The Physics of War by Barry Parker Page A

result of his observations he came to the following conclusions:
Bodies fall with uniform acceleration (as long as the resistance of the medium is neglected).
Objects in motion retain their motion unless some sort of force acts on them.
The law of acceleration: the total distance from rest under acceleration is proportional to time squared.
    His big break with previous ideas was the statement that a force was present only during the acceleration of the projectile. Once the force was taken away, the object no longer accelerated, but it continued at a constant velocity unless acted upon by another force. This was in conflict with Aristotle's idea that a projectile in motion was under a constant force; in other words, it had a “reservoir” of force that was gradually used up. Galileo said this was incorrect.
    Galileo decided that the most logical curve the projectile would undergo as a result of this was a parabola. What is a parabola? The best way to understand it is to think of a cone (see figure). If you slice through it parallel to the base, you'llget a circle, but if you slice through it at an angle, you'll get a parabola (as long as you don't pass through the base).

    A parabola, the second curve from the top.
    Military Compass
    As a result of his work on projectile motion, Galileo developed a “geometric military compass.” It was a takeoff on Tartaglia's device for gunners, but it had many improvements. It gave gunners a new and safer way for aiming their cannons more accurately. Furthermore, it had scales and numbers on it that told them how much gunpowder was needed for cannonballs of various weights and sizes.
    Like Tartaglia, Galileo abhorred war and felt guilty about developing war weapons, but he felt they were necessary. Also, his wages were relatively low, and it was something that paid well. So not only did he develop the gunner's compass; he had over a hundred built and sold, and he made an excellent profit on them. Furthermore, he taught a class to gunners on how to use the new device, and he also wrote a book on it, which he sold.
    Interestingly, with minimal modifications, the same device was eventually used in surveying.
    The Telescope
    Although it isn't exclusively an instrument of war, the telescope is invaluable in relation to it. The first telescope was built by Hans Lippershey of the Netherlands in 1604. Galileo heard of it within a short time, and he set out to build one. He was already familiar with the grinding of lenses, so he was able to construct one quite quickly. He completed his first telescope in 1609, and it was a significant improvement on Lippershey's model; it had a power of about three (in other words, it magnified three times). Soon after he built an improved one of about eight power, and he presented it to the lawmakers of Venice in 1609. They were thoroughly awed and impressed, and they quickly realized that it would be helpful in the event of an attack, particularly from sea. The sail of an enemy ship, for example, could be seen at least two hours before it could be seen with the naked eye, and this would give a tremendous advantage. He was awarded a stipend for building additional telescopes.
    But the military use was of little interest to Galileo; he was more interested in what telescopes would show him above the earth in the night sky. And over the next few years Galileo revolutionized astronomy. He discovered that Jupiter had four tiny moons, and that Venus presented phases like our moon when seen close up. He also noticed that Saturn had a strange ring around it, and he went on to study our moon, noting that it was covered with craters. And even the sun was different than thought: it was not the pure, clear disk that everyone had assumed. It was covered with dark spots—what are now called sunspots. And finally he looked in detail at the Milky Way and found that it was composed of thousands (perhaps millions) of individual stars. Indeed, over a relatively