Sound
Whisper Dishes — Send a Whisper Across the Garden
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Speak softly at the ring of one dish, and someone listening at the ring of the dish across the garden hears you clearly, even though people standing in between may hear almost nothing.
These large dishes are shaped like parabolic reflectors. Sound waves at the focus of one dish spread out, reflect from the curved surface, and travel toward the other dish.
The second dish gathers those waves and reflects them toward its own focus, making the whisper much easier to hear.
The same geometric idea is used in satellite dishes, radio telescopes and directional microphones.
Whisper some numbers into the ring at one dish while someone listens at the ring of the other. How quietly can you speak and still be heard?