Pendulum Notes: History of Pendulum

(The following is background material you should read prior to performing the experiments.)

 Galileo: measuring periods, heartbeats, pulses and clocks

Galileo was a brilliant scientist who lived in the fifteenth and sixteenth centuries. It is thought that one day in 1581, in Pisa Cathedral, Galileo observed a lamp hung on a long chain. As he watched the lamp swing back and forth he noticed that it didn't matter whether the lamp swung a long way or a short way, it took the same amount of time to go back and forth. The time it takes a pendulum to complete one swing is called its period.

Pendulums are useful because they can accurately measure time. But why do pendulums act so predictably? We will answer that question much the same way Galileo did more than 500 years ago. (For references for this material, please visit Educational Resources.)

Pendulums are mentioned in both Galileo's Dialogue Concerning Two Chief World Systems and his Dialogues Concerning Two New Sciences. In these two works, Galileo discusses the following major points about pendulums:

  • The period is independent of the bob weight.
  • The period is independent of the amplitude.
  • The square of the period varies directly with the length.

For one experiment described in Two New Sciences, string lengths of four or five yards are suggested. The original experiments also used lead and cork balls.

The measurement of time was a major issue in many of Galileo's experiments. For his pendulum experiments, he seems to have compared the pendulums in pairs over the same time. For example, a person would be assigned to each pendulum of the pair and between the words "start" and "stop" each would count the number of times it swings back and forth, also called its oscillations.

To begin your explorations of pendulums, you also will count how many oscillations occur in a thirty second time frame as you vary the length of string and types of weights on a pendulum.

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