# A swinging good time with pendulums

Pendulums:  To and Fro We Go

Today’s lesson focused on the motion of pendulums. The motion of pendulums was one of the many phenomena investigated by the famed scientist Galileo over 400 years ago and what he learned about them had a huge impact on the history of technology. The periodic motion of pendulums allowed for the invention of clocks and the standardization of time, and they still have many uses in modern society such as seismographs.

Students saw that a pendulum consists of a pivot point with a rope or wire attached to it and a mass on the end. The time it takes the pendulum to make one full oscillation back and forth is called the period. Here, gravity is the only force working on the pendulum. If we took the same pendulum and put it on the Moon, the pendulum would have a slower period due to less gravitational force. Some examples of items that use pendulums are metronomes and grandfather clocks.

For the activity, students had to determine whether the mass, length of the chain, or angle of the swing affects the period of a pendulum. They did this by constructing their own pendulums and then changing the variables one at a time. After a lot of very careful trials and calculations, they were surprised to learn that only length caused the period to change: a longer chain correlated to a longer period. The mass does not affect the period because, as they learned last visit, gravity works on different masses in the same way. If the angle affected the period, they would have seen a longer period as the angle increased, which was not the case.

The students worked really well within their groups to conduct the pendulum trials and everyone came to the same conclusion. In the end we revealed a mathematical formula that would have saved them from doing so much work to find the answer, but seeing is believing!

To experiment with virtual pendulums at home, check out: