Which force would slow a sliding book on a desk?

• A. Normal Force
• B. Gravitational Force
• C. Friction
• D. Tension Force

Answer: (C)

Friction is the force that opposes motion between two surfaces in contact. When a book slides across a desk, friction acts along the surface in the opposite direction to the book’s motion, gradually slowing it down by converting some of its kinetic energy into heat. The gravitational force pulls the book downward, and the normal force from the desk pushes upward; together these vertical forces balance, while friction depends on the normal force and the surface interaction. The friction that matters here is kinetic friction, which exists when the book is already sliding. Tension would only come into play if the book were attached to a string, which isn’t the case in this scenario.