Depends on what "The Object" is.
It changes over time.
motion
9.8m/s/s
In that case, the speed changes over time.
Change in position over time is velocity ("speed").
If an object's velocity changes over time, it is accelerating.
nothing..
It changes over time.
density changes when the substance changes.
motion
That is equivalent to saying that:* The object moves, or * The object's position changes over time
The rate at which velocity changes over time is known as acceleration. In calculus, acceleration is the derivative of velocity with respect to time.
9.8m/s/s
In that case, the speed changes over time.
the object is moving relative to that point.
Earth surface solwly over time
A record of its positions at different times.