Re: MOMENT OF INERTIA

[Patrick Whippey <pwhippey@JULIAN.UWO.CA>]

At 06:36 PM 12/19/1998 -0500, you wrote:
> I am not sure what physical situation is referred to here. My previous
> message had to do with a book on a table, no acceleration.
>
> Friction can NEVER cause an increase in speed.

Hmmm.  Consider the case of the block on a table, being accelerated by a
string, say.  Now put a second block on top of the first.  The force that
accelerates this second block is the force of friction that the first block
exerts on the second.  Friction always opposes the motion, except when it
doesn't.


 Static friction only
> opposes outside forces and there is no motion at all (static). Once
> static friction is overcome (by some other outside force) and the body
> starts to move, friction is always opposite to velocity and slows the
> body down.
> J. Epstein
> > If the contact force is a vertical force (and I agree that it is), then it
> > cannot cause an acceleration in the horizontal direction.  The only force
> > in the horizontal direction is the friction force.  Therefore, it is
> > responsible for the horizontal acceleration.
Regards,

Patrick W. Whippey
Department         http://www.physics.uwo.ca
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