In 1687 AD, an English-born scientist, physicist and mathematician named Sir Isaac Newton, published three Latin-language texts that became known to the world as the Philosophiæ Naturalis Principia Mathematica, which translates to "Mathematical Principles of Natural Philosophy" in English. In these three books he presented his findings concerning how forces may act upon an object as well as how said object may respond. His findings, backed up by a variety of mathematical equations, culminated in three concepts called the First, Second and Third Laws of Motion. His writings have been instrumental in helping scientists and engineers, among others, understand the physics of objects in motion or rest, the nature of force and acceleration, and the way two objects exert force upon one another. While Sir Isaac Newton's Three Laws of Motion have since been improved upon by other scientists, these laws have been widely regarded as the most important contributions to physics.

Newton's First Law of Motion

The First Law of Motion pertains to inertia, and is often referred to as the law of inertia. It states that an object that is at rest will stay at rest, until it is acted upon by some kind of force. In addition, an object that is in motion at a given speed and direction will continue to be in motion with the same speed and direction until it is affected by some kind of force. The law of inertia also treats objects in motion or at rest with the same equivalence, which means that in either case, they are obeying the same laws of inertia. The concept dates back to Galileo Galilei, who originally discovered that some force is needed to affect the motion of an object. Other prior contributions to this concept came from Thomas Hobbes and Rene Descartes.

Newton's Second Law of Motion

The Second Law of Motion states that when a force acts upon an object, it will accelerate in the direction it was pushed. In addition, the more mass the object has, the more force will be required in order to accelerate it. This means that in order for an object to move in a direction, it must be pushed in that direction. Furthermore, pushing a basketball is easier than pushing a boulder, because of its mass. In this book Newton introduced the concept of impulse, which is force that is exerted over a period of time. Impulse is thus referred to in the International System of Units as the "newton second". The Second Law of Motion also included the famous mathematical and physical formula "Force equals mass times acceleration", or F=MxA. This law of motion does not apply, however, to objects moving close to the speed of light, or for subatomic particles.

Newton's Third Law of Motion

The Third Law of Motion says that "every action brings an equal and opposite reaction." This means that whenever one object exerts force upon another object, the second object pushes back with equal force. This is important because it is necessary for propulsion to be possible. Fish, for instance, swim by exerting a force upon water with their tails and the water exerts force back at them. Even in outer space, rockets make use of the Third Law because they expel gases behind them and this exerts an opposite force upon the rocket, propelling it forward.

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