* Acceleration is a change in velocity. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.
* Constant speed doesn't mean constant velocity. An object can have constant speed but still change its direction. This change in direction means a change in velocity, which means acceleration.
Examples:
* A car traveling at a constant 50 mph around a circular track is accelerating. Even though the car's speed is constant, its direction is constantly changing, resulting in centripetal acceleration.
* A ball thrown straight up into the air is accelerating while it's going up and while it's coming down. Its speed decreases as it goes up, and increases as it comes down. This change in speed means acceleration.
In summary:
An object can be accelerating even if its speed is constant, as long as its direction is changing.
