Mechanical engineering, being one of the fundamental disciplines in Engineering apply the principles of mechanics and energy to the design of machines and devices. Mechanical engineers are involved with the design of structures, operation, and maintenance of mechanical systems. Mechanical engineers design automobiles, trucks, airplanes, and trains for transportation; tractors for food production; interplanetary space vehicles; copying machines, fax machines, staplers, and mechanical pencils used in the office; and lathes, milling machines, grinders, and drill presses used in the manufacture of goods.