Fireworks

Last updated: August 1, 2009.

It's just as well fireworks were invented in ancient times, because such an outrageous invention surely wouldn't be allowed in our risk-averse society today. Just imagine if fireworks didn't exist and someone suddenly suggested the idea of allowing people to fire explosives into the air! Fortunately, that's not the case and we can still enjoy the dazzling magic of these psychedelic aerial displays every time we feel like a joyous outdoor celebration. Let's take a closer look at what fireworks are and how they work!

Photo: Left: A Fourth July fireworks display in front of the Washington Monument. Photo by Robert K. Hamilton courtesy of Defense Imagery. Right: A summer firework display in Swanage, England.

What are fireworks?

A firework is essentially a missile designed to explode in a very controlled way with bangs and bursts of brightly colored light. The word "firework" comes from the Greek word pyrotechnics, which means, very appropriately, "fire art" or "fire skill"; there's certainly no shortage of art and skill in modern firework displays!

Fireworks are essentially explosives packed into hollow cardboard tubes, with a fuse protruding from the bottom and a stick poking out of the end to make them shoot in a straight line. A firework is a bit like a space rocket in that it's made up of several separate stages, with the fuse running all the way through them. As the fuse burns from the bottom upward, it sets fire to each stage in turn, causing a series of explosions that can make a single firework explode in several different ways.

Photo: A single firework can give rise to dozens of separate explosions.

Chemical reactions in fireworks

The first stage is usually made up of tightly packed, coarse explosive powder designed to blast the firework high into the air and safely away from spectactors. Traditionally, gunpowder used in fireworks was made of potassium nitrate (also called saltpeter) mixed with either sulfur and charcoal; more modern fireworks use a variety of other chemicals instead. In this initial phase, the firework is nothing more than a missile. As the first stage burns, the firework is powered by action-and-reaction (also known as Newton's third law of motion) in exactly the same way as a space rocket or jet engine: when the gunpowder burns, it gives off hot exhaust gas that fires backward. The force of the exhaust gas firing backward creates an equal and opposite reaction force that sends the firework shooting forward through the air.

The second stage of a firework has more loosely packed, finer explosive material. As the fuse burns upward, it sets fire to this stage too. Depending on how the stage is made and packed, it either creates the final, colorful explosion there and then or it shoots off a number of firecrackers (mini fireworks) in different directions, causing multiple explosions a few seconds later. You'll have noticed how fireworks always make symmetrical explosions: if one part of the firework goes left, another part goes to the right. That's because of a law of physics called the conservation of momentum: 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 the right.

Fireworks get their color from metal compounds (also known as metal salts) packed inside. You probably know that if you burn metals in a hot flame (such as a Bunsen burner in a school laboratory), they glow with very intense colors— that's exactly what's happening in fireworks. Different metal compounds give different colors. Sodium compounds give yellow and orange, for example, copper and barium salts give green or blue, and calcium or strontium make red.

Photo: Different metal salts make different colors in firework displays. From left to right: blue and green = copper or barium; yellow and white = sodium; red = calcium or strontium.

Types of fireworks

Surprise and variety are the key to any good firework display: if all the fireworks were exactly the same, people would quickly get bored. Although all fireworks essentially work the same way—combining the power of a missile with the glory of burning metallic compounds—there are lots of different types. The ones we've talked about so far are called rockets or skyrockets and produce the most spectacular displays high in the air. Catherine wheels and pinwheels work closer to the ground. They have a number of small fireworks mounted around the edge of a wooden or cardboard disk and make it spin around as they fire off. Roman candles blow out a series of small fiery explosions from a cylinder every so often. Firecrackers are fireworks designed to produce sound rather than light and they're often incorporated into the upper stages of rockets.

We think of fireworks as entertainment, but the same technology has more practical uses. Signalling flares used by military forces and at sea work in almost exactly the same way, though instead of using metallic compounds made from elements such as sodium, they use brightly burning magnesium. Even in an age of satellite navigation and radar, ships still carry flares like these as a backup method of signalling distress.

Photo: Fireworks began as a military technology and they're still used by the armed forces today. Here, sailors onboard the aircraft carrier USS Ronald Reagan are enjoying a July 4 firework display as they sail through the Western Pacific and Indian Ocean. Photo by Jennifer S. Kimball courtesy of US Navy and Defense Imagery.

A brief history of fireworks

Who invented fireworks? Here's our quick history lesson!

• Chinese people believed to have made explosive rockets in the 6th century CE during the Sung dynasty (960–1279CE).
• Arabian world acquires rocket technology from the Chinese around 7th century.
• Rockets similar to fireworks are used during an invasion of China by Mongolian forces in 1279.
• The Mongols introduce firework technology to Europe and it spreads during the Middle Ages. Fireworks are produced in Italy around 1540 and spread to England, France, and other European countries the following century.
• November 5, 1605: Guy Fawkes (1570–1606) attempts to blow up the English houses of parliament with gunpowder buried in the cellar, giving rise to the popular British custom of huge public firework displays on November 5 each year.
• The custom of using fireworks for elaborate celebrations gains popularity in Europe in the 17th century. Prompted by the need to produce ever more spectacular displays, firework manufacturers introduce new chemicals and more sophisticated ways of packaging them.
• Fireworks become popular in the United States during the 19th century, initially as a way of celebrating Independence Day on July 4th.
• 20th century: American scientists Robert Hutchings Goddard swaps the solid fuel in fireworks for a liquid fuel system, pioneering modern space rocket technology that ultimately lands men on the Moon in 1969.