What is the force that must be overcome when one body moves in contact with another body?

• A. Friction
• B. Centrifugal force
• C. Centripetal force
• D. Rolling friction

Answer: (A)

Friction is the resistance that appears when two surfaces are in contact and one moves relative to the other. It acts parallel to the contact surface and opposes motion, so you must overcome it to start or continue movement. This includes static friction that must be exceeded to begin sliding and kinetic friction that resists ongoing sliding. Rolling friction is a related but separate concept that affects rolling motion and is typically smaller than sliding friction. Centrifugal force is a perceived outward force in a rotating frame, and centripetal force is the real inward force needed for circular motion; neither is the resisting contact force described here.