Here's why:

* Speed refers to how fast an object is moving.

* Direction refers to which way the object is moving.

Acceleration happens when:

* Speed increases: The object is speeding up.

* Speed decreases: The object is slowing down.

* Direction changes: The object is turning, even if its speed remains constant.

Examples:

* A car accelerating from a stop sign.

* A ball rolling down a hill.

* A car turning a corner at a constant speed.

Let me know if you have any other questions!