Kinetic friction is __________ friction.

• A. Static friction
• B. Rolling friction
• C. Moving
• D. Dynamic friction

Answer: (C)

Kinetic friction occurs when there is relative motion between the two surfaces in contact. It is the friction that acts as the surfaces slide past one another, opposing that motion. Because there is movement between the surfaces, describing it as "moving friction" fits the idea of friction associated with sliding motion.

Static friction, by contrast, exists only when there is no slipping between surfaces, or just before motion starts. Rolling friction refers to resistance when an object rolls without slipping, which is a different contact scenario. Dynamic friction is another common name for kinetic friction in many texts, since it describes friction during motion, but the term in this item emphasizes the motion aspect with “moving.”