The velocity of an object moving in a straight line changes at a constant rate when it is experiencing constant acceleration.

Here's why:

* Acceleration is the rate of change of velocity.

* Constant acceleration means the velocity is changing by the same amount over equal time intervals.

For example, if an object is accelerating at 2 m/s², its velocity increases by 2 meters per second every second. This results in a constant rate of change in velocity.