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Swing Low: Investigate the Motion of a Pendulum

Time Required Very Short (≤ 1 day)
Prerequisites None
Material Availability Readily available
Cost Very Low (under $20)
Safety No issues


"Swing me higher, Mommy, higher!" Kids love to ride the swings at the playground. The back-and-forth motion of a swing demonstrates the physics of a pendulum. In this experiment, you will investigate the factors that affect the speed and duration of a pendulum's swing.


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?


La Né Powers

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MLA Style

Science Buddies Staff. "Swing Low: Investigate the Motion of a Pendulum" Science Buddies. Science Buddies, 20 June 2014. Web. 28 July 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p016.shtml>

APA Style

Science Buddies Staff. (2014, June 20). Swing Low: Investigate the Motion of a Pendulum. Retrieved July 28, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p016.shtml

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Last edit date: 2014-06-20


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 and Concepts

  • pendulum
  • gravity
  • momentum
  • friction


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


  • 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

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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 these 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
    Total Time
    Average Period
    Average Total Time
    35 1        
    70 1        

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  • 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?

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