The tendency to resist changes in motion is called what?

• A. Friction
• B. Acceleration
• C. Momentum
• D. Inertia

Answer: (D)

Inertia is the tendency of an object to resist changes in its motion. This means an object at rest tends to stay at rest and an object moving at a certain speed and direction tends to keep moving that way unless something else (a force) changes it. Mass plays a big role here—the more mass something has, the more inertia it has, so it’s harder to start moving or to stop once it’s moving.

Friction is a force that opposes motion between surfaces. Acceleration is how quickly velocity changes. Momentum is the amount of motion an object has, equal to mass times velocity. The concept of inertia specifically describes that resistance to change in motion, which is why it’s the best fit for this question.