* Acceleration is about change in velocity, not just speed. Velocity includes both speed and direction.
* An object can change direction without changing speed. Imagine a car at a stoplight. When the light turns green, it starts moving forward. But before it starts moving, even though its speed is zero, its velocity is changing (from zero to some positive value). This change in velocity means the car is accelerating.
Examples:
* A ball thrown straight up: At the peak of its trajectory, the ball momentarily stops (speed is zero). However, it's still accelerating due to gravity, which is changing its velocity (direction is changing).
* A car turning a corner at constant speed: While the car maintains a constant speed, its direction is changing constantly. This change in direction means the car is accelerating.
Key takeaway: Acceleration is a measure of the *rate of change* of velocity. Even if speed is zero, a change in direction still signifies acceleration.
