Velocity is the speed at which an object moves in a specific direction. It's measured in meters per second, minute or hour in a particular direction—like miles per hour going north, kilometers per minute west or meters per second up. Velocity tells us both the speed and direction we are traveling. Acceleration is a change in velocity. It's measured by subtracting the object's starting velocity from the final velocity, divided by the time this change in velocity took. We usually think of acceleration as speeding up, but it can also mean slowing down. We call this negative acceleration or deceleration.

If a car was driving 45 miles per hour northeast, and is now driving 30 miles per hour north,

A
the car’s velocity decelerated.

B
the car’s velocity accelerated.

C
the car’s velocity remained unchanged.

D
the car’s acceleration is 30 miles per hour.