Which statement describes Newton's first law of motion?

Which statement describes Newton's first law of motion?

• A. An object will not change its motion unless a force acts upon it
• B. Every action has an equal and opposite reaction
• C. Force is equal to mass x acceleration
• D. Energy cannot be created or destroyed

Answer: (A)

Motion persists unless a net external force acts on an object. Inertia means an object tends to keep doing what it’s already doing: stay at rest or keep moving in a straight line at constant speed. The statement that an object will not change its motion unless a force acts on it expresses that idea directly—if there’s no net force, velocity stays the same, and only a net force can change how it moves. In real life there are often small forces like friction or air resistance, so motion can seem to change gradually, but the principle describes the baseline: only a force can alter the state of motion. The other ideas describe different physical relationships—how forces relate to acceleration, or how forces come in action–reaction pairs, or how energy behaves—so they don’t capture this specific rule about when motion changes.

Motion persists unless a net external force acts on an object. Inertia means an object tends to keep doing what it’s already doing: stay at rest or keep moving in a straight line at constant speed. The statement that an object will not change its motion unless a force acts on it expresses that idea directly—if there’s no net force, velocity stays the same, and only a net force can change how it moves.

In real life there are often small forces like friction or air resistance, so motion can seem to change gradually, but the principle describes the baseline: only a force can alter the state of motion. The other ideas describe different physical relationships—how forces relate to acceleration, or how forces come in action–reaction pairs, or how energy behaves—so they don’t capture this specific rule about when motion changes.