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Re: Conservation of ME and nonconservative forces

Friction does no work in this case because there is no slipping. That is,
there is a force but no displacement of the contact point.

The problem is easily done using torques and Newton's Laws and the same
answer is achieved.
Oren Quist, SDSU

-----Original Message-----
From: lorinda.stinnett [mailto:stinn001@BAMA.UA.EDU]
Sent: Tuesday, June 26, 2001 3:56 PM
Subject: Conservation of ME and nonconservative forces


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

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
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.

Lorinda Stinnett