Laws Of Nature
The founder of modern science, Isaac Newton, thougt that nature behaved in an orderly fashion and the rules of that order could be learned. Preceding Newton were astronomers who measured the angles at which they observed heavenly bodies and the times at which they appeared at these angles. Algebra and geometry were already ancient history in Newton's time. Newton added calculus. Since these mathematical disciplines corresponded neatly to observations, Newton assumed that mathematics was part of nature, and only needed to be discovered. In reality, mathematics was invented, not discovered. The mathematics was made to conform with observation. Therefore it seemed as if nature behaved in obedience to mathematics. In our own time, we have better instruments and more precise measurements. It turns out that the orbits of planets are not perfect ellipses. The position of the earth depends not on the sun alone, but also on the relative positions of the rest of the solar system. In any case, mathematics is not what drives the planets. Newton provided a set of laws of motion. One of these states that for every action there is an equal and opposite reaction. If I am skating on ice, at a moment when I am not moving, I pitch a ball. An accomplice records this event on movie film. By that means we can analyze the motions. The ball moves forward rapidly, but I also move,  backward. Any still from the film shows that the ratio of the distance I moved and the distance the ball moved is constant. Now multiply the mass of the ball by the speed of the ball, and multiply my mass by my speed. The products are equal. During the act of pitching, I exert a force. At any instant, the force felt by the ball is equal to the force felt by me. That is what is meant by equality of action and reaction. The matching of the products of mass times speed is also referred to as equality of action and reaction. The engine that launches a space vehicle is called a reaction motor. The mass of the exhaust times the speed of the exhaust particles is equal to the product of the mass times the speed of the vehicle. Of course this is only imaginary, and it neglects the retarding forces of gravity and air resistance. However, if the space vehicle is in orbit, and we view the event from another vehicle, alongside; we can take a picture that shows that action and reaction are equal. This gives us the illusion that a molecule of exhaust gas is pushing, along with its cohorts, and causing the vehicle to move. A vehicle that is flying away is not pushing anything. The event begins when the fuel is ignited. The chemical reaction that ensues, causes a rapid increase of motion among the gases in the flame. The average gas molecule moves in any direction at the average speed at the temperature of the flame. As many molecules move forward, pushing the vehicle, as move backward and push only themselves. It has been estimated that an exhaust that consists of smaller particles is more effective than an exhaust that consists of larger particles, because the smaller particles gain more speed. It seems plausible. However, the problem is stated too simply. The fuel must engage in a chemical reaction that causes more activity than another reaction would. If two reactions are equal in this respect, the one with the smaller particles will be more effective, pound for pound. If we are to understand the way the world works, we must look for actual causes. 





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