Friction is the resistance which one body offers to another sliding over it. Additional work is required to overcome this resistance when it occurs in any mechanical system, thus increasing the power consumption and the energy needed. Considerable research and design effort is devoted to eliminating friction from mechanical systems, aircraft, vehicles, and the various forms of water craft.
It has been estimated that over 30% of energy generated is consumed in friction, manifest as the heating of the moving parts. In the particular case of the automobile, some 20% is so thus wasted.