The world is filled with people, vehicles, and other objects that are constantly in motion. After studying the force of gravity in the late 1600s, English scientist Isaac Newton developed three laws of motion that described an object's inertia and friction. His third law was the basis for the well-known phrase "for every action, there is an equal and opposite reaction." Whether you are walking to school, playing a sport, or riding a roller coaster, these laws of motion govern the way we live.