Which of the following statements correctly describes an inertial reference frame?

• A. An inertial reference frame is any frame in which objects always move in circles unless acted upon by a force.
• B. An inertial reference frame is one in which $N^1$'s first law holds true, so a body at rest or in uniform motion remains so unless acted upon by a net external force.
• C. An inertial reference frame is one that is accelerating with respect to the stars.
• D. An inertial reference frame is defined as a frame attached to the surface of the Earth only.

Answer: (B)

Verified step by step guidance

1. Recall the definition of an inertial reference frame: it is a frame of reference in which Newton's first law of motion holds true.
2. Newton's first law states that a body at rest or moving with constant velocity will continue in that state unless acted upon by a net external force.
3. Therefore, in an inertial frame, objects do not spontaneously change their state of motion; they move in straight lines at constant speed or remain at rest unless forces act on them.
4. Frames that are accelerating or rotating (such as those attached to the Earth's surface, which is rotating and accelerating) are generally non-inertial because fictitious forces appear in them.
5. Hence, the correct description of an inertial reference frame is one where Newton's first law holds true, meaning objects maintain their state of rest or uniform motion unless a net external force acts.