Here's why:
* Speed is a scalar quantity, meaning it only has magnitude (how fast).
* Velocity is a vector quantity, meaning it has both magnitude (how fast) and direction.
For example:
* A car traveling at 60 miles per hour has a speed of 60 mph.
* A car traveling at 60 miles per hour north has a velocity of 60 mph north.
Therefore, when you want to know how fast something is moving and in what direction, you need to use velocity.
