Re: physics of bouncing

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

At 08:32 AM 3/14/01 -0500, S.Goelzer wrote:

> After any real collision I do in my lab some of the energy is in the form
> of thermal energy,

OK.

> This is quite imperceptible to my students (other than the fact that the
> objects involved are going slower).

OK.

>  How do I demonstrate that the energy still exists in a different form
> (most intro. students are satisfied with a qualitative demo) ?

Good question.  See below.

> Is the burned paper/steel ball demo or the thermal card changing color
> demo proving this?

No, not in any way that I can see.

====================================

So.... We want to demonstrate the real physics of ordinary bouncing.  If we
want to use the card as an indicator, we need to set up a situation where
the card is more of a witness and less of a participant.

One way to move in that direction is this:
  1) On a hard floor (or anvil or whatever) make a stack of four or five
sheets of rubber.  Cut up old inner-tubes if there is no other convenient
source of rubber sheets.
  2) In the interstices between sheets, put pieces of thermal-indicator card.
  3) Pound on the stack a few times with a hammer.
  4) Open the stack to reveal the cards, which will indicate that the
rubber, throughout its bulk, has increased in temperature.

Many variations are possible.

========

Measuring the temperature rise of stirred air is also possible.