Here's why:

* Speed is a measure of how fast an object is moving. It's the distance traveled over a certain amount of time.

* Acceleration is the rate at which an object's speed changes. It's how much the speed increases or decreases over a given period of time.

Important points about acceleration:

* Positive acceleration means the object is speeding up.

* Negative acceleration means the object is slowing down (also called deceleration).

* Zero acceleration means the object is moving at a constant speed.

Examples:

* A car speeding up from 0 km/h to 100 km/h is accelerating.

* A car slowing down from 100 km/h to 0 km/h is decelerating (negative acceleration).

* A plane flying at a constant speed of 800 km/h has zero acceleration.