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Re: ENERGY WITH Q



Hi Fellow Philosophers of Science,

I have now consumed about 48 to 100 hours on this (I was going to say
non-problem) -- problem, which is a pretty nasty one considering its
simplicity. I feel somewhat entitled to an explanation of pseudowork
because my computer was down at the time it entered the thread. I have
a serious suspicion that a lot of physicists are calling
something-that-can't-raise-a-weight Work, things that serve as vectors
(in the biological sense) for entropy, and other strange and weird black
magic. I really find it hard to talk about work being done on a
no-see-um among other incoherent no-see-ums, and, yet I have had no
compunction about arguing with Dave B. about work done by photons upon
other photons and such like no-see-ums.

I expect an answer from Jim, but anyone may comply. *We* will remain
amused. :-) (Maybe because I don't have to ever go back into another
classroom. I have been offered an opportunity to lecture (on my
subject, which I guess used to be the application of topological
principles to numerical methods to solve the nonlinear equations
associated with separation processes) at various universities in India,
but everyone I know who goes to India dies, so I won't go.)

Regards / T
----- Original Message -----
From: "Jim Green" <JMGreen@SISNA.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, November 28, 2001 1:35 PM
Subject: Re: ENERGY WITH Q



A block slides to rest along a level rough table. The only net force
on the block is kinetic friction. The table is clamped to the floor
and hence to the earth. We approximate the earth as being an inertial
system. The observer is at rest with respect to the table. I hope
this is clear. Now for the question:

HOW MUCH WORK DID THE BLOCK DO ON THE TABLE?

Well, Carl, you suggest and impossible situation and then give as the
only
answers wrong results.

In this proposed case the Earth is not an inertial system -- no matter
how
closely it approximates one. OK I give you no rotation if you like
for the
nonce but the Earth/table moves with respect to the CM of the
Earth/block
system.

And then you adopt the invention of pseudowork to deal with this
faulty
proposal.

The block does work on the Earth = negative work done on the block.

This is the same question as the ice skater pushing off and requiring
that
the rink be an inertial system and thus the work done on the rink = 0.
It
is not = 0

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen