Question

when would we say an object is in motion

Answer 1

An object is moving if its position relative to a fixed point is changing. Even things that appear to be at rest move. When we describe the motion of one object with respect to another, we say that the object is moving relative to the other object.
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Answer 2

We would say an object is in motion when:

• Motion is always described by setting a reference point or some relative object.
• With respect to a reference point, or with respect to an observer if the position of an object is changing then that object is said to be moving or in motion.
• An object's position changes with time and is moving at a particular distance from its reference, the object is moving.
• Hence, we can say an object is in motion when one can observe its position changing with time from a fixed reference point or an observer.