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Re: [Phys-L] friction



Pseudowork.

Sure enough, the road does not transmit any energy to us. The kinetic energy I gain when I start walking comes from my internal chemical energy. It is not transmitted by work across the boundary from the road to me.

Incidentally, kinetic friction is also not work alone. Some of the sliding results in warming up the book and not just the ground, so not all the work is transmitted across the boundary from the book to the ground. This happens because friction does not occur at a single point of application between the book and the ground. Little asperities both on the bottom of the book and on the top surface of the ground get set into wagging motion.

There are lots of articles that explain all this stuff. Start with articles and the Matter & Interactions textbook by Bruce Sherwood for instance.

On Sep 25, 2017, at 3:31 PM, Anthony Lapinski <alapinski@pds.org> wrote:

Kinetic friction does negative work on a sliding book, which makes it stop.
And static friction moves us forward when we walk. But there is no
slipping, so static friction does no work on us. Yet we move forward. How
can this be explained to kids in terms of work and energy?

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