Dear Scouter Atom,
There was a big thunderstorm at camp last weekend. The lightning and thunder happened at the same time, and one of my Scouters said that meant the storm was right above us. As the storm died down, she told us how far away the storm had moved every time there was thunder. How did she do that?
3rd Screech Owl Pack
Sounds like that was a huge storm! I hope your tent or shelter kept everyone nice and dry.
Let’s talk about what makes thunder and lightning first, and then we’ll talk about how you can measure how far you are from a storm.
Thunderclouds are made up of thousands of raindrops, hailstones and ice pellets. Warm air pushes positively charged water droplets to the top of the cloud, while cool air draws negatively charged droplets to the bottom.
As the negative charges in the cloud build up, the energy needs somewhere to go. During a thunderstorm, the surface of the Earth also takes on a positive charge. Negative and positive attract, and the negative charge in the cloud is discharged (or released). The energy moves down towards the ground, and we see the current as lightning. Think about the shock you feel when you touch a metal doorknob after rubbing your socked feet across the carpet. The same thing is happening – but on a much larger scale – when lightning strikes.
Thunder is the sound of lightning. Lightning is very hot – hotter than the surface of the sun! As lightning moves through the air, it heats and expands the air very quickly. This expansion causes a shockwave, which creates the sound we know as thunder.
Light travels three hundred million metres per second, or three million kilometres per second. Imagine being able to run 7.5 million laps around a track in one second! On the other hand, sound travels 340 metres per second, or .340 kilometres per second. That is like running (almost) a whole lap around a track in one second. While light travels too fast for us to measure with our eyes, we can use our ears to measure how far sound has travelled. Sound travels one kilometre in approximately three seconds. By counting the time between a lightning strike and the thunder that follows, you can get a good estimate of how far you are from the centre of the storm. If you count six seconds between lightning and thunder, the storm is about two kilometres away.
Try it out:
Next time there are fireworks nearby, watch the spectacle a known distance (at least one kilometre) from the launch pad. When a firework goes off, count the seconds between the flash you see and the boom you hear. Does your calculation work out to the same distance?
Before your next camping trip, make sure you know how to stay safe during a thunderstorm.
Until next time!
Scouter Atom is a Colony Scouter with a passion for STEM adventures. There is no question too small, no question too large – if you have a question, Scouter Atom has an answer. Send your questions to firstname.lastname@example.org.