Firework science
by Chris Woodford. Last updated: December 27, 2018.
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 lots of 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. Fireworks teach us some interesting physics and chemistry, so let's take a closer look at what they are and how they work!
Photo: A fireworks display at Seattle Seafair. Photo by Douglas G. Morrison courtesy of
US Navy.
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!
Photo: A summer firework display in Swanage, England. A single firework can involve dozens of separate explosions.
The science of fireworks
Science teachers love fireworks because they teach you about chemistry and physics at the same time, in a very dynamic and colorful way!
Chemistry of fireworks
An exploding firework is essentially a number of chemical reactions happening simultaneously or in rapid sequence. When you add some heat, you provide enough activation energy (the energy that kick-starts a chemical reaction) to make solid chemical compounds packed inside the firework combust (burn) with oxygen in the air and convert themselves into other chemicals, releasing smoke and exhaust gases such as carbon dioxide, carbon monoxide, and nitrogen in the process. For example, this is an example of one of the chemical reactions that might happen when the main gunpowder charge burns:
2KNO3 (potassium nitrate) + S (sulfur) + 3C (carbon in charcoal form) → K2S (potassium sulfide) + N2 (nitrogen gas) + 3CO2 (carbon dioxide)
What makes the different colors in fireworks? That's chemistry too! 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: Chemical reactions in the sky: different metal salts make the different colors in firework displays.
Clockwise from top left: blue and green = copper or barium; red = calcium or strontium; yellow and white = sodium.
Physics of fireworks
The solid chemicals packed into the cardboard case don't simply rearrange themselves into other chemicals: some of the chemical energy locked inside them is converted into four other kinds of energy (heat, light, sound, and the kinetic energy of movement). According to a basic law of physics called the conservation of energy (one of the most important and fundamental scientific laws governing how the universe works), the total chemical energy packed into the firework before it ignites must be the same as the total remaining in it after it explodes, plus the energy released as light, heat, sound, and movement.
Physics also explains why a firework shoots into the air. The charge is little more than a missile. As it 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 powder packed into the charge burns, it gives off hot exhaust gases that fire backward. The force of the exhaust gases firing backward is like the blast coming out from a rocket engine and creates an equal and opposite "reaction" force that sends the firework shooting forward up into the air.
If you look at the various firework photos on this page, you'll see another bit of interesting physics going on as well. Notice how fireworks always make symmetrical explosions? If one part of the firework goes left, another part goes to the right. You never see a firework sending all its stars to the left or a bigger series of explosions to the left than to the right: the explosion is always perfectly symmetrical. Why is that? It's because of another basic law of physics called the conservation of momentum: the momentum of a firework (the amount of "stuff moving" in each direction, if you like) must be the same before and after an explosion, so explosions to the left must be exactly balanced by explosions to the right.
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 effects of rockets.
We think of fireworks as entertainment, but the same technology has
more practical uses. 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 brighter
and more visible compounds based on magnesium and they're designed to burn for much longer. Even in an age of satellite navigation and radar,
most ships still carry flares like these as a backup method of signaling 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.
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.
- During the mid 13th century, English monk and pioneering scientist Roger Bacon experiments with the composition and manufacture of gunpowder.
- 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.
