Which of the following best describes inertia?

• A. A tendency of an object to resist changes in motion
• B. A force that opposes motion between two surfaces
• C. The energy stored by a body due to height
• D. The rate of doing work

Answer: (A)

Inertia is the tendency of an object to resist changes in its motion. This means an object wants to keep moving in the same direction at the same speed or stay at rest unless a net external force causes a change. The statement that best captures this idea is that an object tends to resist changes in its motion. Friction, by contrast, is a force that opposes motion between surfaces, not a property that resists changes in motion itself. Potential energy is energy stored by height, and power is the rate at which work is done, neither of which describe the resistance to changes in motion.