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Unformatted text preview: Plausibility When you get an answer yourself, or you see someone else’s result, or you see something in the newspaper, don’t just assume that it must be right. If you believe everything that you see in the paper, you’d believe that a man from Mars works in the White House and that astrologers rule the world. Trying to figure out what’s right and wrong in the newspaper is a little harder than what you have to do here. When you get a result describing a physical system, you can’t just believe it, you have to see whether it makes sense, but there are some straight-forward basic tools that let you do it. The simplest is simply to check the dimensions; this is something that you should make a habit — looking at something and saying “That doesn’t make sense!” For example, the position as a function of time is given to be x ( t ) = A + Bt 1 + t , and you instantly see that this is nonsense, because the denominator is 1 + t , adding time ( t ) to the number one. Is 1 + 1 min the same as 1 + 60 sec? It’s meaningless. Or, suppose the position function is stated to be x ( t ) = A + Bt A + Ct , it’s not quite so simple, but whatever the dimensions of A are, they are the same in the...
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- Fall '11