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Re: [Phys-L] friction



I use the analysis of a ball rolling without slipping down an incline for a problem that can be precisely analyzed. In that case, static friction also does no work, but it’s plausible to claim that static friction “mediates" a conversion of gravitational potential energy to rotational kinetic energy.

In the case of walking, if you do not adhere to notions of pseudo-work that I’ve seen reference to, then the force of static friction does no work but mediates the direct conversion of internal chemical energy to kinetic energy. Of course, if you go deep enough, the conversion of "internal chemical energy” can be viewed as microscopic F dot dx work again, so I would say it depends on how far you want to take it.

I’d be happy to see other discussions of this; maybe I can benefit from an even better approach to an explanation.


Stefan Jeglinski


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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