Friday, 2 August 2013

Battle of the Sciences: Physics

Third in a series of articles discussing which scientific discipline was responsible for the most significant scientific discovery. Today, Sampad Sengupta argues for Physics. 

When speaking of experiments in physics, most people nowadays would think of dark matter research and space exploration. However, I believe some of the most influential experiments in physics have been conducted over 300 years ago when all this technology was not available and the human brain was one’s greatest tool.

Galileo Galilei was an Italian physicist, mathematician, astronomer and philosopher, born in February 1564 in Pisa, Italy. He conducted experiments on motion which paved the way for many physicists in later years, including Sir Isaac Newton who formulated the mathematical laws of motion and universal gravitation. In 1581, when Galileo was in the University of Pisa, he noticed a swinging chandelier, which air currents shifted about to swing in larger and smaller arcs. He used his pulse as a timer and noticed that the chandelier took about the same time to oscillate regardless of how far it swung. He went home and conducted the experiment using several pendulums and concluded that a simple pendulum was isochronous, which meant it swung the same amount of time independent of its amplitude. Later on however, Christiaan Huygens, a Dutch mathematician discovered that this was only approximately true.

Galileo is better known for his experiments on motion. Contrary to the ideas of Aristotle, who believed that heavy bodies possessed a substance called ‘gravity’ and light bodies possessed a substance called ‘levity’ which caused heavier bodies to fall faster to the ground than lighter objects, Galileo said that the rate of acceleration of a falling object was independent of its mass, provided the opposing forces due to friction and drag were minimised. He proved this when he was studying metal spheres of different masses rolling down a groove in an inclined plane. He wanted to measure the distance travelled by the ball as function of time after release.  He demonstrated that for a given angle, they all took the same time to reach the bottom of the plane. This was because they were accelerated by the component of the gravitational force acting along the slope, and being spheres, they had very little friction. Galileo could show that this experiment was equivalent to free fall, but slower and thus easier to observe. Using the inclined plane at small angles made timing much easier as all he was using to time the spheres was his own pulse.

Galileo also carried out a demonstration from the top of the Leaning Tower of Pisa for everyone to see. According to a biography by Galileo's pupil Vincenzo Viviani, in 1589 Galileo had dropped two balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass. Thus he discovered that objects fell at the same acceleration, proving his prediction to be true, while at the same time proving Aristotle's theory of gravity (which states that objects fall at speed relative to their mass) false. Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. He derived the correct kinematical law for the distance travelled during a uniform acceleration starting from rest, stating that it would be proportional to the square of the time elapsed. 

There were others who had suggested this theory earlier and Galileo had expressed the time-squared law using geometrical constructions and mathematically precise words, adhering to the standards of the day. He concluded that objects retained their velocities unless a force, namely friction, acts upon them, refuting the generally accepted Aristotelian hypothesis that objects "naturally" slow down and stop when they run out of force. Galileo also designed an experiment to demonstrate the parabolic path of a projectile in flight, thus contradicting Aristotle’s idea of force running out. He rolled a sphere down a curved track so that it was projected from the end through a series of hoops. He adjusted the positions of the hoops so that the sphere passed through each one, showing directly the parabolic path. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion.

These experiments of Galileo and his theories were not well received by the Catholic Church then who condemned him for "vehement suspicion of heresy". However, his work acted as a platform for several physicists and mathematicians who followed. Sir Isaac Newton said, “If I have seen further it is by standing on ye sholders of Giants.” Galileo’s ideas and experiments might not have been popular with most people during his time but they are now knowingly or unknowingly, an integral part of our daily lives.

This article was originally published in the 'Fight Club' issue of Portsmouth Point magazine in July 2013.

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