For the invention of this method, Galileo is generally regarded as the world's first scientist. He then combined the results of these experiments with mathematical analysis in a method that was totally new at the time, but is now generally recognized as the way science gets done. Unlike everyone else up to that point, Galileo actually tried to verify his own theories through experimentation and careful observation. It wasn't until the Italian scientist Galileo Galilei (1564–1642) came along that anyone put Aristotle's theories to the test. It was an immensely popular work among academicians and over the centuries it had acquired a certain devotion verging on the religious. The ancient Greek philosopher Aristotle of Stagira (384–322 BCE), included this rule in what was perhaps the first book on mechanics. In the Western world prior to the 16th century, it was generally assumed that the acceleration of a falling body would be proportional to its mass - that is, a 10 kg object was expected to accelerate ten times faster than a 1 kg object. Only an object in free fall will experience a pure acceleration due to gravity. In accordance with the theory I am about to present, the two objects landed on the lunar surface simultaneously (or nearly so). Astronaut David Scott released a rock hammer and a falcon feather at the same time during the Apollo 15 lunar mission in 1971. (In the olden days in Great Britain, a coin called a guinea was used and so this demonstration is sometimes called the "guinea and feather".) A more dramatic demonstration was done on the surface of the moon - which is as close to a true vacuum as humans are likely to experience any time soon. Under such conditions, a coin and a feather can be shown to accelerate at the same rate. It is possible to do this in the classroom with a vacuum pump and a sealed column of air. The only way to do that is to drop the objects in a vacuum. If only somehow we could eliminate air resistance altogether. We're getting closer to the essence of this problem. Now when the paper and pencil are released, it should be obvious that their accelerations are identical (or at least more similar than before). Repeat the experiment, but before you begin, wad the piece of paper up into the tightest ball possible.If we could somehow reduce this drag we'd have a real experiment. Something else is getting in the way here - and that thing is air resistance (also known as aerodynamic drag). The acceleration of the pencil is noticeably greater than the acceleration of the piece of paper, which flutters and drifts about on its way down. Hold them at the same height above a level surface and drop them simultaneously. Free fall occurs whenever an object is acted upon by gravity alone. When this happens, an object may be falling, but it is not in free fall. Light objects accelerate more slowly than heavy objects only when forces other than gravity are also at work. The two quantities are independent of one another. "What are the factors that affect the acceleration due to gravity?" Mass does not affect the acceleration due to gravity in any measurable way. Although this may seem true on first inspection, it doesn't answer my original question. That is, heavy objects fall fast and light objects fall slow. What are the factors that affect this acceleration due to gravity? If you were to ask this of a typical person, they would most likely say "weight" by which they actually mean "mass" (more on this later). If it wasn't, it would have continued moving away from you in a straight line. Even the object tossed straight up is falling - and it begins falling the minute it leaves your hand. Your object was accelerating because gravity was pulling it down. In each of these examples the acceleration was the result of gravity. Since acceleration is the rate of change of velocity with time and velocity is a vector quantity, this change in direction is also considered acceleration. This time throw it horizontally and notice how its horizontal velocity gradually becomes more and more vertical. Pick up your battered object and launch it one last time. But acceleration is more than just changing speed.Decreasing speed is also considered acceleration. On the way up its speed will decrease until it stops and reverses direction. Pick up this same object and toss it vertically into the air. But acceleration is more than just increasing speed.The longer it falls the faster it travels. When you release it from your hand, its speed is zero. Pick something up with your hand and drop it.
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