Here's why:

* Velocity is a measure of speed and direction.

* Acceleration is the change in velocity over a period of time.

Formula for acceleration:

Acceleration (a) = (Change in velocity (Δv)) / (Change in time (Δt))

Units of acceleration:

The standard unit for acceleration is meters per second squared (m/s²).

Examples:

* A car speeding up from 0 to 60 mph in 5 seconds is accelerating.

* A ball thrown straight up slows down as it rises, meaning it's decelerating (negative acceleration).

* A satellite orbiting Earth at a constant speed is still accelerating because its direction is constantly changing.