PHYSICS 23 LABORATORY
O5: Rotation with constant α
NAME:
DATE:
Partner’s Name:
Laboratory Instructor:
Recitation Section:
Laboratory Section:
Recitation Section:
Spring 07
OBJECTIVES: Determine the moment of inertia, I, of a disk by measuring the angular
acceleration, α, when a constant toque is applied.
Reading:
Introduction: This week in class you are learning about rotation and how it is analogous
to one dimensional linear motion. Remember to go from linear motion equations to
rotational motion equations, translate from Latin to Greek. For example:
LINEAR
F = ma
Mass = m
position = x(t) (one dimension )
velocity = v = dx/dt
acceleration = dv/dt = d2x(t)/dt2
a = constant
THEN
v(t) = v0 + at
x(t) = x0 + v0t + ½ at2
ROTATIONAL
Torque =  = Iα = r× F = r F sin β
Moment of Inertia = I
angular position = θ(t)
Angular velocity =  = d/dt
Angular acceleration = d/dt =
d2(t)/dt2
α = constant
THEN
(t) = 0 + αt
(t) = 0 + t + ½ αt2
Apparatus:
Procedure: Open DataStudio and setup to measure using the rotational apparatus. Set it
up to use the Rotational Dynamics Apparatus with graphs for position, angular velocity
and acceleration. Attach a table to the angular velocity. NEVER rotate the apparatus
unless the air supply is on and the pressure gauge reads over 6 psi. The pinchcock at the
right hand side of the apparatus should be open so the bottom disk does not rotate.
Release the hanging mass and start recording. Stop before the hanging mass reaches the
end of its fall and reverses.
Measurements: Paste a plot of (t) vs. t and a table of (t) vs. t here
Mass of Disk:
Diameter of Disk:
Diameter of pulley:
Analysis: Determine the angular acceleration α by fitting the appropriate curve to your
(t) vs. t curve.
Calculate the torque assuming F = mHANGING g. If you need help measuring r, ask your
lab teacher. Calculate the moment of inertia of the disk from your measurements of α.
Calculate the moment of inertia of the disk from your measurements of its mass and
diameter (neglecting the moment of inertia of the pulley.) How do the two results
compare?
Now change the size of the pulley and repeat the above.
Conclusions:.
1. Do your measurements support α = constant? Explain.