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Bonfire Night | The Science of Fire

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Remember, remember the 5th of November, gunpowder, treason and plot! We see no reason why the science of fire should ever be forgot!

For this bonfire night, we are looking into the gravity defying properties of water using fire!

Step 1

Pour the water into your container and add the food colouring to colour the water to whatever colour you like, we chose blue.

Step 2

Place the candle in the middle of the water but make sure the wick and wax of your candle stays dry.

Step 3

Get an adult to help you light the candle and make sure the wick is burning for about 20 seconds before moving onto step 4.

Step 4

Place your glass/plastic cup over the candle, this will push all the water away from the candle

Step 5

Wait for a few moments and watch the candle go out and the water rise on the inside of the cup!

The science!

First of all, why does the candle go out?

Fire needs three things to burn; oxygen, fuel and heat. These three things make up the fire triangle which you can see below.

If one of them is taken away, the fire is put out. By putting the cup over the candle, the oxygen is taken away from the fire so it goes out!

But… it doesn’t go out straight away. This is because there is still some oxygen trapped inside the cup but once the fire has used up all the oxygen there is none left so the candle goes out.

So, why does the water in the cup rise after the flame goes out? When the candle is lit, the particles in the air take in some of the heat from the flame and get hotter. When the particles get hotter, they have more energy so move faster and this increases the pressure inside the cup.

After the flame has gone out, the particles cool down and move more slowly and this decreases the pressure in the cup. The pressure outside the cup is then higher than inside the cup so the water is pushed inside the cup until the pressure outside the cup is the same as the pressure inside the cup.

The Science of Fireworks

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We all know the history of Bonfire Night, but do you know the science?

The Explosion

All fireworks are essentially a combustion reaction, like fire, that produces light and heat.

Fireworks tend to have a long fuse that burns slowly so you have time to light the fuse and run away before the big bang! The fuse first reaches a compartment containing gunpowder, it ignites this causing the firework to launch into the night. There is a delayed fuse to ignite the next explosion, this heats the “stars”.

The stars in a firework are individual compartments containing a different composition of chemicals, depending on the desired colour and effect of the firework. The stars may even be arranged inside the shell of the firework so that they burst in a certain formation to form a shape.

The Colours

Firework displays always use a range of striking colours, the variety of colours comes from the use of different chemicals. Elements such as barium, copper and lithium burn with a coloured flame and are chosen for use in fireworks due to the bright colours they produce.

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The Sound

When the chemicals inside the firework’s shell are heated they convert from a solid to a gas. The gas takes up more space than there is available inside the shell so it bursts out creating a loud BANG.

Crackling noises come from fireworks which contain lead. When lead oxide is heated and vapourised, the vapour atoms produce crackling noises.

The whistling sound that you hear when the fireworks shoot up in the air, comes from the firework tube itself, not the chemicals. When the tube is partly empty, it will vibrate the air passing through it, causing a whistle.

How can you write your name with a sparkler?

I’m sure you’ve all held a lit sparkler at some point and twirled it around in the air to see a trail of light lingering in the air for a few seconds. The truth is the light isn’t really still there but your eyes play a trick on your brain to make you think that it is. Image resultOur eyes don’t react as quickly as you might think when our view changes, they usually keep the old view around for a fraction of a second. This is known as visual persistence and it’s what allows us to view a series of still images as movement. The effect is increased in the case of the sparklers due to the very bright light emitted form the sparks contrasting against the dark background. This makes the light appear to last longer.

 

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