One of the most important scientists in history was Sir Isaac Newtown (1642-1727). Newton's contributions to mathematics, astronomy, and gravitation paved the way for modern science. Newtonian physics, now known as classical mechanics, describes the motion of bodies under force. Newton's three laws of motion were revolutionary in how human beings understand the universe.
Much of Newtonian physics found its origin in the landmark Principia, which was first published in 1687. Building on work done by Kepler and Galileo, Newton laid out his three laws. The First Law states: "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." In other words, an object in motion remains in motion unless acted upon, known as the Law of Inertia.
Newton's Second Law, the most powerful of the three, states that force is equal to mass multiplied by acceleration, or F=ma. Newton's Third Law may be the most famous, and states that for every action there is an equal and opposite reaction. Newtonian physics was the first attempt to express the relationship between force and momentum through mathematics. By using these three laws, Newton also proved his Law of Universal Gravitation, applying universal forces to both planetary bodies and everyday objects. Contrary to myth, an apple did not fall on Newton's head.