Teacher Talk: What’s up with Fireworks?

November 2, 2017 9:00 am

This week’s Teacher Talk comes from our headteacher Gemma in the Science Department. With Bonfire Night just around the corner, Gemma wanted to teach us all a little about what’s really going on in fireworks…

What exactly are fireworks?

 

WHIZZ! WOOSH! BANG! It’s all we’re hearing at the moment, as it’s the time of year that we have fireworks to celebrate many different occasions. But have you ever wondered how fireworks actually work? How do they explode into different colours? And who thought it would be a good idea to have fireworks anyway?

Well it is widely believed that the essence of fireworks was discovered, by accident, by a Chinese cook over 2000 years ago. The black powder, which is now known as gunpowder, was stuffed inside bamboo tubes and thrown onto the fire. The gasses produced would build up in pressure and then explode. Hey presto! We have the first firecracker.

It wasn’t until the 13th century that gunpowder was first recorded in Europe by an English scholar and monk called Roger Bacon who investigated the composition of the chemicals in gunpowder.  The most famous account of the use of gunpowder comes from the 17th Century, of course it was the ‘Gunpowder Plot’! This plot to kill King James I of England is the entire reason we have Bonfire night and fireworks on the 5th November.

Left: Guy Fawkes arranging barrels of gunpowder under the Houses of Parliament. Right: fireworks celebrating modern day Bonfire Night above Big Ben

So what are in fireworks?

 

The base for any firework will be the part that makes it explode. This is known as Potassium Nitrate. This reacts with sulfur and carbon to form potassium sulphide, nitrogen gas and carbon dioxide. By lighting the fuse on a firework, we add enough energy to kick-start the chemical reaction and BANG! you have the explosion.  But fireworks are not just all about the explosion, they make pretty colours too. These are all due to the metal compounds that are packed inside. So sodium compounds give yellow and orange, copper give green or blue and calcium and strontium give red.

That’s the chemistry, but then there’s the physics… A basic law of physics, the conservation of energy, states that the total chemical energy packed into the firework before it ignites must be the same as the total remaining in it after it explodes, plus the energy released as light, heat, sound and movement. Physics can also explain why fireworks always make symmetrical explosions. Another basic law of physics, the conservation of momentum, states that the momentum of a firework must be the same before and after an explosion, so explosions to the left must be exactly balanced by explosions to then right.

Is it only physics that’s involved?

 

I wouldn’t like to leave out the biology side of fireworks, but what could biology possibly have to do with fireworks?! Well our Science Sparkies will be well aware of the safety procedures in a science lab when handling explosives. It is exactly the same when handling fireworks. Fireworks should be kept in a box with a lid. Instructions should be read using a torch, not a flame. A safe distance should be kept between yourself and the firework and you should never put them in your pockets! Sparklers should be held at arms length and when finished should be placed in a bucket of water or sand. Finally, never return to a firework that has not gone off… it may decide to do just that once you are right next to it!