Which term denotes a body's resistance to changes in its motion?

• A. Momentum
• B. Torque
• C. Elasticity
• D. Inertia

Answer: (D)

Inertia is the property of matter that resists changes in motion. An object at rest tends to stay at rest, and an object in motion tends to keep moving at a constant velocity unless a net external force acts. The amount of resistance is determined by mass—heavier objects are harder to speed up or slow down. Momentum, the product of mass and velocity, describes how much motion an object has but is not the resistance itself. Torque relates to turning effects that cause angular acceleration, not linear resistance to motion, and elasticity describes how a material deforms and returns to its shape after a force is removed.