Which type of friction is involved when an object is in motion?

Kinetic friction is the type of friction that occurs when an object is already in motion. This type arises between the surfaces of two objects that slide past one another. The force of kinetic friction opposes the motion of the sliding object and is typically less than static friction, which must be overcome to initiate motion from rest.

Understanding kinetic friction is essential in several practical applications, including engineering and mechanical designs, as it affects the efficiency and energy consumption of moving parts. It plays a critical role in scenarios like vehicles driving on roads and machinery operating under frictional forces.

Static friction, while critical for preventing motion, only acts on objects at rest. Rolling friction pertains to objects that roll over a surface and is usually less than both static and kinetic friction. Fluid friction involves resistance experienced by objects moving through a fluid, whether it be liquid or gas, and is distinct from the friction experienced by solid surfaces in contact.