What is the term for the force that opposes the motion of two surfaces sliding against each other?

The term that describes the force opposing the motion of two surfaces sliding against each other is kinetic friction. This type of friction acts on objects in motion and is crucial for understanding how surfaces interact when an object slides over another.

When two surfaces are in contact and one is moving relative to the other, kinetic friction arises from the microscopic interactions between the surfaces, which include roughness and other material properties. This frictional force can affect how fast a sliding object slows down, as well as the force required to keep it moving.

Static friction, on the other hand, is the force that prevents two surfaces from starting to slide against each other. Once the surfaces are in motion, kinetic friction takes over. Rolling friction pertains to the resistance that occurs when an object rolls over a surface, which is generally less than sliding friction, while fluid friction involves the resistance encountered by an object moving through a fluid, such as air or water. Each type of friction plays a distinct role in various physical scenarios, but when it comes to sliding motion, kinetic friction is the defining term.