A little less high theory but........
Always been fascinated by the fly hitting the car windscreen "puzzle"
Fly going along at 5 mph - car in opposite direction at 40mph.As the fly strikes the car windscreen it must decelerate from 5 to zero and then to 40 in opposite direction...yes? So when plotting it's speed from 5 in one direction to 40 in the other...a some point it must be zero - or stationary? But the car is moving constantly.