When we look
at the speedometer of a moving vehicle we see its speed. When pilots
go flying they need to know the wind speed and its direction. In other
words they need to know the velocity of the wind.
The graph below shows the speed and velocity of a rocket as it is launched
vertically into the air. Notice that the speed is the magnitude of the
rate at which distance is changing. Velocity, on the other hand, is
the magnitude of the rate at which distance is changing and in what
direction. In this case a positive velocity indicates upward motion
while a negative value indicates a downward motion.