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Re: positive and negative work



Brian Whatcott wrote:

We use Professor Leigh's favorite model: the car rolling on an incline.
Let us suppose that Michael is sitting in this car, which has started to roll
backwards, downhill. He wants to proceed slowly astern, so he applies a little
throttle while he is in a forward gear. This prevents the car from
careering away.

The work done by the car, we say, is negative. There is no discussion,
no debate.
This is the convention.

I disagree. The car exerts a force on the road surface, which is
stationary, and the tire is rolling so the frictional force is static, not
kinetic. It seem to me that the car is not doing any work on the road
surface. Is there anything else the car is doing work on?

Gene

--
Eugene P. Mosca
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