What exactly is "Thunder"?

By: Anjanette Swift

What actually is thunder?

Have you ever been sitting in your house and you see the clouds get dark and is then followed by rain and then before you know it you see that flash of light and we automatically know one thing: it;s a thunderstorm. We've all been on our fair share of thunder storms. And we automatically know it's a thunder storm because during its duration, the sky will repeatedly light and then is followed by a loud and audible " rumbling" noise. But what exactly is that rumbling noise we call thunder and how is it caused?
Thunder completely dependent on lightning so in order to describe what thunder is, we must first talk about lightning. When we see lightning strike, what actually are witnessing the lightning connect from the clouds to the ground, but wee also are witnessing a second strike from the ground back up to the clouds, following the previous path of the strike that came from the clouds. The lightning strike heats up the air surrounding it to 27,000 degrees celsius (which is over five times hotter than the surface of the sun) and this happens at very high speeds. Because this happens so fast, the heated air particles in the strike path don't have enough time to expand, the heated air is compressed and the pressure is 100 times greater than the normal atmospheric pressure. The pressure is far to great and the compressed air explodes, sending a shock wave of compressed air particles in every direction. This explosion causes the loud rumbling noise that we know as thunder.
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Thunder sounds come in a variety. Whenever you hear the thunder that is a loud CRACK, that sound comes directly from the lightning strike. However, the most common thunder noise is the low rumbling that sounds similar to a stomach growl from a starving giant. This noise comes from the the sound waves of the particle explosion echoing off objects such as buildings, cars, trees, and even bodies of people crazy enough to be outside during a thunderstorm.

On another not, the reason thunder ALWAYS happens after lightning and never at the same time as the lightning is because light travels faster than sound. The common myth of "if you count how many seconds between the lightning and the sound of thunder, that's the number of miles the thunderstorm is away from you" derives from that knowledge, in a way. However this myth is inaccurate. It actually takes about 5 seconds for thunder to travel one mile. So if you counted the seconds between the strike of lightning and the thunder and then divided that number by 5, then that would tell you approximately how far the storm was away.


Here are some activities to try that apply to the wonder of thunder:)

1) You and a friend test out the speed of sound! Have you and your friend stand a far distance apart while still being able to see each other. Have one person clap once. When the other person hears the clap, that person should raise their hand. Then keep moving back until you can barely see the person (but can still see them enough to know that they have raised their hand). Have the person that clapped, time how long it takes for the other person to hear and record the data. This will show the speed of sound.

2) During the next thunder storm, after you see a flash of lightning, count the seconds between the flash and the thunder rumble. Then divide that number by five and log it. Then, watch the weather channel and see if that number correlates with where the thunderstorm is on the weather channel.