Physics
Acoustic Impedance
Quick fact
At a boundary between air and water, only about 0.1% of sound energy is transmitted; the rest is reflected back. This is why underwater sounds are nearly silent to someone above the surface.
Why this is interesting
Why can you hear a whale from miles away underwater, but a loud concert outside feels muffled when you plunge into a pool? The answer lies in a hidden property of every material: its acoustic impedance.