Re: pinhole Hewitt and circular motion

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Fri Dec 10 1999 - 14:02:14 PST 

Message-Id: <l03110716b47728185f64@[192.174.2.173]>
Date: Fri, 10 Dec 1999 14:02:14 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Hewitt and circular motion

Hi Mark
Good question again.

The exact definition of work is the intergral of the product of the force
times the component of the distance moved parallel to the force.

At every infinitesimal instant the force and the distance moved are
perpendicular so the work done by gravity to keep the moon in a perfectly
circular orbit would be zero. (You have to do the integral instant by
instant that's why you can't wait a quarter of an orbit and say "see it
moved in the direction of the force.")

Indeed no work is done.

yet it moves.

Paul D

Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld

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