Which of the following is NOT a listed type of friction?

• A. Kinetic
• B. Static
• C. Rolling
• D. Viscous

Answer: (D)

The main idea is how friction is categorized for everyday problems. In most introductory discussions, friction is described in three common forms: static friction, which prevents motion up to a limit; kinetic (sliding) friction, which opposes motion once surfaces slide past each other; and rolling friction, which resists the rolling of a wheel or cylinder due to deformation and other small losses. Viscous friction, on the other hand, comes from a fluid’s resistance to motion—like air or oil moving around an object. That isn’t a friction between solid surfaces at a contact patch, so it isn’t listed among the standard friction types. Hence, viscous is the one that doesn’t fit with the typical trio of static, kinetic, and rolling friction.