PASCO ME-9341 INTRODUCTORY ROTATIONAL APPARATUS User Manual
Page 33
012-03051F
Introductory Rotational Apparatus
29
Exp 4 – Frictional Torque - Notes and Data
Introduction
This lab is easy and requires no sophisticated electronic equipment. The greatest source of error in this experi-
ment is in measuring the highest point reached by the hanging mass when the spinning platter pulls it back up.
Resist attempts to talk about the friction of the system, unless you also attempt to identify the effective radius at
which the frictional force is applied.
Alternatives
The students give the platter a spin and measure an initial angular velocity. They then count the number of
revolutions until the platter comes to a stop. From the total angle through which the platter rotated,
θ
, they could
determine the torque using
τθ
= RKE , where RKE = 1/2 I
ω
2
= the rotational kinetic energy of the platter.
Notes – on Procedure
➀ Setting up the apparatus with the spindles down will allow you to test the frictional torque with different
masses if desired. Make sure that the pulley is at an appropriate height so that the string will wind onto the de-
sired step automatically.
➃ The frictional torque has been shown to be somewhat dependent on the angular velocity of the base plate.
Since the difference in height that the weight drops affects this velocity, the original height of the weight will
affect the frictional torque measured.
➅ Again, because the friction is dependent on velocity, the mass used will affect the measured friction. The mass
will also affect the friction of the pulley used for support. The greater the mass used, the greater the magnitude
of the measured frictional torque.
Notes – on Analysis
D a t a
D a t a
D a t a
D a t a
D a t a
Mass (kg)
r (m)
h
0
(m)
h
1
(m)
h
2
(m)
h
2
(m)
h
2
(m)
B.P. + pulley
0.02523
0.015
0.12
0.651
0.505
0.495
0.430
0.07548
0.015
0.115
0.651
0.572
0.562
0.572
0.12586
0.015
0.112
0.651
0.594
0.595
0.595
0.17610
0.015
0.106
0.651
0.602
0.602
0.604
0.19674
0.015
0.103
0.651
0.605
0.600
0.603
B.P. only
0.09662
0.015
0.115
0.651
0.575
0.575
0.575
0.14683
0.015
0.113
0.651
0.582
0.580
0.581
0.19722
0.015
0.082
0.651
0.598
0.600
0.600
B.P. + disk
0.19722
0.015
0.102
0.651
0.595
0.595
0.595
Data