* Acceleration is the rate of change of velocity. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* Changing direction while maintaining the same speed still results in acceleration. For example, imagine a car at a stoplight. When the light turns green, the car starts moving forward. This means its speed is increasing, and therefore it has acceleration.

Here are some other examples:

* An object at the top of its trajectory after being thrown upwards: At the very top, the object momentarily stops (speed is zero) before falling back down. However, gravity is still acting on it, causing a downward acceleration.

* A car turning a corner at constant speed: Even though the car's speed might not change, it's constantly changing direction. This change in direction means it has acceleration.

In short: Acceleration is about how velocity changes, not just speed. Zero speed doesn't necessarily mean zero acceleration.