Pendulum Notes: History of Pendulum
(The following is background material
you should read prior to performing the experiments.)
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
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:
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.