# 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. https://drive.google.com/open?id=1diuO7s_u3tOzuSGUd52OauZCG_cp2oje. 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: https://youtu.be/8OQS5A-z2Vc
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”.: https://www.youtube.com/watch?v=TcP1saVpNOg&t=12s  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.  https://www.youtube.com/watch?v=QkDtazlqHEI&feature=youtu.be 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: https://youtu.be/aIGXZ_fuKx0 (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 https://youtu.be/P7465sNC1Ig 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. https://www.youtube.com/watch?v=uMDFW4p3H24.
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? https://www.youtube.com/watch?v=LePU2IL9Wb8. 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: https://m.youtube.com/watch?v=pRVQVEEFLuoI 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. https://www.youtube.com/watch?v=SYuALhyHnic&feature=youtu.be  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. https://youtu.be/tkBW7MPoAdU 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. https://www.youtube.com/watch?v=_aZto-3502A
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: https://youtu.be/WNaQk6D4upoThis 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. https://youtu.be/AhkhUhLiqp4.
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.
https://youtu.be/iHaK-PSSY74 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.
https://youtu.be/OTTIP7jDzq0
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
https://youtu.be/fqnFEL8clSg
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
https://youtu.be/6k1KhNrvOLg
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!
https://youtu.be/zbYOGcDkPzk
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
Watch: RACE! note: HIGHER QUALITY VIDEO UPLOADED
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.
Question
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.
https://vimeo.com/272896495
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.
https://youtu.be/w3eJbC-9I9E
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
Questions:
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”.
Questions:
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?
https://youtu.be/LPfxpe9Q77o
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!
https://youtu.be/xE2I-qCvhtM

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.

https://youtu.be/jSW7WvBpt7s
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.
https://youtu.be/U_QB2sYh8xM
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.
https://youtu.be/J3Bj51n1__Y
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.
https://youtu.be/mIWW6eAj7Sg
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.
https://youtu.be/608g_EkovbU
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.
https://youtu.be/iVkfhOl2EMU 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.
https://youtu.be/qyurLGzfo5U
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.
https://youtu.be/7V0PxA7Yf7g
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.
https://youtu.be/BVT8_2z4ko8

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.
https://youtu.be/Jf7E1dbNXT4
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.
https://www.wevideo.com/view/933061283
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
https://youtu.be/RAgAI1EHy2g
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:

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.
https://youtu.be/IZhF7UxNF8E
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.
https://youtu.be/8vqjfD1xRzI
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:
https://youtu.be/IEleH2CUees

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.

UPDATED VIDEO:

#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. https://youtu.be/6oVvfEYnPeY
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. https://youtu.be/U3Y6_vrYcGQ
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).
https://youtu.be/BiV8-mvLKI0

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. https://youtu.be/vmwVh2xv_No [ ADDENDUM: https://youtu.be/FvPCQl6UUzI ]
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. https://youtu.be/vLqURao0nCk
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. https://youtu.be/-NUR_ObEkhA
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. https://youtu.be/0dQBxgJlGYg 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:
https://youtu.be/Nj8U3B6-O3k
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 https://youtu.be/r7LfHuACaKc
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.