Welcome to You Ask Andy

Albert Stangler, age 12 of New York, N. Y., for his question:

Why do we see lightning before we hear the thunder?

You count the distance of a thunderstorm count the seconds between the flash and the time you hear the roar, allow one mile for each five seconds, and you will have a rough idea of the distance of the stormy explosion. The closer the lightning and the thunder seem to you, the nearer the storm, And silent sheet lightning is generally too far away from us to hear its thunder at all.

In the heart of the storm, the thunder cracks only a tiny fraction of a second after the lighting flashes. A huge storm cloud is teeming with excited electricity and from time to time it must let off its supercharge in a flash to the ground or from cloud to cloud. In less than a second, the scalding electric current rips a waving path through the heavy air of the cloud. The suddenly heated air in this path explodes with a growling crash. News of these two events reaches our eyes as lightning and our ears as thunder.

The news of the lightning reaches us with the speed of light much, much too fast to be told in seconds. News of the thunder must travel with the slower speed of sound. The further away it happens,, the further it lags behind, the longer it takes to reach us.

The speed of sound varies. It depends upon whether it is traveling through solids, liquids or gases and also on whether these substances are hot., warm or cool. Through ordinary air at 0 degrees Centigrade it travels at 1,087 feet a second. It travels through water at about 5,000 feet a second and through steel at 16,500 feet, about three miles., a second. Through ordinary air, it speeds up about ten feet per second with every rising degree of temperature..

Compared with the speed of light, which is about 186,000 miles a second, sound is an old slow poke. This is why you see the plume of smoke from a distant train a few seconds before you hear the whistle. It is also why you see the lightning before you hear the thunder.

If the temperature of the thunderstorm is about 77 degrees Fahrenheit   and it may be much less the sound of the thunder will roll along at about 1,137 feet a second. It will take about five seconds to travel a mile. If the lightning rips through a cloud three miles away from your you will have time to count till 15 seconds before you hear the roar of its thunder„


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