The first law of Newton applies to objects that are:

Question

BlackTom AI · Accepted Answer

Newton's first law states that an object with no net external force acting on it maintains its current state of motion — in particular its velocity remains unchanged.

1) Relevant knowledge points and concepts
- Newton's first law (law of inertia): If the net force on an object is zero, the object has zero acceleration.
- Relation between force, mass, and acceleration: ΣF = m a.
- Velocity vs speed: velocity is speed with direction; a change in direction is a change in velocity even if speed stays constant.

2) Step-by-step reasoning
- Start from ΣF = m a. If ΣF = 0, then m a = 0.
- For a nonzero mass m, this implies a = 0 (acceleration is zero).
- Acceleration zero means the velocity vector does not change in magnitude or direction; the object continues with the same velocity.

3) (Intermediate) symbolic steps
- ΣF = m a
- If ΣF = 0 ⇒ m a = 0
- For m ≠ 0 ⇒ a = 0
- a = dv/dt = 0 ⇒ v = constant

4) Why the correct answer is correct
- Option b says “Experience no change in velocity,” which is exactly the statement a = 0 implies: velocity remains constant. Newton’s first law applies to any object (at rest or moving) whose net external force is zero, so its velocity does not change.

5) Why the other options are incorrect
- a (“Only stationary”): Too restrictive. The law also applies to objects already moving at constant velocity, not only stationary ones.
- c (“Moving at constant speed”): Misleading because constant speed does not guarantee constant velocity — circular motion has constant speed but changing direction (nonzero acceleration), so the first law does not apply there.
- d (“Accelerating or decelerating”): Directly opposite; acceleration (change in velocity) occurs when net force is nonzero, so the first law does not describe accelerating objects.

6) Conclusion
- Therefore the correct choice is b. Experience no change in velocity — this matches the provided answer.

The first law of Newton applies to objects that are:单项选择题

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