Energy of Rolling on a Hill

 Rolling with friction

 This simulation shows a ball rolling down a hill while the force of friction acts on the ball.  Notice that the GPE it starts with ends up being converted to KE and finally ends up all as internal energy (heat).

There is a very common misconception that gravity causes objects to come to rest. This is FALSE. It is very important to realize the TRUTH. The TRUTH is that friction causes the ball to eventually stop, not gravity.


 Rolling without friction (sliding)

 This simulation shows the same ball rolling (sliding really) down the same hill but this time friction has been removed. Notice that the ball slides up to an equal height on the other side of the hill. This sliding would continue, back and forth, forever.....or until some net force acts on the ball.  The same height also tells you that the GPE is the same on each side of the hill.  Whatever energy it starts with at the top is the same it ends with.  Since no energy is lost due to heat (through friction) the ball always maintains the same energy it started with.

Notice that in the absence of friction, there is no torque placed on the ball to cause it to rotate. Friction is responsible for rolling as opposed to sliding.

This simulation assumes there is no friction of any kind.

1998 Science Joy Wagon