In today’s health-and-safety conscious society, it’s hard to believe we are actually allowed to fire explosives in the air! As well as dazzling us with their colourful and magical aerial displays, fireworks are really interesting from a scientific point of view – both physics and chemistry!
What is a firework?
A firework is a missile containing combustible chemicals, designed to explode in a controlled manner with loud bangs and bursts of brightly coloured light. The word actually evolved from the Greek ‘pyrotechnics’ which means ‘fire art’ or ‘fire skill’. They were first used to ward off evil spirits and then later for celebrations.
Anatomy of a firework
There are lots of different types of firework which all work in different ways. So, let’s look at the simplest kind – a rocket. A rocket has five main parts to it, working from the bottom to the top:
The chemistry of a firework
An exploding firework is simply a number of chemical reactions happening at the same time or in a rapid sequence. Heat provides enough activation energy to make the solid chemical compounds burn with oxygen in the air and release smoke and exhaust gases.
The different colours from fireworks come from the burning of different metal compounds causing chemical reactions on the sky: yellow gold/orange colours come from sodium compounds, green/blue from copper/barium and red from calcium!
The physics of a firework
Energy locked inside the firework is converted into heat, light, sound and kinetic energy. As it burns, a firework gives off hot exhaust gases that fire backwards like the blast out of a rocket engine which creates an equal and opposite reaction that shoots the firework up, like a rocket! Interestingly, fireworks always make symmetrical explosions due to the conservation of momentum.
Fireworks may be entertaining but the same technology has more practical uses for military forces and ships which still carry flares as a backup method of signalling that they need help.
Remember – fireworks are explosive missiles and therefore extremely dangerous – let a responsible adult handle them and stay safe!