Re: Pb

["John S. Denker" <jsd@MONMOUTH.COM>]

At 11:52 AM 3/9/01 -0700, Jim Green wrote:

> Please state any assumptions in you reply.

> Suppose I drop a piece of lead. The Earth, via gravity, does positive work
> on the lead and increases its KE.  OK?

OK.
...assuming we are measuring things in the usual laboratory frame.
...assuming we can neglect air resistance, sound, electromagnetic fields,
lunar and solar gravity, and about a hundred other things.

>  The lead hits the floor; the lead halts. KE->0  OK?

OK so far.
...assuming special lead that is just squishy enough to come to rest
without bouncing, without splattering, et cetera.
...assuming the floor is not deformed by the interaction.
...assuming we can neglect the small momentum and small^2 energy
necessarily transferred to the earth.
...assuming we can neglect various non-necessary energy transfers.
...and about a hundred other things.

> the flood does negative work on the lead;

Not OK at all.

In the stipulated reference frame, the floor does not move.  Therefore
        W_floor = F_floor dot d(x_floor) = 0

> Does Wgravity = Wfloor?

Not even close.

> Why is the lead heated?

Because one part of the lead does work on another part of the lead.