Which friction is described when a wheel rolls on a surface with resistance?

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

Answer: (A)

Rolling friction is the resistive force opposing a wheel as it rolls across a surface. Even when the wheel isn’t sliding, the contact area deforms as the wheel presses down and then recovers, and energy is lost as heat through these deformations and micro-slips. This energy loss creates a small opposing force called rolling resistance. It’s typically much smaller than sliding (kinetic) friction, which would occur if the surfaces actually slid past one another. Static friction, by contrast, is what provides the grip to prevent slipping and to start or sustain rolling, while viscous friction would involve resistance from a fluid. So, when a wheel rolls with resistance, the relevant friction is rolling friction.