Friction is a force that opposes motion between two contacting surfaces. Static friction acts when a body resists impending motion, and kinetic friction occurs when the body is in motion, usually being less than static friction. Friction arises from nano-scale irregularities on surfaces. It produces heat, leading to damage and wear of machine parts, reducing their lifespan, and wasting energy. Frictional force can be expressed by F = μN, where μ is the coefficient of friction and N is the normal force. To reduce friction, lubrication and surface smoothening are applied. Frictional forces are categorized into rolling, sliding, static, and kinetic friction, all affected by surface texture and applied force.