Fear of Physics Read Free Page A

abstraction had been made, the rest was literally straightforward: Galileo argued that objects moving freely, without being subject to any external force, will continue to move “straight and forward”—along a straight line at constant velocity—regardless of their previous motion.

    Galileo arrived at this result by turning to examples in which the medium exerts little effect, such as ice underfoot, to argue that objects will naturally continue at a constant velocity, without slowing down, speeding up, or turning. What Aristotle had claimed was the natural state of motion—approaching a state of rest—is then seen to be merely a complication arising from the existence of an outside medium.
    Why was this observation so important? It removed the distinction between objects that move at a constant velocity and objects that stand still. They are alike because both sets of objects will continue doing what they were doing unless they are acted upon by something. The only distinction between constant velocity and zero velocity is the magnitude of the velocity—zero is just one of an infinite number of possibilities. This observation allowed Galileo to remove what had been the focus of studies of motion—namely, the position of objects—and to shift that focus to how the position was changing, that is, to whether or not the velocity was constant. Once you recognize that a body unaffected by any force will move at a constant velocity, then it is a smaller leap (although one that required Isaac Newton’s intellect to complete) to recognize that the effect of a force will be to change the velocity. The effect of a constant force will not be to change the position of an object by a constant amount, but rather its velocity. Similarly, a force that is changing will be reflected by a velocity whose change itself is changing! That is Newton’s Law. With it, the motion of all objects under the sun can be understood, and the nature of all the forces in nature—those things that are behind all change in the universe—can be probed: Modern physics becomes possible. And none of this would have been arrived at if Galileo had not thrown out the unnecessary details in order to
recognize that what really mattered was velocity, and whether or not it was constant.
     
     
    Unfortunately, in trying to understand things exactly we often miss the important fundamentals and get hung up on side issues. If Galileo and Aristotle seem a little removed, here’s an example that is closer to home. A relative of mine, along with several others—all college-educated individuals, one a high school physics teacher—invested over a million dollars in a project involving the development of a new engine whose only source of fuel was intended to be the Earth’s gravitational field. Driven by dreams of solving the world’s energy crisis, eliminating domestic dependence on foreign oil, and becoming fabulously wealthy, they let themselves be convinced that the machine could be perfected for just a little more money.
    These people were not so naive as to believe you could get something for nothing. They did not think they were investing in a “perpetual motion” machine. They assumed that it was somehow extracting “energy” from the Earth’s gravitational field. The device had so many gears, pulleys, and levers that the investors felt they could neither isolate the actual mechanism driving the machine nor attempt a detailed analysis of its engineering features. In actual demonstrations, once a brake on the machine was removed, the large flywheel began to rotate and appeared to gain speed briefly during the demonstration, and this seemed convincing.
    In spite of the complexity of the machine’s details, when these very details are ignored, the impossibility of the machine becomes manifest. Consider the configuration of the prototype I have
drawn below at the start and the end of one complete cycle (when all the wheels have made one complete