Sliding

Sliding is the motion of a body that moves along a surface with continuous contact, such that there is relative motion at the interface between the two surfaces. The state is typically associated with friction and energy dissipation as heat.

This form of motion is distinct from rolling, in which an object rotates about an axis and the contact point with the surface has zero relative velocity at the instant of contact. Rolling generally experiences lower friction than sliding, because there is less resistance to the instantaneous contact.

In physics, friction opposes sliding motion. The kinetic friction force is approximately proportional to the normal force, with magnitude equal to the coefficient of kinetic friction times the normal force. Static friction can be higher and prevents motion until a threshold is exceeded; once sliding begins, the frictional force typically remains roughly constant for a given pair of materials and conditions, though it can vary with speed, temperature, and lubrication. Sliding converts part of the work done on the object into heat and can contribute to wear of surfaces.

Common examples include sliding on ice, sliding a box across a floor, sliding doors, and sliding puzzles such as the 15-puzzle. In engineering and materials science, sliding friction is a key consideration for brakes, clutches, and bearings, with lubricants and surface finishing used to reduce wear. Some systems also exhibit stick-slip dynamics, a phenomenon where motion alternates between sticking and sudden slipping.