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Re: Car acceleration



On Tue, 5 Feb 2002, Robert Carlson wrote:

In a message dated 2/5/2002 9:44:41 PM Central Standard Time,
ajmallinckro@CSUPOMONA.EDU writes:
...
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.

It seems to me you are complicating things again. Why not say that static
friction does no real work and the only force doing real work is weight?
Then, since weight is a conservative force, energy is conserved. This is a
much simpler explanation and is verified by experiment. Why complicate
things with not real work?

I thought that was *exactly* what I said (except that I prefer
"force of gravity" to "weight".)

IMO, pseudowork is not a particularly useful entity in the
analysis of a disk rolling down an incline. I only mentioned it
earlier because you wanted to know how my views on the
accelerating car (where pseudowork is *very* useful) could be
reconciled with what happens in the case of the disk. I explained
to you how it can be reconciled; I didn't claim it was useful or
even enlightening (although I think it *is* that) to do so.

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