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. 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 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 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. 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. He drew inspiration from many scientists that came before him, most notably Galileo Galilei and Rene Descartes.
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. Collectively known as the Philosophiæ Naturalis Principia Mathematica, where he explained what he called the Three Laws of Motion.
