When the first box vibrates, it sends sound waves (oscillations of air) through the room at 412 Hz. If the second box has the same natural frequency, those waves strike it in just the right rhythm. Each wave pushes at the optimal moment, and the energy stacks up. The box starts to vibrate strongly, without ever being touched. But if you try the same thing with a box tuned to 512 Hz? Nothing. The wave energy arrives out of sync, and the pushes cancel out. The energy disperses before it can build