Here's why:
* Acceleration is the rate of change of velocity. Velocity, in turn, is speed in a specific direction.
* Motionless objects have zero velocity, and since their velocity isn't changing, their acceleration is also zero.
* Objects moving at a constant speed in a straight line have a constant velocity. Since their velocity isn't changing, their acceleration is also zero.
In simpler terms:
* Motionless: Not moving, no change in speed or direction.
* Constant speed in a straight line: Moving, but not changing speed or direction.
Both situations result in no change in velocity, meaning no acceleration.
