User talk:Courtanea

Galileo
Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the classical mechanics developed by Sir Isaac Newton. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a mathematical description of the laws of nature. One of the most famous stories about Galileo is that he dropped balls of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass (excluding the limited effect of air resistance). This was contrary to what Aristotle had taught: that heavy objects fall faster than lighter ones, in direct proportion to weight. Though the story of the tower first appeared in a biography by Galileo's pupil, Vincenzo Viviani, it is no longer generally accepted as true. Moreover, Giambattista Benedetti had reached the same scientific conclusion years before, in 1553. Galileo, however, did perform experiments involving rolling balls down inclined planes, which proved the same thing: falling or rolling objects are accelerated independently of their mass. [Rolling is a slower version of falling, as long as the distribution of mass in the objects is the same.] Although Galileo was the first person to demonstrate this experimentally, he was not, contrary to popular belief, the first to argue that it was true. John Philoponus had argued for this view centuries earlier. Galileo determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time. This law is regarded as a predecessor to the many scientific laws expressed later in mathematical form. He also concluded that objects retain their velocity unless a force—often friction—acts upon them, refuting the accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Here again, John Philoponus had proposed a similar (though erroneous) theory. 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 (as the first law). Dome of the cathedral of Pisa with the "lamp of Galileo" Galileo also noted that a pendulum's swings always take the same amount of time, independent of the amplitude. The story goes that he came to this conclusion by watching the swings of the bronze chandelier in the cathedral of Pisa, using his pulse to time it. While Galileo believed this equality of period to be exact, it is only an approximation appropriate to small amplitudes. It is good enough to regulate a clock, however, as Galileo may have been the first to realize. (See Technology below.) In the early 1600s, Galileo and an assistant tried to measure the speed of light. They stood on different hilltops, each holding a shuttered lantern. Galileo would open his shutter, and, as soon as his assistant saw the flash, he would open his shutter. At a distance of less than a mile, Galileo could detect no delay in the round-trip time greater than when he and the assistant were only a few yards apart. Although he could reach no conclusion on whether light propagated instantaneously, he recognized that the distance between the hilltops was perhaps too short for a good measurement. Galileo is lesser known for but nevertheless credited with being one of the first to understand sound frequency. After scraping a chisel at different speeds, he linked the pitch of sound to the spacing of the chisel's skips (frequency). In his 1632 Dialogue Concerning the Two Chief World Systems, Galileo presented a physical theory to account for tides, based on the Earth's motion. Had it been correct, it would have been a strong argument in support of the idea that the Earth moves. (The original title for the book described it as a dialogue on the tides; the reference to tides was removed by order of the Inquisition.) His theory gave the first insight into the importance of the shapes of ocean basins in the size and timing of tides; he correctly accounted, for instance, for the negligible tides halfway along the Adriatic Sea compared to those at the ends. As a general account of the cause of tides, however, his theory was a failure. Kepler and others correctly associated the Moon with an influence over the tides, based on empirical data. A proper physical theory of the tides, however, was not available until Newton. Galileo also put forward the basic principle of relativity, that the laws of physics are the same in any system that is moving at a constant speed in a straight line, regardless of its particular speed or direction. Hence, there is no absolute motion or absolute rest. This principle provided the basic framework for Newton's laws of motion and is the "infinite speed of light" approximation to Einstein's special theory of relativity.