Freshman physics revisited.Freshman physics courses cover the whole scope of physics, described in textbooks of obscene mass. It is safe to say that none of us ever fully understand physics after that experience, and must take many more courses to make sense of it. After a while we are awarded Ph.D.s, but we still can't say we understand it all, and certainly never will.After that grueling education, it is interesting to return to our freshman physics book to see what we missed back then. Of course those courses could not reveal all the secrets of the universe, and necessarily simplified many things. In the process of simplification, much was lost, and some things were actually not quite correct. Educators used to say that the physics curriculm is a series of revelations, each improving and expanding the previous one. Let's look at a few examples. Example 1. Newton's laws are the bedrock of classical mechanics. They, along with his law of gravitation are said to be "universal", applying strictly everywhere and under all circumstances, now, and in the past and future. But even in the context of classical physics, even a freshman with a skeptical bent should realize that this can not prossibly be correct. Can you find the skeletons in this closet? Using only classical, Newtonian physics, show that Newton's gravitational law, and at least one of his three laws, cannot be universally correct. Do not be distracted by relativity or quantum mechanics, stick to classical physics only. Example 2. Freshman physics courses often speak of rigid bodies. These are bodies that maintain their size and shape exactly under any conditions of stress. Formulate an argument proving that perfectly rigid bodies cannot exist. Example 3. Some have proposed that one solution to the problem of radioactive waste is to load it all onto rockets and send it into space to crash into the sun. Use classical mechanics to explore the serious problems inherent in such a plan. Of course there are serious concerns that the launch rockets might fail and crash back to earth. Also there's the concern that we might someday find a use for that waste and want to have it. But that's not what I'm after here.
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