According to Newton's first law, what happens to an object at rest if the net external force is zero?

• A. It moves in a straight line at constant speed
• B. It accelerates
• C. It remains at rest
• D. It disappears

Answer: (C)

Inertia is the tendency of an object to keep doing what it’s already doing unless something else acts on it. If the net external force is zero, there’s no unbalanced push or pull, so the object doesn’t accelerate. For an object that starts at rest, zero acceleration means its velocity stays zero, so it remains at rest.

The other ideas would require some change in motion: moving with constant speed would need the object to already have a nonzero velocity, which isn’t the case here; acceleration would need a net force to cause a change in velocity; disappearing isn’t a consequence of having no net force.