Re: mechanical equivalent of heat

[Alan Levin <TSM2001@EROLS.COM>]

I still do the Joule tube (the falling shot experiment) and get somewhat
poor results but what I'm looking for is the concept of potential energy -
kinetic energy turning into heat.

I'm not sure what the 'calorimeter on a crank' apparatus is but there is a
piece of equipment that we call a stand kit.  It consists of a cylinder of
aluminum that has a cord around it.  Two unequal masses (one falling and the
other rising) are attached to the cord.  The friction with the aluminum
causes that falling mass to move rather slowly.  The potential energy,
kinetic energy and heat are accounted for and the Joule constant is
determined.  This also "works" poorly but again the concept is the thing..

When I am in the mood for something that "works" I take out this old
electric coffee pot that I only use for this demonstration.
Starting with 1000 grams of 20° C water I tell the students that I wish to
bring the water just up to 100°C.  They calculate the number of calories of
heat needed to do this (80,000 calories).  The pot is a 1000 watt appliance
or 1000 joules/second or 239 calories/sec.  They do the calculations and 334
seconds later the water has reached the predicted temperature.  The best
part is that this pot makes an awful lot of noise while in the brewing phase
prior to getting to the "boiling point" it then gets quiet. I don't know
what the cut off mechanism is but it happens right on time and makes a fine
demonstration.

Alan Levin
Columbia High School
Maplewood, NJ




kyle forinash wrote:

> Does anyone have a simple mechanical equivalent of heat laboratory
> exercise (1st year undergrad level)?
>
> I know of two; lead shot falling in a tube (which has horrible accuracy)
> and the 'calorimeter on a crank' appratus (pretty costly). I don't like
> either. Does anyone know of any others worth doing?
>
> kyle
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