Isaac Newton became famous for his numerous contributions to science and mathematics, most notably his discovery and outlining of the laws of motion in physics and the invention of calculus in mathematics. Newton published various works that became well known among scholars during his lifetime, and his influence continued to remain significant centuries after his death.
The basic laws of motion discovered by Newton centuries ago still hold value for those studying physics. The laws of motion describe the relationship between an object and the forces acting upon it, and how these forces affect the motion of the object. There are three laws of motion described by Newton: an object at rest remains at rest unless acted on by an external force, or an object in motion remains in motion unless acted on by an external force; the motion of an object changes proportionally to the force applied, where force equals mass times acceleration; and when one object acts upon a second object, the second object simultaneously reacts with an equal amount of force in a direction opposite to the first object.
Isaac Newton is also credited with inventing calculus, which he used in calculating the motion of celestial bodies in his studies. However, another mathematician, Leibniz, also published works about calculus during the same time period, so a controversy exists as to which person should be credited with its invention. Since both men used different methods to develop similar ideas regarding calculus, it's generally accepted that both men developed an understanding of calculus independent of each other.