Re: Pb

[brian whatcott <inet@INTELLISYS.NET>]

I suspect that this interesting demonstration may possibly be
sailing under false colors. I understand that temperature
indicating cards feature a thin film of temperature sensitive
liquid crystal. If you apply enough pressure, I fear that the
liquid will be squeezed out with a conseqential color change
no matter what the temperature.

As a check, using a press to slowly apply pressure from a cooled
ball onto such a card might demonstrate some interesting color
 change also.

Brian

At 11:30 3/9/01 -0500, Scott Goelzer wrote:
> To demo this kind of transformation I drop a steel ball onto a one of
> the temperature sensitive color changing post cards (the Exploratorium
> sell these). The card must be on a hard floor.  A color change occurs at
> the point of impact. Pressing the ball against the card and  floor with
> great force and effort causes no change in color. Dropping the ball on a
> piece of wood with the card in between also causes no change in color.
> Demo leads to great student discussion regarding where energy is being
> transferred.
>
> HTH
> Scott
> *****************************
> Scott Goelzer
brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!