Conservation of Energy - Testing Physics

Expanding on the previous session, we test the concept of conservation of energy for systems involving kinetic energy, gravitational energy, and spring energy. We also test the properties of elastic collisions and show that both the total momentum and total kinetic energy are conserved.

0:00 Introduction
0:37 Calculating Gravitational Potential Energy
8:38 Testing Energy Conservation with Gravitational Energy
12:13 Calculating Spring Potential Energy
19:59 Testing Energy Conservation with Spring Energy
25:03 Calculating Energy and Momentum in Elastic Collisions
32:37 Testing Energy & Momentum conservation in Elastic Collisions
42:08 Testing Springs Launching Carts and Energy Conservation

Here's some of the velocity data (approximate based on readings of graphs) if you want to check the numbers:
Elastic Collision #1: m1 = 0.558kg, m2 = 0.303kg, v1i = 0.45m/s, v2i = 0m/s, v1f = 0.14m/s, v2f = 0.56m/s
Elastic Collision #2: m1 = 0.558kg, m2 = 0.303kg, v1i = 0.37m/s, v2i = 0m/s, v1f = 0.11m/s, v2f = 0.47m/s
Elastic Collision #3 (redo) : m1 = 0.309kg, m2 = 0.676kg, v1i = 0.63m/s, v2i = 0m/s, v1f = -0.21m/s, v2f = 0.38m/s
Inelastic (stick together) Collision: m1 = 0.309kg, m2 = 0.676kg, v1i = 0.53m/s, v2i = 0m/s, v1f = 0.17m/s, v2f = 0.17m/s
Elastic Collision #4 (thrown at each other) : m1 = 0.309kg, m2 = 0.801kg, v1i = 0.36m/s, v2i = -0.25m/s, v1f = -0.49m/s, v2f = 0.094m/s

Low masses spring launch: m1 = 0.294kg, m2 = 0.293kg, initial velocities are zero, v1f = 0.53m/s, v2f = -0.54m/s
High masses spring launch: m1 = 0.792kg, m2 = 0.790kg, initial velocities are zero, v1f = 0.33m/s, v2f = -0.33m/s
Different masses spring launch: m1 = 0.294kg, m2 = 0.790kg, initial velocities are zero, v1f = 0.65m/s, v2f = -0.25m/s

[_John_Sean_Walker]

Beautiful, Michael.
Nice to see the magnetic potential.
Thanks. 👍

[WhiteHenny]

A great case study in the importance of units.

In today's DraftScience video, "Live 6-13-23 ... re: PhysicistMichael will not argue the argument", right at the end (1:36:52) they are talking about an experiment where a 1 mass with 100 velocity hits a 2 mass that is at rest. If the collision is elastic, conservation of momentum and energy tells us that the 2 mass will gain 133 momentum while the 1 mass will rebound with 33 momentum.

A commenter was trying to explain that the 2 mass only gets 66 velocity, while Gary gets increasingly irate and ends up hitting his whiteboard and banning the commenter while shouting "the small mass will go 33 this way. the big mass will go 133 forward. there's no doubt about the 133 forward".

If he took the time to say "133 units of momentum" or "133 units of velocity" the misunderstanding could have been avoided.

In general taking care to always mention the units helps clarify the thinking. "It goes 133" is quite ambiguous.

[pyrrho]

@physicistMichael I want to say I think these videos are great and I also agree that gary's confusion/arguments do drive into just how interesting and confusing "classical" physics is. It's something people should understand more, especially the reductionism of everything to distance, time and mass, the strength of physics, and also its weakness, i.e. with things that so far can't be reduced to those metrics (like emotions, so far :). I just want to help you understand. Understanding the errors Gary is making in the name of "common sense" is in fact worthwhile, b/c they actually are things people could understand better, even people that already believe them, even people that already understand them. Sometimes things I hadn't thought too much about, like the interesting symmetry of Work being Fd and Momentum being Ft.

One thing I agree with Gary on is there ought to be more of these type of experiments on youtube, though he's silly to expect everything to be a video on youtube or it's never happened. Thanks for the videos and I personally think a good outcome would be a robust conversation about these issues with a hands on aspect like you are taking. Cheers.

[pyrrho]

Other Subject: for a while I thought about getting a track and sensors and doing these kinds of experiments, not to convince Inmendham which I think is impossible, but for the reasons you are doing it... it's interesting and there is a lot to learn from it for viewers, it's a good service. But the tracks for sale are not only expensive but all proprietary. I wish there was an open source option, but I didn't find one, something with arduino sensors and non-proprietary software, and while the tracks are maybe fairly priced based on their precision construction, the sensors are out of whack with the current plethora of cheap sensors. I've looked a little at getting someone to produce an open source alternative but at this point that's a post-retirement project for me :)