SIMPLE PENDULUM
OBJECTIVE
To understand the relationship between the period and the length of a
simple pendulum.
EQUIPMENT
Balance, 1-meter string, 2-pendulum bobs, lab post, pendulum apparatus,
timer w/ gate.
PROCEDURE
- Measure and record the mass of each pendulum bob. Insert the lab
post into the table and clamp the pendulum apparatus to this post.
Attach the pendulum apparatus to the lab post and suspend the
pendulum bob. There is a clamp with a thumbscrew you can use to
suspend the bob. This will allow the pendulum to oscillate about a single
point. Align the pendulum bob at each of your lengths of thread so that
the bob passes through the photogate to permit a period measurement. - Set the apparatus so that the length of the pendulum is between 5 and
80 cm. Accurately measure and record the length you use. For these
measurements, you should keep the amplitude of oscillation small, less
than about 10° (estimated by eye). Select measurement for Time, set the
mode to pendulum. Start the bob swinging, in an arc of about 10
degrees. At the extreme of the swing press start. The meter will display
the time for one complete cycle. Note, one cycle is defined as the
motion that returns the bob to its original position and velocity. - Measure and record the time required for the bob to complete a cycle
(the period) at least 10 times. It is best if you start the bob swinging, make
sure it is smooth, and then start recording. Starting the swing can
introduce other oscillations, which may affect your readings. Thus, it is
best to measure your data with only one release. - Measure the period of the pendulum using a variety of different
pendulum lengths ranging from 5 cm to 80 cm. Choose as least 7 different
lengths in this range. Your choices should span the entire range. - Repeat the entire experiment for the second pendulum bob.
GRAPHS AND DIAGRAMS - Plot the pendulum length versus the square of the period
- Make a free body diagram showing all the forces acting on the
pendulum bob when the pendulum is at the maximum in swing.
QUESTIONS - What is the expected relationship between the length of a simple
pendulum and its period? Does your data follow the expected trend? - From graph 1, determine g, the acceleration of gravity. Is this a good
way to determine g? What limits your precision? Does your value of g
agree with the expected value? - Did the mass of the bob have an effect?
- Instead of using the timer to measure the period of many individual
oscillations, how would you find the period with good accuracy using a
stopwatch?