PASCO TD-8551A MECHANICAL EQUIVALENT OF HEAT - Manual (Page 9)

012-04331E Mechanical Equivalent of Heat
5
➤NOTE: When the cylinder is cold, water may
condense on its surface. Dry the cylinder
thoroughly with a cloth or paper towel before
wrapping the rope, so that all of the heat goes
into heating the cylinder and not into evaporating
the condensed water.
⑧ Set the counter to zero by turning the black knob
on the counter.
⑨ Watch the ohmmeter carefully. When the
resistance reaches the value corresponding to
your starting temperature, start cranking (clock-
wise, facing the crank side of the apparatus).
➤ IMPORTANT: There should be only enough
turns of rope around the cylinder so that the
frictional pull on the rope is just enough to lift the
hanging mass about 3 cm off the floor - no
higher! To accomplish this, wrap the rope three
or four turns and crank. Add turns as needed to
support the mass while cranking with only very
slight tension on the free end. Attach the rubber
band to the free end of the rope. Now, without
cranking and while keeping the rope taught by
the rubber band, tie the other end of the rubber
band to the eyebolt on the baseplate. If you find
that the large hanging mass continues to rise
more than 3 cm as you turn the crank, remove
one turn from the cylinder nearest the free end. If
the large hanging mass continues to rest on the
floor, add another turn of rope around the
cylinder at the free end.
Crank rapidly until the temperature indicated by
the thermistor is 1° C less than your designated
stopping temperature, then crank very slowly
while watching the ohmmeter. When the
temperature reaches your stopping value, stop
cranking. Continue watching the ohmmeter until the thermistor temperature reaches a maximum
(the resistance will be a minimum) and starts to drop. Record the highest temperature attained as
your final temperature.
➉ Record N, the number on the counter—the number of full turns of the crank.
11 Measure and record m, the mass of the aluminum cylinder.
12 With a pair of calipers, measure D, the diameter of the aluminum cylinder. Record the radius of the
cylinder in the worksheet ( R = D
2
).
Figure 8 Hook up the Ohmmeter
Ohmmeter
Banana Plug
Connectors
Friction
Rope
Hanging
Mass
3 - 6 Turns of Rope
Figure 9 Add Friction Rope and Hanging Mass
Cylinder (front view)
Constant
Tension on
free end
Rubber Band
Hanging Mass
on this end
Base