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Re: ENERGY WITH Q

-----Original Message-----
From: John S. Denker [mailto:jsd@MONMOUTH.COM]
Sent: Tuesday, October 30, 2001 8:29 AM
To: PHYS-L@lists.nau.edu
Subject: Re: ENERGY WITH Q




I whack the end of the plunger with a hammer. There is a large force
applied over a nonzero distance. I calculate F dot ds in the
only way that
makes sense, namely the force (at the place where the force
is applied) and
the distance (at the place where the force is applied).

Why doesn't it make sense to calculate the dot product of the applied
external force with the displacement of the center of mass of your
contraption?


It is simply not true that calculating F dot ds tells me the
increase in
the kinetic energy of this object. Some of the energy goes into
compressing the spring.


But is it true that F dot ds_cm is Delta KE? Which I think is the claim
Carl is making.