Physics 40S
Centripetal Force & Period – Lab
Introduction: Acceleration is defined as the rate of change of velocity. The velocity of a body
changes if either its speed or its direction changes. Since the direction of the velocity vector
changes when a body moves in a circle at a constant speed, it is accelerating and according to
Newton’s Law, force is required to produce this acceleration. The force acting on a body moving
in a circle causing this acceleration is called the centripetal force.
NOTE: DO NOT hand in this sheet with your lab. All labs must be written
up in the proper order and organized properly. Include your data table,
but make up your own as part
of your write-up.
radius
Part 1:
Purpose: To study the relationship
between the centripetal force (Fc) and
the period of revolution (T) of a body
moving in a circular orbit of constant
radius.
Apparatus:
Method:
1. With a single rubber ball attached,
pull the cord through the glass until the
center of the ball will rotate in an orbit
of radius 100 cm. Attach an alligator clip
to the cord just below the glass tube.
Hang 5 washers on the string using a
bent paper clip to support them.
Paper clip or tape
washers
3. Swing the upper end of the glass tube
in an orbit of radius less than 3 cm, increasing the frequency until the cord moves up through the
tube. Maintain the frequency that keeps the upper alligator clip about 1 cm below the bottom of the
glass tube. Determine the time for 20 revolutions of the ball and record.
4. Repeat the procedure adding 5 washers each time until a total of 30 units of force are on the
bottom of the cord. Record the time for 20 revolutions in each case. Determine the period and the
period squared. (table – 4 marks)
Centripetal
force (no. of
washers) (Fc)
5
1.
Fc
time for 20
revolutions
time for 1
revolution
(T)
Period squared
(T2)
10
15
20
25
30
5. Plot a graph of T2 vs. Fc
T2
Fc
(2 marks)
6. Describe the shape of the graph obtained. Note that this is
not a linear relationship. (1)
1
7. Graph T2 vs.
. Is this more like a linear fit? (3)
Fc
T2
1
Fc
Part II
Purpose: To determine the relationship between the period (T) of a uniform circular motion, and
the radius of the motion.
Apparatus: Centripetal Force Apparatus as Part I
Procedure:
1. In this experiment, the mass that undergoes UCM is fixed at 1 stopper and the value of the
centripetal force is fixed at 12 washers.
2. With a radius of motion of 0.2 m measure the time for 20 revolutions, and record in the table.
Calculate the period (T) and also T2.
3. Repeat for radii of 0.4 m. 0.6 m, 0.8 m, 1.0 m (3 marks)
radius (m)
time for 20 revs.
period (T)
T2
4. Draw a graph of period 2 vs. radius (T2 vs. R). Is this linear (3)
T2
Part III
R
Purpose: To determine the relationship between the period (T) of a UCM and
the mass (m) of the revolving object. Mass is measured in this case by number of stoppers.
Apparatus: same as previous part.
Procedure:
1. In this part, the alligator clip should be adjusted so that the radius of revolution is 100 cm; and
the value of the centripetal force is also fixed at 15 washers.
2. With one rubber stopper on the end of the string, measure the time for 20 revolutions, and record
in the table. Calculate the period (T) and also T2.
3. Repeat for 2, 3 and 4 stoppers. (3)
no. of stoppers
(mass)
time for 20 seconds
period (T)
4. Draw a graph of period2 vs. mass (T2 vs. m). Is this linear (3)
T2
m
T2