Name(s): ________________________________________________ Period: _______________
Pendulum motion has been studied for centuries for its special properties. Galileo observed a swinging lantern and made and important discovery about the timing of a pendulum swing. A Dutch man named Christiaan
Huygens discovered the relationship between the length of a pendulum and the time it takes to make a complete swing, which led to the use of pendulums in clock making and keeping time. It was the most accurate way to keep time until the 1930s!
Materials Needed:

Calculator

Piece of Thread/String

3 coins of all the same denomination (3 quarters, 3 nickels, or 3 pennies)

Metric Ruler or Measuring Tape

2 Medium Binder Clips

Stopwatch
Activity 1: Creating Your Pendulum

Tie a medium binder clip to the end of a piece of string. The binder clip will be used to hold one or more coins for the experiments in Activity 2.

The weight on the end of the string (the binder clip and the coin(s) it holds) is called the pendulum bob

The period of the pendulum is the time it takes for the pendulum to complete one full swing (back and forth)
Activity 2: Investigating Weight
This will be your first experiment. Your goal is to try and determine whether or not the weight attached to the end of the pendulum affects the time it takes for the pendulum to make one full swing.
1.
Make a prediction: Do you think the weight will affect how long it takes the pendulum to make one full swing? Explain why or why-not (using complete sentences)
2.
Experiment:
Tape your pendulum to the table top. This must be done in a way that neither the string nor the bob touch any other object when it is swung.
Insert one coin into the binder clip
Measure the length in centimeters from the point where it is attached to the table to the center of the bob. Record this length:

Length of the Pendulum: _______________
Pull the pendulum back to an angle of about 20 degrees and let it go (use some frame of reference so that you are pulling the pendulum back at the same angle for every trial).
Using the stopwatch, record how many seconds it takes for the pendulum to complete 10 full swings (back and forth) in the table below.
Repeat steps (d) and (e) two more times (three trials total)
Find and record the average times to complete 10 swings for each number of coins in the table below.

Name(s): ________________________________________________ Period: _______________
Divide the average by 10 to figure out the period of the pendulum for each amount of coins.
Record the period in the table below.
Trial 1
One Coin Two Coins Three Coins
Trial 2
Trial 3
Average time to complete 10 full swings
Period of Pendulum
3.
Reflection: Based on your data that you collected, does it appear that the weight of the bob affected the period of the pendulum? What factors other than the weight might have affected the period of the pendulum for each trial?
Activity 3: Investigating the Length
This is your second experiment. Your goal is to try and determine whether or not the length of the string affects the time it takes for the pendulum to complete one full swing.
1.
Make a Prediction: Do you think the length of the string will affect how long it takes the pendulum to make one full swing? Explain why or why-not (using complete sentences)
2.
Experiment:
Cut a second string that is half the length of the original string.
Repeat experiment one exactly. Record your results in the table below
Trial 1
One Coin Two Coins Three Coins
Trial 2
Trial 3
Average time to complete 10 full swings
Period of Pendulum

Name(s): ________________________________________________ Period: _______________
3.
Reflection: Based on your data that you collected, does it appear that the length of the string affected the period of the pendulum? Explain.
Activity 4: Analyzing
The formula l

980 t
2
4

2 represents the length l (in centimeters) of a simple pendulum with a period of t seconds.
(In this formula, the acceleration due to gravity is given as 980 cm/ s
2
.)
1.
Using the above formula, solve for t . Simplify and rationalize the denominator!! a) How might this formula for t be more useful than the one given? b) According to the formula, how does changing the weight of the bob affect the period of a pendulum? Does this observation match the results you found in your first experiment?
2.
Use the formula to find the theoretical period for each pendulum. Record your experimental and theoretical periods for each:
Experiment 1
Experiment 2
Length of Pendulum Experimental Period Theoretical Period a)
Do you’re experimental results give the same periods as the theoretical models? b) What factors do you think would account for any differences? Explain your observations.