PASCO ME-8950A COMPLETE ROTATIONAL SYSTEM - Manual (Page 32)

Complete Rotational System 012-05293F
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Procedure
Accounting For Friction
Because the theory used to find the rotational inertia experimentally does not include friction, it will
be compensated for in this experiment by finding out how much mass over the pulley it takes to over-
come kinetic friction and allow the mass to drop at a constant speed. Then this “friction mass” will be
subtracted from the mass used to accelerate the apparatus.
1. Start the DataStudio program. Select ’Smart Pulley (Linear)’ and set up a Digits display to how
velocity with three significant figures.
2. Hang a small amount of mass (such as a few paper clips) on the end of the thread that is over the
pulley. Make sure that the thread is wound around the step pulley.
3. Start monitoring data, and then give the Rotating Platform a tap to get it started moving.
4. Watch the Digits display to see the velocity.
5. If the velocity increases or decreases as the platform turns, stop monitoring data, stop the plat-
form, and adjust the amount of mass on the end of the thread.
6. Repeat the process until the velocity stays constant.
7. Measure the mass on the end of the thread and record it as ’Friction Mass’ in Table 4.2..
Finding the Acceleration of the Apparatus
To find the acceleration, put about 30 g - record the exact hanging mass in Table 4.2 - over the pulley.
In the DataStudio program, set up a Graph display of Velocity versus Time.
1. Wind the thread up and hold the Rotating Platform.
2. Let the Rotating Platform begin to turn and at the same time, START recording data.
3. Let the mass descend toward the floor but STOP recording data just before the mass hits the floor.
4. Examine your graph of velocity versus time. The slope ("m") of the best fit line for your data is
the acceleration (use Fit>Linear Fit). Record the slope in Table 4.2.
Repeat the procedure for the mass at the inner stop. Record results in Table 4.2.
Measure Radius
1. Using calipers, measure the diameter of the step pulley about which the thread is wrapped and
calculate the radius.
2. Record the radius in Table 4.2.
Friction Mass
Hanging Mass
Slope
Radius
Mass at Outer Stop Mass at Inner Stop
Rotational Inertia
Table 4.2 Rotational Inertia Data