PseudoWork ????

[Jim Green <JMGreen@SISNA.COM>]

At 05:23 AM 29-10-99 -0400, Bob Sciamanda wrote:
> Yes, Jim.  This is why I say that when you push off from a stationary
> wall, the wall does work, even though the resulting energy of bulk motion
> came only from internal sources, not from the wall!

Well, Bob, when someone says that he agrees with, you it is hard to
disagree with him. (:-)
Some want tp call this pseudowork we agree tht this is not helpful.  But I
would add the it is also true that there is no such thing as a stationary
wall.  If the pusher moves, so does the wall.  Now given the mass of the
wall plus the Earth to which it is attached, the wall does not move very
much, but it does move.  The wall does indeed do work on the pusher.

Yes, the wall does no work on the pusher's hand (which do not move with
respect to the wall, but the hand bones are  connected to the ulna bone
which is connected to the humerus which shoulder bone which is connected to
the .... and each force does work because the body _does_ move with respect
to the wall.

The list has previously gone over this ad nauseum.  And we would agree I think.

It is also true that energy does not move!  The resultant energy of the CM
of the body arises not from "internal energy", but because Work was done on
it.  Yes, in the present case chemical and perhaps thermal internal energy
is decreased in the process of this work - but likely this is what you meant.

I would like to say that in no case is there an increase of mechanical
energy (I really would like to say energy of any kind but I have not
thought that through) unless work is done on the system -- but surely
someone will give a counter example -- I look forward to it. (:-)

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