Here is another exercise focusing on how the distance, or gap, between two objects changes over time. If a taxi is racing toward you from the north at 3/4 light speed, and another taxi is racing toward you from the south at 1/2 light speed, how quickly from your perspective is each taxi approaching the other?

If one light beam is heading toward you from the right, and another is heading toward you from the left, how quickly from your perspective is each beam approaching the other? (Note: The question is not asking about the speed of light itself, but rather the speed at which the separation between two light beams is decreasing.)