It was a typical Sunday in 1581. Hundreds of worshippers filled the huge cathedral in Pisa, Italy. Most of them listened intently to the church service.
But not seventeen year-old Galileo Galilei. Instead, Galileo studied a chandelier hanging overhead. Air currents flowing through the lofty cathedral moved the chandelier from side to side, back and forth. Sometimes the chandelier moved gently; sometimes it swung in a wide arc. No matter what the size of its swing, it seemed to Galileo that the chandelier kept steady time.
There were no clocks or watches in those days. To time the chandelier’s swings, Galileo felt for the pulse in his wrist. He counted the pulse beats. One, two, three beats for one swing. One, two, three beats for another.
Galileo was surprised. No matter how wide or narrow the swing, it always took the same number of pulse beats. Right after the service, Galileo raced home. He quickly suspended a weight from a long string to create a pendulum. Galileo pulled the weight back a short distance, released it, and timed its swing. He tried it again, this time pulling the weight back farther before releasing it. After many tries, Galileo confirmed his suspicions – the time it took to make one swing was always the same whether the swing was wide or narrow.
Excited now, Galileo tried other experiments with his pendulum. He discovered that the length of string, amount of weight, and other factors all had some predictable relationship to the time of a pendulum’s swing.
Some years later, Galileo experimented with falling objects. Did all objects fall at the same rate? To find out, he needed to time objects as they fell. But that posed a problem. How could he accurately time something that moved so quickly?
Galileo remembered the pendulum. The weight of the pendulum acted just like a falling object – except it didn’t fall straight down. It fell on a slant and at a slower rate that could be timed.
Galileo adapted the pendulum as a timepiece. First he got a wooden board and carved a long, straight, smooth groove down the center. When he raised the board slightly at one end and released a ball, it slowly rolled down the groove.
Galileo marked off his grooved board into small divisions of equal length. For a timing device, he rigged up a water-filled container with a small hole in the bottom. By counting water drops, he could keep track of time. Now he was ready to begin.
He released one ball at a time from the higher end of the board. As the balls rolled, Galileo timed how long it took them to cross each division of the board. To his surprise, Galileo discovered that the balls didn’t travel down the track at an even rate. Instead, they accelerated – or sped up – as they got farther down the groove. Falling objects, he found, picked up speed as they fell to the earth.
After more experiments, Galileo was able to work out a mathematical formula to calculate the acceleration of a falling object. To prove his point, he even predicted how far a cannonball could be blasted from a cannon. Then he fired it to verify his prediction.
In many ways, the swinging chandelier started a revolution in the world of science. With his pendulum investigations, Galileo pioneered the scientific method –the system of carefully controlled experiments and observations that modern scientists use today to prove a natural law beyond a shadow of a doubt.