i have a somewhat elusive question (for me) about light. when you drop a bouncy ball, after it hits the ground, right before it bounces back up, its velocity is zero. correct? it becomes troubling when the ball is replaced with light. when light is reflected straight back to its source, it cannot stop or even slow down because of the absolute speed of light. how does it accomplish this? i think ive read its massless but that doesn't seem to help me.