- #1

Sam McCrea

I'm confused about velocity in a "loop the loop" situation. Say (theoretically) a car was going minimum speed around a loop (which I understand is sqrt of rg). Therefore the total energy must be the kinetic energy that allowed it to go that minimum speed at that point plus the gravitational potential energy. This therefore must be all the kinetic energy the car has at the bottom of the loop and if you rearrange this to find the velocity is a different value from the top speed. This must mean the velocity is getting smaller as it goes up the loop as energy is being changed however this must mean it is not uniform circular motion and centripetal force is not constant.

However on a ball attached to a string in vertical circular motion I read that as the ball nears the bottom of the loop the tension force increases which balances out the gravity force component making the centripetal force constant and from looking at the formula this must mean the speed is constant (velocity is the same value but constantly changing direction). However I read on another forum that it would still not be uniform circular motion and would be constantly changing speed (https://physics.stackexchange.com/q...form-circular-motion-can-it-really-be-uniform) but I do not understand the explanation. From this site here (http://www.schoolphysics.co.uk/age1...n/text/Motion_in_a_vertical_circle/index.html) tension is calculated from only one velocity value.

As you can see I'm quite confused so can someone please tell me where I'm going wrong.

Thanks