Mechanical engineers design simple devices like doorknobs and fishing reels, and also work on complex systems such as airplanes, automobiles, satellites, and power plants. In fact, mechanical engineers play a role in most of the things that people drive, play with, or live in.
Mechanical engineers are concerned with the principles of motion, energy, and force.
Generally, a machine converts one form of movement into another. It is the responsibility of engineers to design machines whose parts and assemblies function in a safe and reliable, efficient, and predictable fashion. Indeed, the numerous laws and principles developed by scientists are the everyday tools of the mechanical engineer. Anything the engineer does that is related to the motion and dynamics of heat, gas, air, fluids, and solid materials requires the understanding and application of science. Mechanical engineering encompasses many specialties.