Force, Motion, and Friction Flashcards

A 10 kg box is pushed across a floor with a force of 50 N while friction exerts 30 N opposing the motion. What is the net force on the box?

Answer: 20 N forward

Net force equals applied force minus friction: 50 N − 30 N = 20 N in the direction of motion.

Which surface combination would produce the HIGHEST coefficient of friction?

Answer: Rubber on concrete

Rubber on concrete has a very high coefficient of friction due to the soft, grippy nature of rubber and the rough texture of concrete.

A car traveling at 60 mph suddenly brakes. Which force brings the car to a stop?

Answer: Friction between tires and road

The friction force between the tires and the road surface is what decelerates the car to a stop.

If you double the weight of a box sliding across a floor, what happens to the kinetic friction force?

Answer: It doubles

Kinetic friction force equals the coefficient of kinetic friction times the normal force, so doubling the weight (and thus normal force) doubles friction.

A ball rolls along a flat surface and gradually slows to a stop. Which force is responsible?

Answer: Rolling friction

Rolling friction (or rolling resistance) acts against the motion of a rolling object, causing it to decelerate over time.

An object is moving at constant velocity on a surface. What must be true about the forces acting on it?

Answer: Net force is zero

By Newton's first law, constant velocity means no acceleration, which requires the net force to be zero — applied force equals friction.

Which of the following best describes static friction compared to kinetic friction on the same surfaces?

Answer: Static friction is greater than kinetic friction

Static friction is generally greater than kinetic friction because it takes more force to start an object moving than to keep it moving.