Rockets and Missiles

The scientific principle on which rocket propulsion is based was first enunciated in 1687 by Sir Isaac Newton. In his monumental work on force and motion, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), Newton laid out three laws of motion. The third of these stated that for every action, there is an equal and opposite reaction. For example, if you push your finger into a balloon filled with water, the water-filled balloon pushes back with an equal force.

The application of Newton's third law to propulsion is illustrated in a variety of marine animals that use the principle as a means of movement. The body of the squid, for example, contains a sac that holds a dark, watery fluid. When the squid finds it necessary to move, it contracts the sac and expels some of the fluid from an opening in the back of its body. In this case, the expulsion of the watery fluid in a backward direction can be thought of as an "action." The equal and opposite reaction that occurs to balance that action is the movement of the squid's body in a forward direction.