If you’ve ever watched a fireworks display, I’m sure you’ve noticed that pyrotechnics are powerful. It isn’t easy to produce that much sound, colorful light, and heat, and science explains how it’s done.
That notorious ‘boom’: As energy from a firework is released into the air, it causes the air to expand faster than the speed of sound. The result of this expansion is a sonic boom. Since light travels more quickly than sound, we often see fireworks sooner than we hear them.
The multitudes of color: Fireworks give off certain colors when metal salts are heated. As a metal absorbs energy, its electrons move from their lowest-energy (ground) state to a higher-energy (excited) state. Soon, the electrons begin to decline back to the ground state, and as they move they emit energy in specific quantities and release it as light. The amount of energy released determines which color of light is emitted.
Man-made stars? The aforementioned metal salts are packaged into small clay cubes that are 3-4 cm in diameter, and are made of an oxidizing agent, a reducing agent, a metal salt, and binders. These handmade stars not only emit sound and light effects, but they dictate the appearance of the firework. They lie in cardboard compartment of a firework’s shell until they are ignited.
The key: The combustion of black powder, a combination of 75% potassium nitrate, 15% charcoal, and 10% sulfur, provides the energy needed to send a firework flying through the air. Black powder is classified as a low explosive since it only explodes at the rate of 3 meters per second, but its power comes from trapping heat and gas in the bottom of a firework’s shell until the gas pressure increases to such a capacity that it escapes and blasts the firework into the air. This low explosive part of a firework is timed to react with the high explosive part, or the stars, of a firework at the pinnacle of its flight through the air. This reaction produces the sounds and colors that accompany fireworks. If the reaction’s timing is off, the firework may misfire and explode too late or too early.
The heat source: Oxidizers such as nitrates, chlorates, and perchlorates are present in the black powder and the stars. Reducing agents, like sulfur and carbon, react with the oxygen from oxidizers to create heated, rapidly expanding gases that provide the energy of a firework’s explosion. These reactions also create vast amounts of heat energy, which makes a firework’s explosion even more intense.
The flat firework myth: While the stars of a firework explode in all directions, when viewed from afar fireworks appear to be flat. When something is moving towards us, we usually perceive it as growing larger, and when it is moving away from us, we perceive it as growing smaller. However, combining the bright fireworks with a dark nighttime sky prevents us from deducing the actual size of a firework’s stars.
Additional Facts fireworks:
- The world’s largest single firework was set off at a festival in Japan in 1988. The shell weighed over half a ton and the burst was over a kilometer across.
- A rocket can reach speeds of 150mph, and the shell can reach as high as 200 meters.
- A sparkler burns at a temperature over 15 times the boiling point of water.
- The world record for the most rockets set off all at once was at the Battle of Flowers Parade in Jersey on August 15, 1997 when 39,210 rockets were launched at the push of a button
- 19,000-33,000 dollars: the cost of Disney’s nightly fireworks shows