Waves

Drop a pebble in a pond and rings race outward. But a floating leaf on those rings doesn't get carried to shore — it just bobs up and down in place. The wave traveled across the whole pond, yet the water didn't go anywhere.

That's the magic of a wave: it moves energy and a pattern, not the stuff it passes through. The same trick lets a stadium 'wave' sweep around the crowd while every fan stays in their seat.