The Galilean Velocity transformation (GVT) is a very useful tool in everyday life. For example, consider a truck passing someone standing on a street corner. The truck is moving at a constant speed of v=40km/h relative to him. The driver reports that there is a car moving ahead of him in the same direction with a constant speed w = 30 km/h. One can therefore conclude on the basis of the GVT without any doubt that the car is moving with a speed ofk=v+w=70km/h relative to the street corner.
This answer may not be so obvious since speed is a ratioof distance travelled to elapsed time. Adding ratios is more complicated
than necessary in this example, however.