. Video is OK. The treatment of spring constant is either incorrect or I don’t understand it correctly, because you are not stretching it to shoot the ball the same way you measured the spring constant. In fact, the way you stretched it in a triangle, I don’t think it acts too much like a linear spring. Did your measurement of the height agree with what you calculated? 1. What lens should we look at? (1:30) a. Dynamics b. Energy c. Momentum d. Kinematics 2. What will be the initial energy? Check all that apply (1:42) a. Gravitational potential energy b. Elastic potential energy c. Kinetic energy d. Work e. Potatoes 3. Why can’t you use work to solve this problem? a. We can use work b. The force isn’t applied for the entire distance c. We don’t know the distance d. We don’t know the force 4. How do you calculate the spring constant? (2:41) a. Look it up in a book b. Measure the distance stretched using a known mass c. Stretch the spring as far as you can 5. What did Joe forget to consider? (3:51) a. Nothing, he is perfect b. We stretched the spring from the middle c. The distance should be split in half d. The distance should be doubled so we can launch it further 6. Joe accidentally put an 8 at the end of the answer. What should happen to Joe? a. Nothing, it’s chill b. Burn in hell!!! #11 Dropping a spinning disk that is attached to a rod with two strings: Michael Fekadu, Kade Huber, John Griffin, Garret Taylor. We will talk about angular momentum and torque. Enjoy the video 🙂 The video was well done. I would like to see some analysis – what is the height it fell? what was the omega at the bottom? How should these be related and are the measurements consistent with what you calculate? There is an oversight in the calculation of intertia: the mass of the spindle is not the same as the mass of the wheel, so you should differentiate. However really you should just argue that the inertia of the spindle is negligible – and support it with a quick calculation. The torque = rate of change of angular momentum is OK, but I think that this is much better to use an energy lens – you’re not really conserving angular momentum because of the outside torques of the string and gravity, but you are conserving mechanical energy (minus what is lost to friction over time). #12 Calculating the Frictional Coefficient of a 2015 Acura NSX Concept (fractional scale) on four different kinds of surfaces. Sara Baldridge, Emily Neal, Jose Ramirez. We used the Dynamics lens. Video is good. You could have used an energy lens and just measured the distance the car goes. That would have been easier to me. The kinetic energy the car has at the beginning is equal to the original potential energy of the car on the top of the ramp is equal to the work done by friction to bring the car to a stop. Anyway, thanks. Le Youtube