PASCO ME-9341 INTRODUCTORY ROTATIONAL APPARATUS - Manual (Page 21)

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012-03051F Introductory Rotational Apparatus
Experiment 4: Frictional Torque
EQUIPMENT NEEDED:
- Introductory Rotational Apparatus
- Smart Pulley with rod and table clamp (another pulley will work, the photogate is not
needed)
- Mass hanger with mass set
- Thread
- Meter stick.
Introduction
In order to apply Newton's equations of motion, all the forces acting on the system under
investigation must be known. In any mechanical system, however, there are usually unmea-
sured frictional forces, so it often appears as if the motion of the system is not in complete
accord with Newton's laws.
In this lab, you will use a falling mass to provide a torque that will rotate a platter. The
energy lost by the falling mass will supply the rotational kinetic energy of the spinning
platter. Then, as the mass is pulled back up by the platter, the platter will again slow down,
its kinetic energy transformed back into the gravitational potential energy of the rising
mass. However, the mass will not rise all the way to its original height, because some
energy has been lost due to friction. By assuming that energy is conserved in this system,
you will determine the amount of frictional torque acting in the Introductory Rotational
Apparatus.
Procedure
➀ Set up the apparatus as
shown in Figure 4.1,
with the step pulley on
top. Then use the
bubble level to level
the apparatus.
Note: In this
experiment the Smart Pulley should be mounted on the lab
table far enough from the apparatus to keep the tread angle
from the spindle to the pulley as small as possible. If the angle
is too great the thread will snap as the mass is pulled back by
the platter and the thread rewinds on the spindle.
➁ Attach a 1.5 meter piece of thread to the step pulley and wind it
up on the smallest of the three spindles. Measure and record r,
the radius of the spindle, in Table 3.1. Attach the mass hanger
so that when the thread is fully extended the hanger will not
reach the floor. Extend the thread and measure h
o
, the distance
from the floor to the mass hanger.
➂ Place 100 grams on the hanger, and record the total mass, m, in the data table.
Figure 4.1 Equipment Setup
h
1
h
o
h
2