Metro Community College
Physics 1010
Lab Write Up
Name ___________________
2/8/2016
Pendulum Periods
When Christopher Columbus sailed for America he had two
navigational tools at his disposal: the magnetic compass and
the sextant. The compass gave him the direction and the
sextant gave him the angle of the sun.
By pointing the sextant south and keeping the sun at the same
angle, Columbus could follow the same latitude around the
globe to get to India, unfortunately, America was in the way
The English noticed the regular rate
of the swing of the pendulum. A
clock that kept Greenwich Time was
placed aboard ship. By comparing
noon aboard ship to Greenwich
Time, you could measure your
longitude.
Sun
With longitude and latitude determined, you knew your location on the ocean and could sail anywhere
at will. English ships using a clock, a compass, and a sextant, conquered the seas and built the English
Empire.
This lab checks the accuracy of the pendulum’s period which was the basis of the ship’s clock.
Preliminary Questions
1. String variations – Varying one aspect of the experiment is often helpful in understanding the
relationships involved. Measuring the period using your pulse or just visual observation vary the
parameters below and note if you detect a difference.
a. Length of string:
When the length of the string is increased, the period increases or decreases. (Circle
correct choice)
b. Amplitude of swing:When the amplitude increases, the period. Increases or decreases. (Circle correct
choice)
c. Mass of the pendulum bob:
When the mass of the pendulum bob is increased, the period increases or decreases.
(Circle correct choice)
MCC Physics 1010 Lyle A Sass
Page 1 of 5
2/8/2016
Metro Community College
Physics 1010
Lab Write Up
Name ___________________
2/8/2016
Additional Materials




Timer
Tape
Graph paper
Erector Stands
Procedure
1. Use the Erector Stand instead of the ring stand to hang the 200 gram mass. The arrangement in
the lab works well. We will not be using the photo gate. We will be timing the period instead.
Steps 2 – 5 are based on the Vernier equipment that we are not using. Use the alternate steps
below.
2. One person will be timing the run with a timer. Another person will be counting the number of
oscillations. One oscillation is leaving and returning to the starting position.
3. After 20 – 30 oscillations call time and find the average period by dividing the time elapsed by
the number of oscillations.
4. There are three variations you will be measuring the period for:
 Length of string
 Amplitude of swing
 Mass of pendulum bob
5. Two trials for each variation are essential. For example, for the string length variation, you will
want to measure the period for the several lengths of string in two trials. You may do more trials
if you choose. A group of five runs will provide a good basis for the average period.
MCC Physics 1010 Lyle A Sass
Page 2 of 5
2/8/2016
Metro Community College
Physics 1010
Lab Write Up
Name ___________________
2/8/2016
Data Table
Amplitude of Swing
Use a 200 gram pendulum bob and a 50 cm string length.
Amplitude
Elapsed Time
Counts
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
5˚
30˚
Average period =
Amplitude
Elapsed Time
Counts
5˚
Average period =
Length of String
Use a 200 gram pendulum bob and amplitude of 20˚.
Length
Elapsed Time
Counts
1m
.9
.8
.7
.6
.5
Average period =
Length
Elapsed Time
Counts
Average period =
MCC Physics 1010 Lyle A Sass
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2/8/2016
Metro Community College
Physics 1010
Lab Write Up
Name ___________________
2/8/2016
Mass of pendulum bob
Use a 1 m string and amplitude of 20˚.
Mass
Elapsed Time
Counts
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
𝑃𝑒𝑟𝑖𝑜𝑑 =
𝐸𝑙𝑎𝑝𝑠𝑒𝑑 𝑇𝑖𝑚𝑒
𝐶𝑜𝑢𝑛𝑡𝑠
200 g
Average period =
Mass
Elapsed Time
Counts
Average period =
Analysis
1. The period is: (Circle the correct answer.)
a. The time elapsed from when the bob swings from one side to the other
b. The time elapsed from when the bob swings from one side across the center and back
to its starting position.
2. Graph the pendulum period versus the amplitude. Set the origin as (0,0).
Does the period depend on the amplitude?
3. Graph the pendulum period versus the length of the string. Set the origin as (0,0).
Does the period depend on the length of the string?
4. Graph the pendulum period versus the mass of the pendulum bob. Set the origin as (0,0).
Does the period depend on the mass of the pendulum bob?
Is there enough data to know?
MCC Physics 1010 Lyle A Sass
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2/8/2016
Metro Community College
Physics 1010
Lab Write Up
Name ___________________
5. Use the table below for calculations:
Run
Length
2/8/2016
Period
Length2
Period2
Make a graph of Period2 versus the length of the string using the calculations above.
Make a graph of Period versus (the length of the string)2 using the calculations above.
Compare the pendulum period versus the length of the string to these two graphs.
Which graph shows a direct proportion, that is a straight line gong through the origin?
6. The following equations can be derived from Newton’s Laws for some pendulums:
𝑙
𝑇 = 2𝜋√
𝑔
𝑇2 =
4𝜋 2 𝑙
𝑔
Does one of your graphs support the second equation?
Since the acceleration of gravity are constant, the period of a fixed length pendulum is constant and can
be used in a timepiece.
Extension
Attempt one of the extensions in the lab.
MCC Physics 1010 Lyle A Sass
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2/8/2016