What are the three types of friction?

• A. Dynamic friction, static friction, and rolling friction.
• B. Static, kinetic, and rolling.
• C. Static, rolling, and viscous.
• D. Static, kinetic, and sliding.

Answer: (B)

Friction is the resistance to motion between surfaces, and in introductory physics we typically categorize it into three main types: static friction, kinetic (sliding) friction, and rolling friction. Static friction acts when two surfaces are not yet moving relative to each other and adjusts up to a maximum value to prevent motion. As soon as the applied force exceeds that limit, motion begins and the resistance becomes kinetic (sliding) friction, which is usually smaller than the maximum static friction. Rolling friction occurs when an object rolls instead of slides; it is caused by deformation and other resistive effects at the contact and is typically much smaller than static or kinetic friction. This three-part framework—static, kinetic, and rolling—covers the common ways surfaces resist motion in everyday situations, which is why the best choice lists static, kinetic, and rolling. Dynamic friction is another term sometimes used for kinetic friction, but the standard three-category approach is static, kinetic, and rolling.