Karen Keener, age 13, of Winston Salem, North Carolina, for her question:

Can control towers send words faster than sound?

Ordinary sounds poke along at about one mile in five seconds. Besides, they are stopped by solid walls and even through empty air they soon fade away into silence. True, we can use megaphones and amplifiers to make voices louder and carry farther. But the air traffic directors in a control tower must contact planes many miles away and split seconds are vital to safety. Ordinary sound is much too slow and much too weak for this line of duty.

However, there are other forms of energy that travel faster and farther. Control towers use radio beams that travel at the speed of light, 186,000 miles per second. The control room as well as the planes have equipment for both sending and receiving radio signals. The sending instruments translate ordinary spoken sounds in radio signals and broadcast them. The receiving sets trap the radio signals and translate them back into the ordinary sounds of speech. It takes time to talk and listen, but the actual transmission of the radio takes almost no time at all