PASCO ME-8950A COMPLETE ROTATIONAL SYSTEM - Manual (Page 43)

012-05293F Complete Rotational System
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Measurements For the Experimental Method
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 overcome
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. In the DataStudio program, select ’Smart Pulley (Linear)’ and set up a Digits display to show
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.
3. Start monitoring data, and then give the Rotational Disk 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 Rotational Disk turns, stop monitoring data, stop the
Rotational Disk, and adjust the amount of mass on the thread by adding or removing a paper clip.
6. Repeat the process until the velocity stays constant.
7. Measure the mass on the end of the thread and record it as the ’Friction Mass’ in Table 6.2.
Finding the Acceleration of Disk and Track
To find the acceleration, put about 50 g - record the exact hanging mass in Table 5.2 - 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 display of Velocity versus Time. The slope of the best fit line for your data
is the acceleration of the apparatus.
5. Record the slope in Table 6.2.
Mass of Disk
Radius of Disk
Distance Between
Parallel Axis
Table 6.1: Theoretical Rotational Inertia
Friction Mass
Hanging Mass
Slope
Radius
Fixed Disk and
Track Combined
Track Alone
Rotating Disk and
Track Combined
Table 6.2: Rotational Inertia Data