Projectile catcher, Step pulley, Part iii: determining the rotational inertia – PASCO ME-8950A COMPLETE ROTATIONAL SYSTEM User Manual
Page 17: Watch the digits display to see the velocity, Wind the thread up and hold the rotating platform, Record the slope in table 1.4, Photogate with pulley, Table 1.4 rotational inertia data
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Complete Rotational System
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Part III: Determining the Rotational Inertia
Setup
1. Attach a Photogate with a pulley and mounting rod to the
base using the black rod.
2. Connect the Photogate to a PASCO interface and connect
the interface to a computer.
3. Wind a thread around the middle step pulley on the center
shaft and pass the thread over the pulley.
Procedure
Accounting For Friction
Because the theory used to find the rotational inertia experi-
mentally 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. Start 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 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 Rotating Platform turns, stop monitoring data, stop
the Rotating Platform, 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 1.4.
Finding the Acceleration of the Apparatus
To find the acceleration, put about 30 g - record the exact hanging mass in Table 1.4 - 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 1.4.
Friction Mass
Hanging Mass
Slope
Radius
Table 1.4 Rotational Inertia Data
Projectile
Catcher
step pulley
Photogate
with pulley