Fireworks light up the sky over Washington, D.C. | Photo courtesy of the U.S. Department of the Interior.
Last Saturday, America celebrated the signing of the Declaration of Independence and the birth of our nation. Cities and towns commemorated the special day with parades, concerts, festivals and — above all — fireworks!
Here are a few fun facts about the energy of fireworks, and how they help make the Fourth of July so special:
- Standard aerial fireworks are shells with four main parts:
- a cylindrical paper container with string,
- stars, which are cubes or spheres containing the chemicals needed for the reaction,
- a bursting charge in the shell’s center containing black powder,
- a fuse with a time delay to ensure the shell explodes high in the sky.
There’s also a small cylinder with a lifting charge just below the shell, which is shot out of a tube. When the lifting charge fires, the shell’s fuse is lit and burns as the shell rises in the sky. The fuse then ignites the bursting charge when the shell reaches the right altitude, resulting in an explosion.
- Color combinations are produced in the sky when various metal elements are heated, exciting electrons and releasing excess energy in the form of light. The color you see is determined by the chemicals that burn at different wavelengths of light in the spectrum. Higher energy compounds (e.g. copper chloride) emit colors like violet and blue and lower energy compounds (e.g. strontium chloride) emit colors like orange and red.
- Fireworks are the result of chemical reactions involving a few key components — like a fuel source (often charcoal-based black powder), an oxidizer (compounds like nitrates, chlorates that produce oxygen) and a color-producing chemical mixture. The oxidizer breaks down the chemical bonds in the fuel, releasing energy. Fire (either in the form of a fuse or direct flame) kick-starts the chemical reaction.
- The patterns and shapes of fireworks depend on how the stars are arranged inside the shell. For instance, if the stars are spread out equally in a circle shape inside the shell, you will see a similar design in the night sky.
- Fireworks generate three forms of energy: sound, light and heat. That booming sound you hear after the explosion is from the quick release of energy, which causes the air to expand faster than the speed of sound, causing a shockwave.
