Tendency to resist any change in motion.

• A. Inertia
• B. Mass
• C. Momentum
• D. Energy

Answer: (A)

Inertia is the tendency to resist any change in motion. This means an object at rest will stay at rest and a moving object will keep moving in the same direction and at the same speed unless a net external force acts on it. The amount of inertia depends on mass—the more mass an object has, the more it resists changes in its motion. Momentum and energy relate to motion, but they describe the motion itself or the ability to do work, not the resistance to changing that motion. So this statement points to inertia as the best description, with mass explaining why some objects resist changes more than others.