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Re: PseudoWork ????



Too stupid to stay out of these,

But is there really any problem here? The energy transformations are
internal to me, but these enable me to exert a force on the wall. That
force is countered by a force of the wall on me. In order to 'push off' I
must apply the force DURING a time interval in which my CM moves--I have to
bend my arms. Therefore the wall produces a force on me that acts over a
distance (the movement of my CM while in contact with the wall) which then
changes my kinetic energy. The wall seems to act as an intermediary in this
process of converting chemical potential energy (foodstuffs) to bulk KE, my
movement. I don't remember what Jim's model was, but this seems OK to me.
The only question is, can the wall exert a force on me without moving (a
tiny bit)?

Rick




----- Original Message -----
From: Bob Sciamanda <trebor@VELOCITY.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, October 29, 1999 11:28 AM
Subject: Re: PseudoWork ????


I don't think this will do, Jim. Your model must also apply to the
limiting case (mass of earth/wall => oo)!
In this limit, the wall is stationary, but I (the pusher) still gain CM
kinetic energy from only energy sources/transformations inside myself!

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: Jim Green <JMGreen@SISNA.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, October 29, 1999 12:51 PM
Subject: PseudoWork ????


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.
. . . Jim