User:Hadseys/Science Theories

The Principle of Least Action
This theory states that things happen in the way that requires the least amount of effort. For example, a beam of light will travel in a straight line because that is the shortest path between the two points. If you drop a ball, it will travel towards the centre of the Earth. The origins of the theory are unknown, but your everyday experience experience would probably lead you to come up with it if you thought about it for a while. In the 18th century, though, this was a big deal. Some of the greatest names in mathematics, such as Leonard Euler, Pierre de Fermat, Gottfried Leibnitz, and Voltaire were involved in the argument over who came up with the idea first. It was important to make these kinds of statements at the time, because they led to the formation of the equations that describe how things move when acted on by forces. They also led to the concepts of potential and kinetic energy.

Laws of motion
When Isaac Newton sat down and thought about how things move, he worked out three laws that are now so familiar they seem like common sense. First, he said that objects have 'inertia', which is a measure of resistance to changes in their motion. Inertia means that things remain still until you give them a push. Similarly, objects that are moving keep moving unless something stops or pushes on them. Second, the mass of the object determines what effect a particular push will have on the motion - or lack of it. The third law, which is the most well-known, feels somewhat different. It says that every action has an equal and opposite reaction. For instance, if I push you, I feel an equal push in return. This is the principle by which space rockets and jet engines work: when they push out an exhaust gas from the nozzle at the rear, the engines get a push forward. This is why you should be careful when you step off a boat; to move forward you inevitably move the boat backward.

Universal Gravitation theory
This description of one of the fundamental forces of nature is among the greatest achievements in science. Isaac Newton came up with it in 1687 as part of his masterful Principia Mathematica, a three volume description of mathematics. Universal gravitation theory says that there is a mutual attraction between anything that has mass - anything made up of normal matter, that is. That attraction depends on the two masses involved, the distance between them, and a constant known as the gravitational constant. One of the central insights into the theory was that the gravitational force follows an 'inverse-square law'. This means tthe attraction between the two objects diminishes as the square of the distance between them. Newton's formulation of the law was so accurate that it immediately explained the motion of the planets, creating an easy way to predict their movements relative to each other and the Sun. It has also enabled us to send rockets into space. After Einstein came up with the theory of relativity and used it to explain some small anomalies in the planetary orbits, it was realized the Newton's law was not quite the final word on gravity. However, it is almost universally accurate when applied to the gravitational attractions we encounter in everyday life.