According to Newton's first law, what does the law describe?

• A. An object remains at rest or moves with constant velocity unless acted on by a net external force.
• B. The acceleration of an object is always opposite in direction to the net force acting on it.
• C. For every action force there is an equal and opposite reaction force.
• D. The net force on an object is equal to its mass times its acceleration, $F=ma$.

Answer: (A)

Verified step by step guidance

1. Identify that Newton's first law is also known as the law of inertia, which describes the behavior of objects when no net external force acts on them.
2. Understand that according to this law, an object will either remain at rest or continue to move at a constant velocity in a straight line if no net force is applied.
3. Recognize that this means there is no change in the object's state of motion unless a net external force causes acceleration.
4. Distinguish Newton's first law from the other Newton's laws: the second law relates force to acceleration (\[F = m \times a\]), and the third law states that forces come in equal and opposite pairs.
5. Conclude that the correct description of Newton's first law is: 'An object remains at rest or moves with constant velocity unless acted on by a net external force.'