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Project Summary

Difficulty	2
Time required	Very Short (a day or less)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	No issues

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Objective

The goal of this project is to investigate the motion of a simple pendulum. How is the motion of the pendulum related to its length?

Introduction

A pendulum is an object, hung from a fixed point, that swings freely back and forth under the action of gravity. A playground swing is an example of a pendulum. The swing is supported by chains that are attached to fixed points at the top of the swing set. When the swing is raised and released, it will move freely back and forth. The swing is moving due to the force of gravity on the swing. The swing continues moving back and forth until friction (between the air and the swing, and between the chains and the attachment points) slows it down and eventually stops it.

Terms, Concepts and Questions to Start Background Research

• pendulum
• gravity
• momentum
• friction

Questions

• What is a pendulum and what causes it to swing?
• What are some common uses for pendulums?

Bibliography

• Introduction to General Physics Concepts:
  Hewitt, Paul G. 2002. "Conceptual Physics," Prentice Hall, IL.
• Simple Physics Concepts for Kids:
  Keller, R.W. 2005. "Real Science for Kids: Physics, Level 1," Gravitas Publications, Inc., NM.

Materials and Equipment

• 2 identical chairs
• string or yarn
• 10 metal washers of identical size
• book
• meter stick
• scissors
• stopwatch accurate to 0.1 s
• an assistant

Experimental Procedure

1. Place the two chairs less than 1 meter apart, back to back.
2. Center the meter stick and lay it on the backs of the two chairs.
3. Cut one piece of string to a length of 70 cm.
4. Cut another piece of string to a length of 35 cm.
5. Tie the two lengths of string to the meter stick, toward the middle of the stick. The strings should be about 20–30 cm apart.
6. Attach 5 washers to the end of each string.
7. To conduct the experiment, hold the washers tied to the 70 cm long string in one hand and the washers tied to the 35 cm long string in the other hand.
8. Pull the strings tight and hold the strings at the same angle from the meter stick.
9. Have an assistant ready with a stopwatch. Start the stopwatch at the same time that you drop the two pendulums.
10. Time how long the pendulums swing.
    1. How long does it take each pendulum to swing back to its original position? This is the period of the pendulum.
    2. What is the total time that each pendulum swings?
    3. Note that, unless you have two stopwatches, you will need to do separate trials for each of the above measurements.
11. For any experiment, it is important to do multiple trials to assure that your results are consistent. Repeat steps 7–10 for at least five separate trials for each length of string, and record your results. It will be easier to keep track of your results if you write them down in a table in your lab notebook. Here is an example table for data collection:
    

    Sample Data Table
    Pendulum Length (cm)	Trial (#)	Period (s)	Total Time (s)	Average Period (s)	Average Total Time (s)
    35	1
    	2
    	3
    	4
    	5
    70	1
    	2
    	3
    	4
    	5

Variations

• Instead of changing the length of string, change the number of weights attached to the string. Does mass affect the speed of the swing or how long the pendulum swings?
• Does the initial angle of the string affect the speed and duration of the swing?
• Change the size of the washers. Does the size affect the speed and duration of the swing?

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

La Né Powers

Last edit date: 2006-02-22 00:49:34

Career Focus

If you like this project, you might want to think about career opportunities in Physics.

Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy. Learn more about this career: Physicist.