PASCO TD-8551A MECHANICAL EQUIVALENT OF HEAT - Manual (Page 8)

Mechanical Equivalent of Heat 012-04331E
4
➤ IMPORTANT:
➀
For best results, read this procedure through thoroughly before
attempting the experiment
➁
A tube of powdered graphite lubricant is supplied with the
equipment. Spraying the aluminum cylinder lightly with this
before beginning the experiment will greatly reduce the wear
on the aluminum surface.
➤ NOTE: An experimental worksheet is provided at the end of
this section for recording data and calculations.
➀
Clamp the apparatus securely to the edge of a level table or
bench, as shown in Figure 7.
➁
Unscrew the black knob and remove the aluminum cylinder.
Place the cylinder in a refrigerator or freezer, or pack it in ice,
to bring the temperature down to at least 10 C° below room
temperature.
The cylinder is cooled so that, when it is heated by friction, the midpoint of the high and low
temperatures will be at room temperature. In the first half of the experiment, therefore, heat
will be transferred from the room air into the cooler cylinder. As the cylinder heats beyond
room temperature though, heat will be transferred out of the cylinder back into the room
atmosphere. By letting the change in cylinder temperature be symmetrical about the room
temperature, the quantity of heat transferred to and from the cylinder and room should be
approximately equal.
➂ While the cylinder is cooling, plan the desired temperature variation of the experiment. Ideally,
the temperature variation of the cylinder should be from 7-9 C° below room temperature to the
same amount above room temperature. Therefore, measure and record the room temperature,
and then determine and record the initial and final temperatures you wish the cylinder to reach
during the experiment. (You can record your data on the data sheet provided at the end of this
section.)
➃
Using the table of Resistance versus Temperature for the thermistor, determine the resistance
value which will correspond to each of your recorded temperatures. (A table covering most
temperature ranges is listed on the apparatus. A more complete table can be found near the end
of this manual.) Also determine the resistance measurement which corresponds to 1 C° below
the final temperature. You will want to start cranking more slowly as the temperature ap-
proaches this point, so that the final, equilibrium temperature will be close to your chosen final
temperature.
➄ When the cylinder is sufficiently cool, slide it back on the crank shaft. Be sure that the copper
plated board is facing toward the crank. Also make sure that the pins on the drive shaft fit into
the slots on the plastic ring on the cylinder, then replace the black knob and tighten securely.
➅ Plug the leads of the ohmmeter into the banana plug connectors as shown in Figure 8. Set the
ohmmeter to a range that is appropriate to the thermistor resistances that correspond to your
chosen temperature range.
➆ Wrap the nylon rope several turns around the aluminum cylinder (4-6 turns should work well)
as shown in Figure 9. Be sure that the rope lies flat against the cylinder and hangs down the
slot provided in the base plate. Tie one end of the rope, the end nearest to the crank, to the 10
kg mass as shown.
Unscrew Knob and remove Cylinder
Figure 7 Clamp to Table and
Remove Cylinder
Experiment: Measuring the Mechanical Equivalent of Heat