Re: ENERGY WITH Q

[Jim Green <JMGreen@SISNA.COM>]

> A block slides to rest along a level rough table. The only net force
> on the block is kinetic friction. The table is clamped to the floor
> and hence to the earth. We approximate the earth as being an inertial
> system. The observer is at rest with respect to the table. I hope
> this is clear. Now for the question:
>
> HOW MUCH WORK DID THE BLOCK DO ON THE TABLE?

Well, Carl, you suggest and impossible situation and then give as the only
answers wrong results.

In this proposed case the Earth is not an inertial system -- no matter how
closely it approximates one.  OK I give you no rotation if you like for the
nonce but the Earth/table moves with respect to the CM of the Earth/block
system.

And then you adopt the invention of pseudowork to deal with this faulty
proposal.

The block does work on the Earth = negative work done on the block.

This is the same question  as the ice skater pushing off and requiring that
the rink be an inertial system and thus the work done on the rink = 0.  It
is not  = 0

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