Pendulums

A pendulum is a weight hanging from a fixed point that swings back and forth. It always takes the same amount of time for each swing. This is what makes pendulums so useful for keeping time. Grandfather clocks use pendulums to tick at a steady pace.

How Pendulums Work

When you pull a pendulum to one side and let go, gravity pulls it back down. It swings past the center and up the other side. Then gravity pulls it back again. The pendulum keeps swinging back and forth. Each complete swing takes the same amount of time, no matter how big or small the swing.

What Affects a Pendulum

The length of the string or rod changes how fast a pendulum swings. A longer pendulum swings more slowly. A shorter pendulum swings faster. Surprisingly, the weight on the end does not matter. A heavy weight and a light weight on the same length string will swing at the same speed.

Fun Facts

• Galileo was one of the first scientists to study pendulums in the 1500s.
• The longest pendulum clock in the world has a pendulum over 70 feet long.
• A Foucault pendulum can demonstrate that the Earth rotates by slowly changing its swinging direction.

Did You Know?

In 1851, a French scientist named Leon Foucault used a giant pendulum to prove that the Earth rotates. The pendulum appeared to change direction, but it was actually the Earth turning underneath it!