Which statement describes Newton's first law of motion?

Which statement describes Newton's first law of motion?

• A. Every action has an equal and opposite reaction
• B. Force equals mass x acceleration
• C. An object will not change its motion unless a force acts upon it
• D. Energy is conserved in all processes

Answer: (C)

Inertia is the tendency of objects to resist changes in their motion. Newton's first law says an object will not change its motion unless a net external force acts on it. So, if there’s no net force, a stationary object stays put, and a moving object keeps moving in the same direction at the same speed. Forces like gravity, friction, or pushes are what can change that motion, producing acceleration. That explains everyday observations, like a puck sliding on ice gradually slowing due to friction, or a space probe coasting indefinitely in the absence of opposing forces. This idea is distinct from the other statements: the third law describes action and reaction forces, the second law links force to acceleration, and energy conservation is about how energy behaves, not about motion changing due to forces.

Inertia is the tendency of objects to resist changes in their motion. Newton's first law says an object will not change its motion unless a net external force acts on it. So, if there’s no net force, a stationary object stays put, and a moving object keeps moving in the same direction at the same speed. Forces like gravity, friction, or pushes are what can change that motion, producing acceleration. That explains everyday observations, like a puck sliding on ice gradually slowing due to friction, or a space probe coasting indefinitely in the absence of opposing forces. This idea is distinct from the other statements: the third law describes action and reaction forces, the second law links force to acceleration, and energy conservation is about how energy behaves, not about motion changing due to forces.