Re: [Phys-l] heat/energy

["John Clement" <clement@hal-pc.org>]

I can get an increase in hand or foot temperature by mentally thinking about
putting them into a hot bath.  I am not kidding.  Meditation exercises put
one into a state where you can learn how to change body temperature in the
extremities.

The hand rubbing is a convincing demo even if it is a cheat.  Most of the
warm feeling probably comes from increased circulation.  But students never
think of that.  So the transfer of kinetic energy to thermal is something
they actually already understand.

The real trick is to get them to consider it when looking at energy balance
situations.  But there using bar charts helps a lot.  The big difficulty is
getting students to transfer this idea to problems.  They can see any number
of physical situations where mechanical energy decreases, but then they
can't tell you that it transferred to thermal or internal energy.  The
energy interactive lecture demos in the Active Physics Suite may help a bit.
I always suggest using them rather than conventional demos because they have
been researched and refined to produce better gain.

I would suggest just sawing a board with a hand saw.  While an electric saw
will get a more dramatic effect, they can't accuse you of cheating with a
hand saw.

John M. Clement
Houston, TX

> Just tried this--got about a 2 degree Celsius increase in temp by rubbing
> my
> hands together for 30 seconds.  Just measured by holding a thermometer
> between my hands in a 'praying' position.