Question

What is the main difference between speed and velocity?

Answer 1

Velocity is a vector quantity, which means that a body's speed and direction are both required to define it. They are different because: Speed is the rate of change of distance with time

but velocity is the rate of change of displacement with time.

Answer 2

The main difference is that speed is a "scalar" quantity ... it only has size.

Velocity is a "vector" quantity ... it has size AND a direction.