Loop de Loop

Posted by: Hubbell to Sciences » AP Physics » Videos » Centripital Motion and Universal Gravitation

Reid Dickerson works a Uniform Circular Motion problem that also requires knowledge of energy conservation.

Score: 53

Elena Escalas says: I thought it was very helpful that he decided to use a harder problem and incorporate different concepts into his work. If I were to do this problem, I think the key that I would miss, that I thought he explained quite nicely, would be the fact that the centripital acceleration at the top of the "Loop de Loop" is equal to baby g. Also, the Dr. Fitz inside of me must point out how he "divides out" the mass and baby g from his equations at the end. The lovely and surprisingly nice result at the end almost seems too good to be true. I wonder if his findings translate nicely to dealing with other instances where there is a "Loop de Loop," or if his nice answer is only special to this case. It seems like the answer would translate nicely, because most things "divide out" so nicely when he deals with energy.

Jessie Baskauf says: Elena makes a good point about the nice answer. I think the answer would often work out fairly nicely, because in any "loop de loop" problem you should be able to view it from the perspective of the object at the top of the loop, and thus the centripetal acceleration should always be able to be written in terms of baby g only. After that, everything with energy just depends on where you start and where you finish, and viewing things in terms of energy tends to make everything nice and simple in the end. I do think the result would be different if there were friction, though, but then it seems like the problem would be much more complicated since the force of friction would change as the object went around the loop and its angle relative to the ground changed, therefore changing the normal force.

Maggie Kidd says: I really enjoyed this video. Honestly, this problem would be one that I would have trouble with if I tried to do it on my own. Reid worked it out slowly and efficiently and I really liked the simplicity of the video and how it worked out in the end. I kind of wish there were some jokes included though, because Reid is a hilarious person.

Hannah Aaron says: I thought this video was very well done. As Elena pointed out, the key to the problem was discovering when the centripetal acceleration equals gravity. Reid explained it in a very understandable way that made a lot of sense to me. As others have mentioned, I too enjoyed seeing the answer turn out so nicely. It fascinating me that the mass of the cart does not actually matter, because I never would have guessed. Kudos to him for making a tough problem seem easy.

Kiana Jansen says: the way that this problem is explained made it very easy to follow. i realized that i would have probably messed up in knowing that the top of the loop was baby g as well as the simple mistake of adding the value that was initially determined to the value of the loop itself. but overall the problem was very well explained.

Dev says: Thanks Reid!! The video really helped me with grasping some of the ideas of Uniform circular motion (something that I myself have been struggling a bit with). Not only that, but incorporating the uniform circular motion and kinetic energy into one problem is a double plus in my book because I might have some trouble with this myself. The solution is also super nice as mentioned before.

Will Mason Moses says: Nice video

Nora Gilligan says: I thought this was a good video. I liked how he combined two major topics in one problem that we had never seen before. It was a little weird how the h on the diagram was different to the h in the equations but he clarified that later. He did a good job explaining everything in a simple way so that anyone could understand what he was doing.

Youssef Doss says: I thought this video had a couple of minor moments that really helped in the execution of this problem. First, there was the realization that at the top of the loop, acceleration equals baby g, as there is no centripetal force acting on the cart at the top of the loop. This would have been really easy to miss, so it's nice to have that explained so explicitly. Also, not solving for v squared made it so that instead of just solving this problem, he solved all problems of this type. I feel like a lot of AP Physics students (myself included) wouldn't have thought to do that.