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You have probably experienced thunderstorms before. They include a lot of rain, strong wind, really loud thunder, and bright strikes of lightning. How do all of those things happen? To understand how a thunderstorm is formed, it is important to know that warm air rises and cool air falls. Thunderstorms form when a section of cold air pushes a section of warm air up, or when a warm temperature on the ground (especially on a hot summer day) heats the air above it. The moisture in the warm air forms a cloud as it rises up and reaches the cooler air. The type of cloud that forms is called a cumulus cloud. Cold air enters the cloud from the sides and starts to move downward, but at the same time, the warm air keeps moving up and the cloud gets bigger and turns into a cumulonimbus cloud. Then, ice crystals form at the top of the cloud and start falling down through the cloud. The ice usually melts and starts to fall from the cloud as rain, or sometimes hail. Soon thunder and lightning start, too. After about 30 minutes, the cold drafts of air moving downwards pull the storm cloud apart and the rain, thunder, and lightning slow down and then stop completely after about an hour.
Thunder & Lightning
All things are made up of matter and matter is made up of tiny pieces called molecules. Sometimes molecules cause objects to have electrical charges. Some things have negative charges and some have positive charges. You may remember from learning about magnets that opposite charges (a positive and a negative) are attracted to each other and like charges (two positives or two negatives) repel, or try to get away from each other. It is the same for electrical charges. When you run across carpet, then touch a doorknob, your hand might get a little shock. That was static electricity, which can also make your hair stand on end, or a balloon stick to the wall. This happens because the positive charges of one object attract the negative charges of the other.
Lightning also happens because of static electrical charges. In a thundercloud, there are lots of positive and negative charges. Most of the positive charges are at the top of the cloud and the negative ones are at the bottom. The ground has a positive charge, so the negative charges in the cloud and the positive charges on the ground are attracted to each other and pull towards each other. (Sometimes charges are attracted to other charges in other parts of the cloud instead of the ground.) When they get close enough, they will meet somewhere between the cloud and the ground and cause a flash of light, called lightning. That bright flash of light that you see, although it lasts less than a second, has a lot of electrical charge! Lightning makes a crooked path, moving away from things that block its way through the sky, like wind or rain. Sometimes charges are also attracted to other electrical charges in other parts of the clouds or else on the ground. The strong electrical charge that is in a bolt of lightning causes a shock that can hurt humans and animals and damage objects like trees and buildings when it strikes.
Thunder is a result of lightning. The lightning super-heats the molecules in the air around it and makes them expand, or move apart from each other. This causes vibrations that are the sounds we hear. Even though the sound of thunder begins with the lightning, we see the lightning before we hear the thunder because it takes longer for sound to travel than for light. So the light reaches our eyes before the sound goes to our ears.
More About Storms
Thunderstorms can be very dangerous because of lightning and strong wind. You should always seek shelter right away if you think a storm is coming; don't wait until it starts raining or you see lightning or hear thunder. Those things mean the storm has already started and it is dangerous to be outside. The best place to be is indoors, but if you cannot be inside a house or building, a car is the next safest place. Severe thunderstorms can easily destroy things because of the pouring rain, lightning, and very strong winds. They can also turn into tornadoes if the conditions are right. Tornadoes are like severe thunderstorms, but even more dangerous because they move very quickly and strike small areas, which means all of the power of the tornado hits in one smaller area instead of being spread out. They easily destroy buildings, trees, cars, and more.
Another type of storm is a hurricane. Hurricanes are formed a little differently than thunderstorms. They usually form over oceans and move towards land, bringing very strong wind, lots of heavy rain, and huge waves that quickly cause flooding. Hurricanes can cause a lot of damage and often destroy towns and cities that are along the coast of an ocean.
Ice storms, blizzards, and gales are other types of storms that are all caused by warm and cool air moving around in the atmosphere.
Molecules - very tiny pieces that all things are made up of. Molecules can have negative or positive charges.
Atmosphere - the layer of air that surrounds the Earth. This is where changes in the weather happen.
Static Electricity - when negative and positive charges build up and then jump toward each other (because opposite charges are attracted). When you run across carpet, then touch a doorknob, your hand might get a little shock. That was static electricity. It can also make your hair stand on end, or a balloon stick to a wall.
Printable Worksheet & PDF
Use this worksheet to help kids visualize what happens when lightning strikes. Remind them that it can strike from the cloud to the ground or an object on the ground, to other clouds, or even other parts of the cloud. Use the plus and minus signs to reinforce that opposite charges attract to form lightning.