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Conservation of ME and nonconservative forces



Hello,

I am teaching the first semester of the introductory calc based Physics -
first time.

I am in need of a good freshman level explanation to the following
problem:

A ball rolls down an inclined plane without slipping. Given the height
from which it starts, find the speed of the ball at the bottom of the incline.
So we look at conservation of ME.

But in order to use cons. of ME, we need to be certain that there is no
work done by nonconservative forces.

Forces on ball:
1. Gravity - conservative - OK
2. Normal - does no work on object - perpendicular to direction of motion
- OK
3. Static friction at the point of contact between ball and surface. ??

I am believe I understand that the static friction does no work, I am
looking for an explanation my students would understand.

Thanks,
Lorinda Stinnett