In an inertial reference frame, what occurs when an object is in motion?

When an object is in motion within an inertial reference frame, it can indeed maintain a constant velocity. An inertial reference frame is one where an object either remains at rest or moves at a consistent speed in a straight line unless acted upon by a net external force. This concept is rooted in Newton's first law of motion, often summarized as the principle of inertia, which states that an object will not change its state of motion unless a force causes it to do so.

Hence, if no net external forces are acting on the object, it will continue moving at a uniform velocity. This could mean it is moving at a constant speed in one direction or even being stationary. Therefore, it is entirely accurate to say that in an inertial frame, an object's velocity may be constant, reflecting the foundational principles of classical mechanics.

In contrast, the other choices either imply conditions that do not necessarily reflect the nature of motion in an inertial frame or suggest occurrences that would not arise without external influences.