Re: Work/Energy theorem ?

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Fri, 4 Apr 1997, Mark Shapiro wrote:

> 	You may feel the force of gravity while standing on the surface of
> the earth.  I, on the other hand, feel my body in perfect equilibrium
> owing to the balance between the gravitational force and the
> electromagnetic forces that give by bones structure....  In other words, I
> don't feel myself being accelerated....(ok I will admit to a very small
> centripetal acceleration owing to the earth's rotation.)

Mark,

Is this to say that you disagree with the thrust of my last post? Perhaps
I'm misreading you. You aren't seriously suggesting that the person on the
train is any different are you?  What could it posssibly mean to "feel
yourself being accelerated" that is any different from how you "feel" when
you are standing on the ground?  Do you really mean to imply that there is
some way for the person on the train to distinguish between the "forces
from deceleration" (as you called them in your first post) and what we
generally refer to as a "gravitational force"?

(Just to make sure we stay on topic here let me acknowledge that the
*real* gravitational force *is* distinguishable via its nonuniformity (the
tidal effect.  In fact that is the only thing about the gravitational
force that gives it any genuine physical significance.  However, this
tidal effect is irrelevant to the issue at hand because it is far too
small to "feel" and isn't taken into account in standard work-energy
treatments of near earth phenomena of the type we are discussing here.) 

John
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