Which term describes the tendency to resist changes in motion?

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

Answer: (C)

Resistance to changes in motion comes from inertia, a property of matter that makes objects tend to keep doing what they’re already doing. This idea is captured by Newton’s First Law: an object at rest stays at rest, and an object in motion continues moving at the same velocity unless a net external force acts on it. The heavier the object, the greater its inertia, which is why it’s harder to start moving a heavy cart or to stop it once it’s going.

Acceleration describes how quickly velocity changes, but it’s the rate of change itself, not the resistance to change. Momentum is the amount of motion (mass times velocity) and relates to how difficult it is to stop an object, but the term for the resistance to changing motion is inertia. Friction is a force that opposes motion between surfaces, affecting motion, not the inherent resistance to change.