Sometime during the early 1580’s, a young Italian medical student by the name of Galileo Galilei (1564 – 1642) was attending Mass at the Cathedral of Pisa, when (according to legend) he noticed an attendant pulling a chandelier to the side in order to light its candles. When the attendant let go of the chandelier, it began swinging to and fro. Gradually the swings became shorter and shorter in distance, but the duration of the time of each progressively shorter swing seemed to remain constant (Figure 2A). This puzzled Galileo because one might assume that, as the swings become shorter in distance, the duration of the time of each shorter swing would also become shorter.
Galileo then went home and simulated what he had witnessed at church by tying a large stone to the end of a rope and suspending it from the ceiling. He then measured the duration in time of each swing of the stone to and fro by counting the beats of his heart, and sure enough, the time period of each swing appeared to remain constant even when each swing became very short.
When Galileo lengthened the rope, the duration of each swing became longer, but the longer duration remained constant as the distance of each swing became shorter (Figure 2B). When he shortened the length of the rope, the duration of each swing became shorter, but again the shorter duration remained constant in time (Figure 2C). When Galileo replaced the original stone with a heavier one and then with a lighter one, there was no apparent difference in the above results (Figure 2D). Galileo concluded that the duration in time of each constant swing depends only upon the length (distance) of the rope, and that the weight or mass of the suspended stone was of no consequence to the duration of the swing. Several decades later, Newton would employ another accelerating pendulum experiment in an attempt to test Galileo’s conclusions. Newton experienced the same results and was just as bewildered as Galileo.