Pendulum

physics · motion · gravity · timing

What it is. A pendulum is simply a weight hanging from a string or rod that swings freely. Gravity is the invisible force that keeps pulling it back to the middle, no matter how far you push it to the side.

The perfect timer. The time it takes a pendulum to swing left and then right again is called its period. Amazingly, this time stays almost exactly the same every time, which is why pendulums were used in old clocks to keep perfect time.

Length matters most. A longer pendulum swings more slowly and takes longer to complete one cycle, while a shorter pendulum swings faster. This is why a pendulum's period depends mostly on how long the string is.

It keeps going. Once you swing a pendulum and let it go, it will keep oscillating back and forth without you having to push it anymore. Gravity and the string always bring it back to swing the other way.