What is Lightning?

Lightning in Arlington. Photo: Postdlf (CC-BY-SA)

Lightning in Arlington. Photo: Postdlf (CC-BY-SA)

By Wendy Sadler

Fersiwn Cymraeg.

Today’s blog is all about why we get lightning and then you can try an activity related to lightning for yourself at home. First of all take your hands and place them together. Now, while you are pushing them together, rub them forwards and backwards against each other very quickly. What do you notice? That’s right, your hands get hot. This is because of a force called friction. Friction happens when two or more things rub against each and it is a force that can slow things down – or even tear things apart! If you’ve ever seen a hot-air balloon you’ll already know that warm air rises. In a thunder cloud warm air pushes water molecules higher and higher into the sky. As they cool they fall downwards again. This movement of water molecules creates a lot of bumping around inside the cloud and this means there is a lot of friction between the tiny bits of water. All the bumping means that some even smaller particles – called electrons – get knocked off the water particles.

What is lightning?

The bottom of the cloud is negative with electrons – these push the electrons in the earth’s surface away from the cloud so it ends up positively charged.  Image: science made simple (CC-BY-NC)

These little electrons fall to the bottom of the cloud. They carry negative charge so the cloud becomes charged at the bottom. If we think about charges just like little magnets we can help make sense of what happens next.  The ground underneath the cloud has both positive AND negative bits in it – but because the cloud is like one end of a magnet it repels (or pushes away) things that are the same. This means the negative bits of the ground are pushed deeper into the ground leaving the top bit of the earth positive (because it has lost it’s negative bits!).Eventually, this difference between the cloud and the earth gets so big that it needs to equal out somehow, so a huge bolt of electricity (containing electrons) connects the cloud to the earth and we see lightning! If you’re interested in where lightning is happening right now, you can see a live map of lightning strikes here. If you’re interested in the type of electricity we use at home, then you might like our ‘make a circuit’ workshop called ‘MadLab‘ in your school. You can make your own electronic gadget to take home with you. Find out more about the workshop here.

Make your own charged cloud at home…!

You can make a small scale version of what’s happening in a lightning cloud at home using just a balloon and an empty drinks can.

What to do:

Blow the balloon up and rub it against your hair or a jumper (till it is making your hair stick to the balloon!). Now put the can down on it’s side on the floor (a hard floor without carpet is best) and bring the balloon near to the can but without touching them. The can should start to roll towards the balloon. If you’re quick enough you can keep the balloon moving and have a can race across the floor! You can see more details on this experiment from the brilliant Exploratorium site here

What’s happening?

When you rub the balloon, friction makes electrons come off your hair (or the jumper) and stick to the balloon. This makes the balloon negative. When you put it close to the can, it pushes away the negative bits of the can (the electrons) and leaves it with a positive charge – just like the cloud does to the earth. As opposites attract, the can is now attracted to the balloon and the force between them pulls it along. Rubbing a balloon doesn’t quite give us enough electricity to make lightning. Which is probably just as well! Here is a slow motion video of lightning.

Watch closely and you will see the step leaders heading down from the cloud. These are rarely visible and last only a few thousandths of a second. Note that one reaches the ground and this is the path that the much brighter lightning bolt follows.

Lightning facts

  • At any time there are over 2,000 thunderstorms occurring worldwide, each producing over a 100 lightning strikes a second.
  • That’s over 8 million lightning bolts every day.
  • Each lightning flash is about 3 miles long but only about a centimetre wide
  • A lightning strike discharges about 1-10 billion joules of energy and produces a current of 30,000 – 50,000 amps.


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Posted in Activity, Curriculum, Exploring Science, Physics, Primary
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