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Re: Car acceleration



In regard to a disk rolling down an incline withoput slipping

On Tue, 5 Feb 2002, Robert Carlson wrote:

As a second thought, I would consider static friction to be a
nonconservative force in mechanics. Do you agree?

Yes.

If so, then if it does work

Not "real work", pseudowork.

of the negative gender (is this male or female?)

I'm not touching that one. ;-)

then the total mechanical energy should decrease.

No. First of all pseudowork only changes the bulk translational
kinetic energy. Second of all, in the case of a disk rolling down
an incline, friction is not the only force doing pseudowork;
gravity also does pseudowork. The total pseudowork is positive
and equal (as it ALWAYS is) to the change in the bulk
translational kinetic energy.

Gravity is the *only* force that does "real work" in this case and
the work it does is equal to the change in the *total* kinetic
energy of the disk. Another way of saying the same thing is to
say that no nonconservative work is done on the disk and therefore
its total mechanical energy (total kinetic plus gravitational
potential) is unchanged.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm