What is kinetic friction?

• A. Static friction resists motion
• B. Sliding or slipping between two surfaces
• C. Friction that resists motion when rolling
• D. Rolling friction

Answer: (B)

Kinetic friction is the friction force that opposes the motion of two surfaces that are sliding past one another. It comes into play once a relative motion exists, resisting the sliding as the surfaces move against each other. Its strength depends on the normal force and the materials involved, and it’s typically smaller than the maximum static friction that can act before motion starts. Rolling friction, in contrast, is the resistance encountered when an object rolls, not slides, and static friction is what resists motion at the point of contact before any sliding occurs. So the description that matches kinetic friction is the one referring to sliding or slipping between two surfaces.