* Acceleration is a change in velocity, not just speed. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.
* Changing direction means changing velocity. Even if a particle's speed remains the same, if its direction of motion changes, its velocity changes, and therefore it accelerates.
Examples:
* Circular motion: A car traveling at a constant speed around a circular track is accelerating. Its speed doesn't change, but its direction is constantly changing, resulting in a centripetal acceleration towards the center of the circle.
* Uniform circular motion: In this special case, the speed is constant, and the acceleration is always directed towards the center of the circle, resulting in a change in the direction of the velocity.
Key takeaway: Acceleration is about changes in velocity, not just speed. A particle can accelerate if its speed is constant, but its direction of motion is changing.
