# Car Basics – Sir Isaac Newton’s Laws of Motion

Sir Isaac Newton was an English scientist who lived in the 17th and 18th centuries and who made many advances in the fields of mathematics and physics. In 1687 he published a series of three books collectively known as the Philosophiæ Naturalis Principia Mathematica, where he explained what he called the Three Laws of Motion. The First Law of Motion pertained to inertia, the Second Law of Motion explained the principles behind acceleration, and the Third Law of Motion asserted that every force was accompanied by an equal and opposite force. He drew inspiration from many scientists that came before him, most notably Galileo Galilei and Rene Descartes. Isaac Newton’s theories on motion, as well as gravity, are widely regarded by the scientific community as the most important contributions by a single person in the history of the sciences.

First Law of Motion

Newton’s First Law of Motion, which is also referred to as the Law of Inertia, states that an object will not change its speed or direction unless an outside force acts upon it. This means that an object that is not moving, will not move unless something pushes it, and an object that is moving, will need some external force to change its direction or slow it down. Newton’s law of inertia contradicted many existing theories of the time, not the least of which was the belief that an object in motion needed some kind of force to keep it in motion. This law of motion means, for instance, that once a car is put into motion, it will continue to stay in motion, unless another force acts against it. The fact that the car eventually comes to a stop, is not due to the lack of a force, but rather the presence of an opposing force, which is most commonly the force known as friction.

Second Law of Motion Newton’s Second Law of Motion is commonly known as the Law of Acceleration. It says that when an object in motion encounters some kind of force, its direction and speed, also known as its momentum, will change in the direction from which the force is applied. In addition, the change in momentum is inversely proportional to the object’s mass. This means that with a given force, the smaller the object’s mass, the greater the change in momentum, and the greater its mass, the less its momentum will change. For example, a basketball or a car that is rolling downhill will accelerate because of an outside force called gravity. When either object encounters a breeze from the left, Newton’s Second Law of Motion dictates that the breeze is more likely to cause a visible change in the basketball’s speed and direction, than that of the car, because of the difference in mass between the two objects. Furthermore, since the breeze from the left is blowing to the right, the basketball’s change in momentum will cause it to curve toward the right. The car’s change in momentum will be so minor that an observer won’t notice it.

Third Law of Motion Newton’s Third Law of Motion, the law of actions and reactions, states that when a force acts upon an object, an equal and opposite force is applied at the same time. In simpler terms, when something pushes an object, the object pushes back with equal force. This is why when two skaters push against each other, they will both move away from each other, with the heavier person moving less than the lighter person. When a car’s engine starts and makes its wheels spin, its wheels push against the road, and the road applies an opposing force that enables the car to move forward.

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