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Discover the Law of the Pendulum



THE PENDULUM
When Galileo was about eighteen years old, he attended a cathedral in Pisa. The lamplighter walked from chandelier to chandelier, lighting them in the growing dusk. As the lamplighter reached up with his torch and pushed against each chandelier to light the flames, the chandeliers began swinging back and forth.

Galileo watched as a large chandelier swung back and forth after it had been lit. The swings were very long at first, and Galileo decided to time the duration of each swing by counting his pulse. He noted the number of heartbeats it took for each swing. Gradually, the chandelier slowed down and each swing was shorter. It was then that Galileo made an important discovery.

Galileo realized that it took exactly the same amount of time for the duration of each swing of the chandelier no matter whether it was a long swing or a short swing. Galileo had discovered the law of the pendulum and how each swing of a pendulum is isochronal, or occurring at equal intervals.

As usual, Galileo wasn’t satisfied with his discovery until he documented countless experiments to prove it. He left the cathedral that day and launched many experiments testing this new law. After recording his own measurements from his experiments, he began showing others the results. Everyone was amazed with the discovery!

DISCOVER THE LAW OF THE PENDULUM
Using a simple weight hanging from a string, Galileo demonstrated the law of the pendulum to pupils as well as teachers at the University of Pisa, asking them to time the swings with their own pulse.

MATERIALS
Household string
High beam in open space such as a swingset
Plastic bucket with handle
Beanbag or plastic bag filled with dried beans

Cut a piece of string long enough to hang from the beam to the ground. Tie one end of the string to the beam. If it is too high for you to reach, tie one end of the string in a loop with an overhand knot. Toss the looped end over the beam and within reach. Slip the other end through the loop. Tighten the loop up against the beam.

Tie the bucket to the end of the string so the bucket hangs freely off the ground. Place the beanbag in the bucket to give it weight. You have now made a simple pendulum. To begin the experiment, pull the bucket back as far as you can reach. Let the bucket go. Time each swing according to your pulse.