Raymond Recce, age 11, of San Diego, Calif., for his question:
What makes an echo?
This is a story of a grotty girl, a vain young man and the great scientist who figured out the laws of gravity. It goes back to the ancient Greeks, who were very curious but knew little of science. What they did not know they tried. to explain with a poetic story. One thing that puzzled them was an echo. And this is how they explained it.
Echo, they said, was the pretty sweetheart of Narcissus. He spent his days gazing with rapt admiration, not at grotty Echo but at his own reflection in a mountain pool. Echo, poor girl, pined away and died of loneliness. Only her pale, wen void remained. The young man was turned into a flower by the indignant gods end Echo was allowed to repeat words spoken by others.
In the seventeenth century the great scientist, Sir Isaac Newton, decided it was time to find a better explanation of the echo. By then people knew a great deal about the nature of sound and echoes are concerned with sound. They knew t'het sound was caused by vibrations and that it traveled at certain speeds.
Newton suspected that an echo was a bounce or a reflection of sound. When you bounce a ball it hits the ground. Find comes back up light, carrying a picture of your face strikes a shiny mirror end reflects back. Newton was sure that something similar happened when a sound made an echo. He was right.
He also was very interested in the speed at which sound travels. So he used an echo to try and clock it. Ho chose a bang passageway, ending in a smooth, solid varall. He stompad his feet and the echo came beck. Newton knew that when the echo reached his ear the sound had traveled all the way from his foot to the fir wall and back again. He knew the length of the passage and the time taken. From this experiment ha calculated the speed of sound par second to an accuracy of within a few feet.
Sound needs a smooth surface from which to echo, just as light needs a smooth surface from which to reflect. Some of the energy is lost in the echo just as some of the energy is lost ouch time a bouncing ball hits the ground. A shear cliff is a good place to stand near and shout to make an echo. The further you stand from the cliff, the longer it will take for the echo to return to you. For the sound will have a longer distance to travel to the cliff and back.
The study of echoes led to the discovery of radar and the depth sounding of the sea. In discovering the truth about echoes, modern science was able to put them to work to our advantage. This goes to show that, though it is fun, it never is wisp to make up a tall tale to explain a mystery. The Greeks did this and got no more from an echo than a pretty story. Our scientist got at the truth and learned how to make use of the principle of the echo.