Anthony Difier, age 14, of Hartsville, S.C:

 Does sound travel faster through water

If you enjoy skin diving, you know that you can hear sounds under water. You may not know it, but those underwater sounds travel more than four times faster than they do through the air. And through solid steel, sound travels almost four times faster than it travels through water. The method of travel is the same ‑ by sound waves ‑ but the denser the object the faster sound can travel through it.

The substance through which sound travels is called the medium and sound cannot travel without a medium. There is only silence in a vacuum. The medium through which sound travels must be made of particles such as atoms and molecules. In air, these particles are free and far apart. In water, they cling closer together, which is why water is denser than air. In steel, the particles are locked together in rigid formation.

When someone beats a drum, the sound reaches your ears through the air. The sound begins on the top of the drum which is vibrating up and down from the energy it got from the beating drum stick. Each vibration hits the air above the drum head and compresses a thin layer of molecules closer together. The term for this is condensation. With each vibration the drum head moves up and down. The condensation caused by the up movement is followed by a rarefaction from the down movement. The air expands and rushes in to fill the space left by the descending drum head.

The vibrations go on at a great rate, many times a second. The sound is carried from the area in waves which fan out in all directions. The layer of air next to the vibrating drum causes condensations and rarefactions in the layer of air behind it.

In this way, the sound waves are carried on and on until they reach your ears. They are carried by particles of air, As one particle is sent flying, it crashes into another which crashes into another.

But the gaseous particles of the air are very far apart and one must travel a relatively great distance before it collides with another. In water, the particles are much closer together and they can hand on their sound energy without traveling any great distance, Sound travels through ordinary air at 1,100 feet a second, It travels through water at a speed of 4,700 feet a second. It travels though the much denser medium of steel at 16,400 feet a second,

Perhaps it is easier to remember these speeds in miles. The sound of thunder travels through the air about one mile in five seconds. The sound of a porpoise giggling under water travels a little less than a mile in a second. The sound from a bang on a solid steel bar rips along faster than three miles a second. And all sound travels faster as the temperature rises,