Italian Physicist Galileo Galilei  was  born on February 15th 1564. He and his parents lived in Pisa for most of his childhood.

When Galileo was ten years old  he and his family moved to Florence where he was enrolled into the monastery of Vallombrosa.

One day whilst in the cathedral, Galileo sat looking at the ceiling lamp as it swung to and fro. He realized that no matter  the size of the swing, the pendulum took the same amount of time to make one full oscillation.

He was so fascinated by this fact, that he went home and experimented to better understand the effect that varying the amplitude had on the period of a pendulum.

It didn't end there though. He wanted to know what other factors  could be manipulated to produce a change in the period of a pendulum. 

So he conducted experiments which tested the effect  varying  the mass  and length would have on the period of a pendulum.