SWINGING PENDULUM (Length)
PURPOSE
Construct a pendulum and determine whether the length
of the pendulum affects the number of swings of that pendulum in a given
time.
PERFORMING THE EXPERIMENT
-
Suspend a pendulum from the notch in the iron ring
on the ring stand by placing a hook in the notch over the ring. Then suspend
the metal washer on the hook at the bottom end of the thread.
-
Using a meter stick or tape, measure the length of
your pendulum in centimeters from the top edge of the iron ring to the
center of the washer. On the data sheet nearby, write your first and last
name, and record the length of the pendulum.
-
Ask your adult partner to hold the base of the ring
stand firmly as you perform the experiment.
-
Pull the washer and thread forming your pendulum
out to about a 45º angle. Ask your adult partner to tell you when
the second hand of the watch or clock reaches the minute mark. Release
the washer exactly at that time. NOTE: Do not push the pendulum; simply
release it. Both of you should then count the number of swings back and
forth until exactly 30 seconds have passed. Back and forth count as separate
swings. Do not lose count! Record your result on the data sheet, repeat
the experiment and record your results. Calculate and record average number
of swings in 30 seconds.
-
Repeat Steps 1-4 with the other 3 pendulums.
-
On the graph paper provided nearby, plot number of
swings in 30 seconds versus length of your pendulum by reading up on the
vertical axis until you come to your number of swings, reading across the
graph horizontally until you come to your length of pendulum, and then
placing a small circle on the graph. Your adult partner may need to assist
you in plotting your results. Your circle will not be on either axis. Do
you observe any trends or patterns based on your data or on all data plotted
so far?
QUESTIONS TO THINK ABOUT
1. What force pulling on the washer caused it to
fall when you released the pendulum?
2. Did the speed at which the pendulum moved differ
during its swing? At what point was it moving fastest? At what point was
it moving slowest?
EXPLANATION
Galileo first performed this experiment by observing
swinging lamps in a cathedral and timing them with his pulse beat. He found
that the time for one swing increases by a factor of two if the length
of the pendulum is multiplied by four, or decreases by one-half if the
length of the pendulum is reduced by one-fourth.
EQUIPMENT NEEDED
Ring stands and iron rings; various lengths of thread
up to 84 centimeters (33 inches) with Christmas ornament hooks at each
end; meter stick; metal washers of the same mass; watch with second hand
or a clock in the room with second hand
REFERENCE
Modified from Janice Pratt VanCleave, Physics
for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines,
and Sound, Wiley, New York, NY, 1991, page 76.
SWINGING PENDULUM (LENGTH) Data Sheet
| First and Last Name |
Length (centimeters) |
Number of swings
in 30 seconds |
Average number of
swings (2 values)
in 30seconds |
|
|
|
|
SWINGING PENDULUM (LENGTH) GRAPH
|
