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M o d e l N o . M E - 9 5 0 2 E x p . 5 A : C e n t e r o f M a s s
0 1 2 - 1 2 8 7 6 B 25
Exp. 5A: Center of Mass
Equipment Needed
Theory
Gravity is a universal force; every bit of matter in the universe is attracted to every other bit of matter. Therefore,
when the Balance Arm is supported by the pivot, every bit of matter in the Balance Arm is attracted to every bit of
matter in the Earth.
Fortunately, the sum of all these individual gravitational forces produces a single resultant. This resultant acts as if
it were pulling between the center of the Earth and the center of mass of the Balance Arm. The magnitude of the
force is the same as if all the matter of the Earth were located at the center of the Earth, and all the matter of the
Balance Arm were located at the center of mass of the Balance Arm.
An object thrown so that it rotates tends to rotate about its center of mass,
and the center of mass follows a parabolic path. An object whose center of
mass is above a support tends to remain in rotational equilibrium (bal-
anced on the support). In this experiment you will use your knowledge of
torque to understand and locate the center of mass of an object.
Setup
Measure and record the
mass of the beam.
Next, find the mass of
two of the protractors
and record the masses.
(Note that you can use
the Spring Scale to
measure the mass.)
• Beam = ________
• Protractor 1 = __________
• Protractor 2 = __________
Loosen the thumbscrews on the two protractors and slide one onto each end of the beam so each protractor is at the
165 mm mark. Tie a mass hanger to the thread on the angle indicator of each protractor
Mount the Balance Arm near the center of the Statics Board.
Record the total mass of the beam plus protractors plus mass hangers (5 grams each).
• Mass of system = _____________
Item Item
Statics Board Balance Arm and Protractors
Asymmetrical Plate Thread
Mass and Hanger Set
Support
Center of mass
Object
Figure 5.1: Equipment Setup
M
1
M
2
Pivot
base
Protractor
Angle
Indicator