Re: mechanical equivalent of heat

[Bernard Cleyet <anngeorg@PACBELL.NET>]

first this is what I sent the originator (a mistake) of the thread:

cut--

I think UCSC Phys. uses glass!

An insulated tube with some heat capacity is OK.

If the temp. is determined accurately, a small temp change reduces loss to the
outside world.
That's why I think a metal tube is good.  I would insulate it by suspending it
in a larger plastic
tube and filling the space with expanded poly-urethane (available in a
pressurized can from
the local hdw. -- NOT home depot.)  I made a "Dewar" using urethane and two
paper cups
for (as) a test of it's effectiveness.  It held liq. N2 nearly as well as a
std. vacuum Dewar!
Then use the method of mixtures to determine the "actual" heat capacity and
the cooling
curve.  You also already use the std.: start below ambient and stop when you
reach the same
temp. diff. above?

I recommend doing the expt. (and the calibration before hand) using a
thermocouple ot (sic)
thermister continuously recorded a la Vernier.

bc

kyle forinash wrote:

   Bernard Cleyet wrote:
   >
   > Yea, $400 is outrageous.  I must ask the lower div. lab. mgr. about "our"
crank
   > apparatus -- I think our shop made it.

   Or you can spent $800 for the deluxe model from CENCO ...

 cut --
  >
   > bc
   >
   > P.s. Is your tube metal, plastic, or glass and insulated?   The L.D. lab
uses
   > only one with a number of other apparatuses, including the shot one, for
that
   > lab period as stations.  The students rotate in pairs doing all of them.
   >
   > kyle forinash wrote:
cut  --

A cheap (both senses) DMM (bench not battery)  has a claimed resolution of 10
microV.  This is for the 200 MV range.   The "accuracy" is 0.05% + 2 digits
(least significant of 4 1/2)

If you have an e-shop, they can make an op-amp.  thermocouple amplifier, feed
it to a Radio Shack DMM that has RS-232 output to your IBM, and you'll have
it.  Most commercial thermometers (Fluke) have only 0.1 degree resolution.
Here's one that will do your job well, but I doubt it's < $1k.

http://www.sbir.com/thermometers.htm

Most researchers use RTD's as TC's are noisy, less linear, etc.

bc

when I was a student we used pots. The Leeds &  Northrop K-2 has a resolution
of one microvolt, but cost, what? $1k in 1950 (you could buy a good used car
for that!)



Ludwik Kowalski wrote:

> 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.