Bathtub science
Show yourself how well sound travels through water.

T ry these simple tests in the tub or swimming pool:

• While the bath water is running, listen to the sound it makes splashing into the tub. When there is enough water to slide under and submerge your ears, do so.
  
  
• With your head above the water, hold two spoons below the surface and clink them together, listening to the sound. Then, put your ears under the water, clink the spoons, and listen.
  
  
• Now give the spoons to a friend. With your head above water, close your eyes and have your friend clink the spoons together. Can you tell what direction the sound is coming from? Then, put your ears under the water, keep your eyes closed, and have your friend clink the spoons again, from a different location. It will be harder to tell where the sound is coming from. Now, ask your friend to clink the spoons underwater somewhere. You'll find that you still can't tell which direction the sound is coming from.

What's going on?

Sound that’s generated underwater stays underwater; very little sound passes from water to air. When your head is out of the water and you listen to a sound made underwater, you don’t hear much. But if you put your head under the water, the sound becomes much louder.

You also feel more of a sound when you’re underwater. Above the surface, the sound waves only vibrate your eardrum (unless the sound is very loud). When your head is submerged, your skull also vibrates with the sound because it is close to the same density and elasticity as water. Below the surface, sound waves pass directly through the water and into your head.

You’re witnessing evidence that water is a good conductor of sound. For starters, sound travels through water five times faster than it travels through air. When a sound is carried to you through the air, you judge the location of its source by comparing when the sound reaches one ear versus the other. But when you’re under water, the sound travels so fast that it reaches both ears at almost the same time. That’s why it was hard to tell where your friend was clinking the underwater spoons.