Here's why:

* Speed is a scalar quantity, meaning it only has magnitude (how fast something is moving). It doesn't care about direction.

* Velocity is a vector quantity, meaning it has both magnitude and direction.

Think of it this way:

* You're driving a car at 60 mph (speed). This tells you how fast you're going.

* You're driving a car at 60 mph due east (velocity). This tells you how fast you're going *and* in what direction.

If you're moving in a straight line without changing direction, the direction part of velocity becomes irrelevant, and the magnitude of both speed and velocity will be the same.

Example:

* A car traveling at 50 mph due north has a speed of 50 mph and a velocity of 50 mph north.

However, if you change direction, even if your speed remains constant, your velocity changes.

Example:

* A car traveling at 50 mph due north then turns and travels 50 mph due west. The speed remains 50 mph, but the velocity has changed because the direction has changed.