The Science Behind Fireworks

Editor's Note: The following article was written by Edina Patch's "Suburban Science" writer Liz Heinecke.

Monday evening at 10 p.m., Richfield residents will have a chance to sit back and enjoy the city's annual display at .

Even the most seasoned fireworks attendee can’t help "ooohing" and "ahhhing" when a sonic thud is followed by a fantastic burst of light, color and falling, twinkling stars.

Have you ever wondered how fireworks work? How do they get so high in the sky? Why doesn’t the whole explosive bundle blow up before it is airborne? How are different colors made? 

Fireworks were invented in China more than one thousand years ago, and were some of the first rockets. At first, they were simple tubes filled with combustible material—like gunpowder—that would explode and burn when lit, pushing the rockets skyward. (Remember Newton’s third law? For every action, there is an equal and opposite reaction.)  Rockets like these are called skyrockets, since they propel themselves into the atmosphere. 

Most fireworks today are filled with small pellets of chemicals that burn in bright colors or sparkle. These chemical pellets are called pyrotechnic stars. The stars are harder to ignite than gunpowder and are made by coating small spheres made of lead or organic material with metal powders, salt, and other materials.

Fireworks can be set off to explode and sparkle on the ground, or they can be shot into the air using a tool called a mortar. Mortars are short pipes set on the ground and filled with gunpowder and can be lit to propel whatever is set on top of them high into the air. 

Aerial fireworks, like the ones you see at , are shot off by mortars and are made up of four parts. A firecracker-like “bursting charge,” sort of like a tiny bomb, is attached to a string fuse and covered with a paper-mache-like sphere. Inside the sphere are a number of pyrotechnic stars.

When the mortar is lit and shoots the firework into the air, the explosion lights the fuse on the firework. Then, just like in the cartoons, the fuse burns down to the bursting charge, causing the whole thing to blow up high in the air. This second explosion ignites the pyrotechnic stars as they fly outward from the center of the shell, making them burn and sparkle brightly. 

The chemical make-up of the pyrotechnic stars determines what color they are and how they’re arranged inside the shell determines the pattern formed in the sky as they burn and fall. More complicated fireworks can be made by putting shells inside of shells or making more than one compartment inside of a shell. 

Sparklers are actually like fireworks, just without the big explosion. A chemical that “sparkles” when it burns (usually a metal compound) is mixed with some other chemicals and used to coat a stick. The compound is mixed together so that it burns slowly, from one end to another, and the sparkles you see are actually the heated metal dust particles glowing, shining and burning.

Happy Fourth of July! Enjoy the fireworks!