PS-3220
Experiment 2: Rotational Inertia of Disk and Ring
19
013-15949A
Procedure
Measurements for the Experimental Method
A. Finding the Acceleration of the Ring and Disk
1.
In the data collection software, create an experiment to measure the angular velocity (in radians per second)
versus time (in second) of the ring and disk.
•
In PASCO Capstone, for example, drag the Graph icon from the Displays palette to the workbook. Select
“Angular Velocity (rad/s)” for the vertical axis, and “Time (s)” for the horizontal axis.
•
Click the Hardware Setup icon in the Tools palette to open the “Hardware Setup” panel. In the panel, click the
properties button (it looks like a gear wheel in the lower right corner).
•
In the Properties window for Linear Accessory, select the size of the 3-step Pulley you are using. The default
setting is “Large Pulley (Groove)”. Click OK.
2.
Put a 50-g mass on the Mass Hanger and turn the 3-step Pulley to wind up the thread so the hanger is just
below the Super Pulley. Hold the 3-step Pulley.
3.
Click Record to begin recording data, and release the 3-step Pulley, allowing the hanger to fall.
4.
Caution! Click Stop to end data recording BEFORE the hanger reaches the floor or the thread completely
unwinds from the 3-step Pulley.
5.
In the Graph display, select the region of the data that represents when the ring and disk were accelerating.
6.
In the Graph display, select “Linear” from the curve fit menu.
The slope, m, of the linear fit represents the angular acceleration
(
) for the Point Mass and Apparatus
7.
Record the value of the slope, m, as the angular acceleration in Data Table 2.
Data Table 2: Experimental Rotational Inertia Data
C. Finding the Acceleration of the Disk Alone
1.
In “Finding the Acceleration of Ring and Disk,” both the disk and the ring are rotating; therefore, it is necessary
to determine the acceleration and the rotational inertia of the disk by itself so this rotational inertia can be sub-
tracted from the total, leaving only the rotational inertia of the ring.
2.
Take the ring off the apparatus and repeat the steps under “Finding the Acceleration of the Ring and Disk” for
the disk alone. Record the results in Data Table 3.
Calculations
3.
Calculate the experimental value of the rotational inertia of the ring and disk together, and record the value in
Data Table 3.
Ring and Disk
Combined
Disk Alone
Hanging Mass
Slope, m
Radius
