The minute you see and hear them, you know it is the start of a joyous celebration. Be it a national holiday or a special occasion, there is one tradition that connects us all: fireworks. The loud cracks and booms and the dazzling magnificence of aerial firework displays is truly a treat for the eyes. Beyond the beauty, have you wondered how such a huge explosion creates a display of various shapes and colours in the sky? Or what substance was needed to create such a beautiful explosion? Everything that we see during a fireworks display is physics and chemistry in action.

Originating from China, legend has it that fireworks were accidentally invented by a Chinese cook who happened to discover how to make explosive black powder by mixing together sulphur, charcoal and potassium nitrate or saltpetre (a salt substitute used in meat curing) – three common ingredients found in a kitchen. When the mixture was compressed into a bamboo tube, the mixture exploded!

The charcoal and sulphur act as the fuel and the saltpetre acts as an oxidizer, which is important in creating an explosion.The combustion of this mixture gave rise to what the modern world now identifies as gunpowder. Isn’t it ironic how such a beautiful yet dangerous invention was created by mistake?

This black powder also helps propel the stunning effects like colour that come along with the explosion. No firework display is complete without the array of colours that paint the sky. You may wonder, what makes the various colours of fireworks? Well, that’s chemistry too! The colour ignited comes from different metal compounds that are packaged as salts inside the fireworks. If you have tried heating metals with a flame, like a Bunsen burner from the school science lab, you would know that they burn intensely in bright colours. This is the same reaction that is happening with fireworks!

What are fireworks if not for the glistening greens and ravishing reds? Different metal compounds produce different colours which we see during a fireworks display. Copper salts give green colour whereas strontium or lithium salts give bright red colours (remember the periodic table!). Although producing colours may seem easy, that’s not always the case. Have you realised that you very rarely witness blue fireworks? Fireworks chemists have claimed that blue is the hardest colour to make, as light blues may appear too light whereas deep blues may seem too dark, making it hard to be seen in the night sky. To make the “perfect blue” is a challenge, since blue light has a shorter wavelength.

Now you may think, what about the flashes and sparkles that appear along with these colours? These effects are made by adding magnesium, titanium and aluminium that produce white sparks whereas adding iron gives gold sparks. No good firework is complete without exciting sound effects. To make a boom or a bang, the mixture is kept in a confined place where gas cannot escape. When it burns, pressure begins to build and causes firework explosions. Making a whistle sound is slightly harder than making a boom as this sound is created when there is a small opening for compressed gas to exit. The type of whistle sound depends on the size of opening and velocity of the gas which escapes.

Every action has an equal and opposite reaction (Newton’s third law of motion) – a law that is applicable even for fireworks. Why does a firework shoot into the air and not to the ground? When the explosive black powder burns, it produces exhaust gases that fire backward. Just like a space rocket engine, the backward force created produces an equal and opposite force by propelling the fireworks forwards and up into the sky.

If you look closely, you may realise that fireworks always make symmetrical explosions. They never launch in a way that sends all their sparkles and stars to just one side. The fireworks always launch in a way that, if one part of the firework goes to the right, the other part always goes to the left. Thanks to the law of conservation of momentum, fireworks are aesthetically pleasing to the eye. The law requires the momentum of the firework to be the same before and after the explosion. Therefore, when they explode, both sides of the explosion must be exactly balanced.

Just like Belva Plain’s quote, “danger hides in beauty and beauty in danger” –  fireworks are a  fun treat,  but if mishandled, the explosions and chemicals are so dangerous it can cause extreme burns, or even worse, kill you. The loud explosions of fireworks can also cause distress to pets and stray animals.

So the next time you are admiring fireworks, be safe and considerate and remember that fireworks not only paint the sky with colours, they paint it with science as well !

To view the infographic: The Missile in Disguise – ESTI DOT MY

Lets test your knowledge about fireworks now: Fireworks! – ESTI DOT MY

Note: Author is an undergraduate student from Sunway University studying Bachelors Degree in Biomedicine.