Name: _______________________
Date: _____________
Partners: _________________________
Per: ___
Pendulum Lab
Purpose: To determine what effect different variables will have on the period of a pendulum.
Materials:
1.5 m string
meter stick
ruler
stop watch
masking tape
protractor
hanging masses
books
Predicting:
What effect do you think each of the following will have on the period of the pendulum? Explain
what you think will happen and why.
Part I: Determine how the length of the string (L) changes the period of a
pendulum.
Procedure:
1. Tie a 100g hanging mass to a piece of string.
2. Tie the string to a ruler so 1 meter of string hangs down
3. Tape the ruler to the table top so the string can hangs down without touching anything.
4. If the bottom of the string touches the floor, raise the ruler on a stack of books and tape it
down.
5. Release the mass from a 15° angle.
6. Allow it to complete one swing and then time how long it takes to complete 20 swings.
7. Enter your data in the table below.
8. Repeat steps 5 &6.
9. Repeat with the various lengths of string.
10. Calculate your average for each length of string.
Data Table 1:
Length (m)
Trial 1
1
.8
.5
.2
Period (sec)
Time for 20 swings
Trial 2
Average
Period2
(sec2)
Avg. Per.
for Class
(sec2)
Class
Average2
(sec2)
11. Graph the length of string vs. period, include your data and class average (there will be
two sets of points). Place the length of the string along the x-axis and the period along the
y-axis. Name this Graph 1 Length vs. Period.
12. Graph the length of string vs. period squared for your data and the class average. Name
this Graph 2 Length vs. Period2.
Questions for Part I:
1. How do your results compare to the class average? Explain.
2. How do the curves in Graph 1 compare to Graph 2?
3. Which graph provides the most valuable information? Explain.
Part II: Determine how the mass of the bob changes the period.
Repeat steps 1-10 from the procedure in part I, using 1 meter of string, starting at a 15° angle,
but vary the mass of the bob, using the masses in the data table.
Data Table 2:
Mass
(g)
Time for 20 swings
Trial 1
Trial 2
Average
Period
Period2
Avg. Per.
Class
(sec)
(sec2)
for Class
Average2
(sec2)
(sec2)
50
100
200
300
Construct a graph of the mass verses either period or the period2. Name your graph “Graph 3Mass vs. Period”.
Part III: Determine how the amplitude changes the period.
Repeat steps 1-10 from the procedure in Part I, using 1 meter of string, a 100g, and vary the
amplitude by changing the angle from which the bob is released.
Data Table 3:
Angle
Time for 20 swings
Trial 1
Trial 2
Average
Period
Period2
Avg. Per.
Class
(sec)
(sec2)
for Class
Average2
(sec2)
(sec2)
15°
45°
60°
90°
Construct a graph of the angle verses either the period or the period2 for your data and the
class average.
Post-Lab Questions:
1. Identify the controls and the variables from Part I. Explain.
2. Identify the controls and variables from Part II.
3. Identify the controls and variables from Part III.
4. What relationship exists between period and length of the string, mass, and angle of
release? Explain. You should reference your data and your graphs in your conclusion.
Going Further:
A. Calculate the slope of the line for your data of length of string vs. period2. The equation
for slope is rise/run or y2-y1/x2-x1. (Show your work)
B. Use the slope of the line to estimate the period of a pendulum that is 27 cm long.
C. Estimate the period of a pendulum that is 5 meters long.
Going Even Further:
A. Calculate the potential energy of the pendulum using the formula PE=mgh. You will have
to use your pendulum to make some measurements.
m = mass (g)
g = gravity = 9.8 m/s2
h = height = height above the center where the pendulum would have if not
swinging. (m)
B. What would the potential energy be at the bottom of the swing (lowest point)? Use the
formula to prove your answer.