Re: ENERGY WITH Q

[kowalskil <kowalskil@MAIL.MONTCLAIR.EDU>]

There are many good questions in Carl's message. Let me
address one of them.

"Carl E. Mungan" wrote:
> I posed this question the other day and I have not seen
> an answer yet. Here it is again. I stop a block with a
> string. No change in the block's thermal energy occurs.
> Now I stop the block via sliding friction. The block's
> thermal energy changes. Why does friction change the
> thermal energy of an object but tension does not (in
> these particular situations)?

String:
Your block slides horizontally without friction. It is
intercepted by a string. The KE of the block is converted
into Eth, most of it is initially in your string.

Friction:
Once again KE is converted into Eth, but this time about
half of it goes initially into the floor and another half
into the block.

The main point is the 100% KE --> Eth conversion, not
how the H=deltaEth is distributed at any particular
moment. If you wait long enough (in a perfectly sealed
room) then the final outcome should be the same in both
cases, a change of temperature of everything in that
room by 0.0000...1 C.

I know that you know this. I am emphasizing that your
two cases lead to identical final outcomes. You are
asking why there is a difference, I am saying there
is no difference.

If your room is your system then Esys=KE+Eth remains
the same. Somebody else would say the internal energy
remains the same. I view this as an example of total
(100% efficient) conversion of non-thermal into thermal.
Ludwik Kowalski