Physics - P3 - Changing Speed
Direction is important when considering the motion of 2 objects moving near each other.
2 cyclists move towards each other at speeds of 4m/s. The 1st cyclist sees the other cyclist moving towards him. He appears to be moving towards him at a speed of 8m/s - this is the relative speed.
2 cyclists are moving in the same direction. The cyclist at the front appears to be moving away from the other cyclist at a relative speed of 2m/s, increasing the gap between them.