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Re: [Phys-L] friction



Yes, I think you may have missed something. The point of application of the force is at the sole of your shoe. The shoe (hopefully) does not slip relative to the ground. Hence there is no work done *at the point of application of the force*.

What you are talking about instead is the force down at the shoe multiplied by the displacement of your center of mass which is far away from the shoe. That’s pseudowork. It’s not “false” but it’s not work as in what enters into the first law of thermodynamics.

On Sep 26, 2017, at 1:03 PM, Richard Heckathorn <geepaw@wowway.com> wrote:

From my perspective, when I walk, I push on the floor and the floor pushes back on me. As this force pushes on me through a distance, work is done on me.

A previous statement said friction pushes on me. Again from my perspective this is not true.

Now have I missed something?

Dick

Have a Great Day

Website rheckathorn.weebly.com



On Sep 26, 2017, at 9:32 AM, brian whatcott <betwys1@sbcglobal.net> wrote:


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?

--

A living thing is too subtle to make a just target for a teacher's homily.
How much simpler to cite a steam locomotive, whose energy is in the burning of wood or coal acting on water whose steam forces wheels to turn if it can, and which it does when too much effort is expended in moving a thousand tons of train into motion, and where drive wheels shed streams of sparks on the rails beneath, until the steam is turned down to a value less than the critical value of wheel-rail friction, when the train moves serially into motion, with plenty of sound and fury from the percussion department of couplers.

Brian W
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