PASCO ME-8950A COMPLETE ROTATIONAL SYSTEM - Manual (Page 20)

Complete Rotational System 012-05293F
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Once the linear acceleration of the mass (m) is determined, the torque and the angular acceleration can
be obtained for the calculation of the rotational inertia.
Setup
1. Level the rotating platform.
2. Attach the square mass (point mass) to the track on the rotating platform at any radius you wish.
3. Mount the Photogate/Pulley system to the base and connect the photogate through an interface to
a computer. See Figure 2.2.
4. Attach a thread to the middle step of the step pulley and hang the thread over the 10-spoke pulley.
Allow the string to reach to the floor.
Procedure
Part I: Measurements For the Theoretical Rotational Inertia
1. Weigh the square mass to find the mass M and
record in Table 2.1. Why is it possible to assume
that the square mass acts the same as a point mass?
2. Measure the distance from the axis of rotation to the
center of the square mass and record this radius in
Table 2.1.
Part II: Measurement 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 ring.
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.
10-spoke pulley with
photogate head
300g mass
rotating
platform
"A" base
Mass, M
Radius, R
Table 2.1: Theoretical Rotational Inertia
Figure 2.2: Rotational inertia of a point mass