User's Manual

®
8
3. Hang the following masses over two of the super pulleys and clamp the pulleys at the given angles.
Procedure (Experimental Method)
By trial and error, find the angle for the third super pulley clamp and the mass that must be suspended over the pul-
ley so that its weight will balance the forces exerted on the strings by the other two masses. This third force is
called the equilibriant (F
E
) because it establishes equilibrium. The equilibriant is the negative of the resultant.
Record the mass and angle for the third pulley to put the system into equilibrium into Table 1.1.
To test whether the system is in equilibrium, use the following criteria.
Method of Finding Equilibrium
The clear disk will be centered in the String Tie when the system is in equilibrium. Pull the clear disk slightly to
one side and let it go. Check to see that the disk returns to the center. If not, adjust the mass and/or the angle of the
super pulley clamp until the disk always returns to the center when pulled slightly to one side.
Analysis
To theoretically determine what mass should be suspended over the third pulley, and at what angle, calculate the
magnitude and direction of the resultant by the component method and the graphical method. The equilibriant
(F
E
) will have the same magnitude, but it will be opposite in direction. In other words, the direction will be 180°
from the direction of the resultant.
Component Method
On a separate sheet of paper, add the vector components of Force A and Force B to determine the magnitude of the
equilibriant. Record the components R
x
and R
y
in Table 1.2. Use trigonometry to find the direction of the equilib-
riant (remember, the equilibriant is exactly opposite in direction to the resultant.) Record the results in Table 1.2.
Graphical Method
On a separate sheet of paper, construct a tail-to-head diagram of the vectors of Force A and Force B. Use a metric
ruler and protractor to measure the magnitude and direction of the resultant. Record the results in Table 1.2.
Remember to record the direction of the equilibriant as opposite in direction to the resultant..
R
x
= ______________ R
y
= ______________
Table 1.1:
Force Mass Angle
F
A
50 g (0.050 kg) 0°
F
B
100 g (0.100 kg) 120°
F
E
Table 1.2:
Equilibriant (F
E
)
Method Magnitude Direction
Experimental
Component
Graphical