Uniform Circular Motion
Purpose: To investigate the relationship between force and velocity of an object moving
in a circle with a fixed radius.
Hypothesis:
Materials: string (1.5-2.0m), rubber stopper, timer, straw or pen cylinder, alligator
clip, 10 large washers, 1 large paperclip.
Procedure:
Assemble your apparatus so the rubber stopper tied to one end of the string will
rotate in a circle having a radius of 1m. Begin with 6 washers tied to the other end of
the string. While rotating the stopper at constant velocity, measure the amount of
time required for 20 cycles and record in a data table. Repeat this process adding 2
more washers (8 total) and then again for 2 more washers (10 total).
Data / Analysis:
# of washers
6
8
10
Mass (kg)
Time for 20 rev
Period (T)
Radial Force
Calculate and record the period for each amount of washers by dividing the
average time by the number of revolutions of the stopper. Determine the total mass of
each trial by multiplying the number of washers by their average mass and converting
to kilograms (kg). Calculate the force exerted by the washers by multiplying their total
mass by 9.8 m/s2 for each trial.
Plot a graph of Force (F) versus 1/T2. The graph should be linear since
centripetal force is inversely proportional to the square of the period (T). Calculate the
slope of the plot. The slope should equal a value close to m(4π2R) where m is the mass
of the stopper and R is the radius of its path.
This will verify the equation listed where centripetal force, F 
m4 2 R
.
T2
Write a conclusion stating any reasons for specific error as well as a lab summary and
whether or not your hypothesis was supported.