Swing Time

Starring

You and Your Students!

Script By

Vicki Cobb, Education World Science Editor

Synopsis

A playground swing is really a timing device!

Genre

Physical Science

Required Props

• playground swings
• stop watch (optional)

Setting the Scene (Background)

The nice weather is upon us and kids are spending more time outside. Why not send them to the playground with a problem to solve? All they need are swings and a provocative question.

Stage Direction

Show-Biz Science is scripted by popular children's book writer Vicki Cobb. Click to learn more about Vicki or to read a brief synopsis of her philosophy of teaching science. Visit our archive of archive of Show-Biz Science Activities. Watch for a new activity each week. Then chat with Vicki -- share your feedback and ask your questions about teaching science -- on our special Showbiz-Science message board. Be sure to visit Vicki's Kids' Science Page for more great science fun, a complete list of her books, and information about how you can invite Vicki to come to your school. And don't miss her library of science videos too. Or visit Vicki and other great authors of nonfiction for children at the INK Think Tank.

Take a guess: In a swinging contest, who do you think would take longer to make two complete swings: a pumped-up-high swinger or a gently swaying rider?

Pose that question to your students. Get them to take a vote. It's ok if they guess wrong, because science is about making discoveries -- and you can make discoveries even when you guess wrong.

PLOT

Act I
Some things must be seen to be believed, and this is one of them

For this experiment, your students can use two swings side by side or a single swing. If you use two swings, it is important that their ropes or chains be the same length. It is not necessary that the swingers be the same weight (although some kids might find this confusing and another experiment can be designed to see if the weight is a variable). Use a watch that times seconds or count off the seconds by saying, "One chimpanzee, two chimpanzee" and so on.

Get both swings going -- one high and fast, the other slow and low. Then have the riders quit pumping and let the swings move naturally. Time how long it takes for each rider to return to the place each started from. That means that if you start timing from the highest forward position, then you finish when the swing is again at that position.

Amazingly, there are no winners here. But there are no losers either. Big arc swings and little arc swings take exactly the same amount of time.

Behind the Scenes

To understand what is going on, you have to get physical. To a physicist, a swing is simply a pendulum. The time it takes for the pendulum to make one complete to-and-fro swing is called its period. The period of a pendulum is affected only by the pendulum's length. The distance it moves or the weight it moves has absolutely no effect.

Before mechanical clocks were invented, the Italian physicist Galileo discovered this law of pendulum motion. He noticed a swinging lamp in church and timed its period by using his pulse. He found that the period of the lamp remained the same even as it slowly decreased the distance it swung. This seemingly useless bit of trivia was later used by clockmakers. Pendulums became the basis for measuring time. (It's a good thing Galileo didn't get too excited by his discovery. If his heart rate had speeded up, the march of science might never have been the same.)

Article By Vicki Cobb
Education World®
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