Speed is the rate at which an object changes its position. It is a scalar quantity, which means that it has only magnitude and no direction. Speed is measured in units of distance per unit of time, such as meters per second (m/s) or miles per hour (mph).

Velocity is the rate at which an object changes its position in a given direction. It is a vector quantity, which means that it has both magnitude and direction. Velocity is measured in units of distance per unit of time, such as meters per second in a northward direction (m/s N).

The main difference between speed and velocity is that speed does not specify the direction of motion, while velocity does. For example, if a car is traveling at 50 mph, we know how fast it is going, but we don't know which direction it is headed. If the car is traveling at 50 mph N, we know that it is traveling 50 mph in a northward direction.

Speed and velocity are both important concepts in physics. Speed is used to measure how fast an object is moving, while velocity is used to measure how fast an object is moving in a given direction.