Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: mechanical equivalent of heat



Bernard Cleyet wrote:

in research 2ppm is common -- A Sr. thesis student at UCSC
recently built who study critical effects use these things.

Vernier's has (in your range of interest) 0.03 C deg. resolution.
http://www.vernier.com/probes/temp.html

Interesting. A book I have shows that the Iron-Constantan
thermocouple has the sensitivity of about 50 microvolts
per degree C at a room temperature.

Suppose the iron cylinder is replaced by the lead cylinder of
about the same size. This gives three times more dPE. The
specific heat of lead is about three times less than for iron or
steel. In this arrangement the single shot dT becomes 0.2 C
(instead of 0.018 C). The above thermocouple would show
a voltage change of 10 microvolts. How accurately can this
be measured with a commercial instrument?

Ten strokes ~ 15% resolution, a hundred -- 2% -- "doable".

Mount the tube on a slowly rotating wheel. Right?

Ludwik Kowalski wrote:

kyle forinash asked:

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. ...

Somebody who has access to a shop can produce something
like this. It is a sealed iron tube (3 kg) and an iron piston (10 kg)
inside, with some air. The piston can travel 1 meter from one
end to another; it has holes allowing air to sip during a vertical
fall. Suppose the tube, well insulated with styrofoam, has a
mechanical release system to trigger the fall of the piston. By how
much should the temperature increase? PE decreases by 98 J
producing 23.4 calories of heat. Assuming all of it goes to 13
kg of iron the expected dT is 0.018 degree (in a single shot).
Can such dT be measured with a thermister to within ~1%
accuracy? I do not know.