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# Circular motion help watch

1. Hi, so, I needed explanations for vertical circular motion, so I searched for it and found a site with pretty decent explanations for it.

http://seanelvidge.com/2013/02/veloc...loop-the-loop/

If you'd take some moments to read it, then you'll understand my doubts.

I don't understand why the potential energy at the bottom is 0, whereas at the top, kinetic energy is not 0?

I've always learnt that an object is always momentarily stationary at the maximum point of a parabolic path, so why not here? Shouldn't K.E = 0?
2. (Original post by fandom-queen)
Hi, so, I needed explanations for vertical circular motion, so I searched for it and found a site with pretty decent explanations for it.

http://seanelvidge.com/2013/02/veloc...loop-the-loop/

If you'd take some moments to read it, then you'll understand my doubts.

I don't understand why the potential energy at the bottom is 0, whereas at the top, kinetic energy is not 0?

I've always learnt that an object is always momentarily stationary at the maximum point of a parabolic path, so why not here? Shouldn't K.E = 0?
Well it's looking for the *minimum* speed at which the rollercoaster riders buttocks have no contact force against the seat... and that speed is greater than zero.- so KE is greater than zero.

the riders buttocks would also have no contact force if the speed at the top of the loop was zero but that's not what the guy was looking for... and the ride coming to a permanent halt half way round is something the designers will usually try and avoid.

BTW at the top of a parabolic path it's the vertical velocity which is zero - it's still got a non zero component of horizontal velocity so the KE isn't zero there either.
3. (Original post by Joinedup)
Well it's looking for the *minimum* speed at which the rollercoaster riders buttocks have no contact force against the seat... and that speed is greater than zero.- so KE is greater than zero.

the riders buttocks would also have no contact force if the speed at the top of the loop was zero but that's not what the guy was looking for... and the ride coming to a permanent halt half way round is something the designers will usually try and avoid.

BTW at the top of a parabolic path it's the vertical velocity which is zero - it's still got a non zero component of horizontal velocity so the KE isn't zero there either.
Aah, thanks! I completely forgot about the horizontal component.

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