User's Manual

012-05293F Complete Rotational System
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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 thread by adding or removing a paper clip.
6. Repeat the process until the velocity stays constant as the mass falls.
7. Measure the mass on the end of the thread and record it as the ’Friction Mass’ in Table 2.2.
Finding the Acceleration of the Point Mass and Apparatus
To find the acceleration, put about 50 g - measure the exact mass and record it in Table 2.2 - on the
end of the thread over the pulley. In DataStudio, set up a Graph display of Velocity versus Time.
1. Wind the thread up and hold the Rotating Platform.
2. Let the platform begin to turn and at the same time, start recording data.
3. Let the mass fall 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 ’Linear Fit’ for your
data is the acceleration of the apparatus.
5. Record the slope in Table 2.2.
Measure the 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 2.2.
Finding the Acceleration of the Apparatus Alone
Since in Finding the Acceleration of the Point Mass and Apparatus the apparatus is rotating as well
as the point mass, it is necessary to determine the acceleration, and the rotational inertia, of the apparatus
by itself so this rotational inertia can be subtracted from the total, leaving only the rotational inertia of
the point mass.
1. Take the point mass off the rotational apparatus and repeat Finding the Acceleration of the
Point Mass and Apparatus for the apparatus alone.
NOTE: that it will take less “friction mass” to overcome the new kinetic friction and it is
only necessary to put about 20 g on the end of the thread over the pulley.
2. Record the data in Table 2.2.
Calculations
1. Subtract the “friction mass” from the hanging mass used to accelerate the apparatus to determine
the mass, m, to be used in the equations.
2. Calculate the experimental value of the rotational inertia of the point mass and apparatus together
and record in Table 2.3.
3. Calculate the experimental value of the rotational inertia of the apparatus alone. Record in
Table 2.3.
Friction Mass
Hanging Mass
Slope
Radius, r
Point Mass and Apparatus Apparatus Alone
Table 2.2: Rotational Inertia Data