Re: car acceleration

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

On the other hand, let's go back to the deformation idea.  While John D.
rejects this, it does seem to me that this has been used to preserve WE and
'real' work.  The 'reasoning' goes like this (I believe).  During the push
there MUST be some deformation of the wall.  That deformation may be very
small, but then the forces are very large.  Energy is stored in the deformed
wall BUT came from the person.  As the wall rebounds there is a force
(perhaps quite large) that acts through a displacement (perhaps quite small)
that will account for the change in KE of the person.  In the end analysis,
the energy does come from the person, but was temporarily stored in the
wall.  There will also be dissipative losses, but we can imagine those being
minimized.

If the above isn't complete nonsense, then there seems to be some
pedagogical advantages in maintaining a single WE approach.  I'm not really
against John's emphasis on momentum transfer, but I'm having trouble with
the mechanism by which the energy stored as chemical PE ultimately becomes
KE of the CM through only internal conversions.

Rick

----- Original Message -----
From: "Rick Tarara" <rtarara@saintmarys.edu>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, February 06, 2002 10:15 AM
Subject: Re: car acceleration


> Of course one might muddy the waters some more by considering that if the
> wall is _really_ rigid and is really rigidly attached to the earth, then
the
> push changes the rotational velocity and the rotational KE of the earth,
but
> I won't go there!   ;-)
>
> Rick
.