- Length: The SI unit of length is the meter (m). It is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

- Speed: The SI unit of speed is the meter per second (m/s). It is defined as the distance traveled in one second.

- Velocity: The SI unit of velocity is also the meter per second (m/s). It is defined as the rate of change of displacement with respect to time.

Velocity is a vector quantity, which means that it has both magnitude and direction. Speed, on the other hand, is a scalar quantity, which means that it has only magnitude.