Countdown to kaboom! how experts pack fireworks to create the ultimate light show.
The first step in any Fourth of July show is to decide what types of shells, or fireworks, will wow the crowd. Then, workers don protective gear and carefully hand-pack each shell with "black powder." Why such caution? Black powder is an explosive mixture of chemical compounds, or two or more elements that are chemically combined. A spark could detonate this blend of charcoal, sulfur, and the compound potassium nitrate.
Next, the pyrotechnicians pack in pellets called "stars" that will give each firework its color. Each star is made up of compounds that include one of various metals, says Kenneth Klabunde, a chemist at Kansas State University. The structure of the metals' atoms causes them to emit light at high temperatures. "The light given off is characteristic of the metal involved," Klabunde says. Example: Copper-based compounds burn blue. Those with lithium appear red.
When the Fourth of July arrives, the pyrotechnicians will rely on a computer to dazzle spectators. Special software helps the experts to time each explosion perfectly, even matching a single flash or boom with a note in a song. Once the show begins, it's on autopilot, Zambelli says.
STEPS TO A SKY SHOW
1 LIFF OFF
A computer sends an electric current to the fuse, sparking the life charge (see Anatomy of a Firework p.13). The heat of the lit fuse causes chemical atoms in the lift charge's black I powder to rearrange into new compounds, many of which are gases. The gases expand instantly, propelling the shell skyward.
2 RIGHT HEIGHT
The lift charge lights a second fuse that leads to the burst charge. The burst charge is timed to explode at an optimal viewing height: 60 to 300 meters (197 to 984 feet) up.
3 SHOOTING STARS
The burst charge shoots "stars" outward. If the stars were packed into the shell in a pattern, such as a star, the pellets will shoot outward in that shape.
GIVE ME A BREAK
Some fireworks are set off in multistages. The first stage explodes while the other keep traveling skyward. Their burst charges explode in turn as the fuse reaches them. So one shell can create a series of shimmering displays.
ANATOMY OF A FIREWORK
There are two basic types of fireworks. Spherical shells shoot light in all directions. Cylindrical shells are ideal for setting off multi-stage explosions.
(A) FUSE: Once lit, it activates the lift charge and, ultimately, the burst charge.
(B) LIFT CHARGE: An explosive, containing black powder, propels fireworks skyward.
(C) BURST CHARGE: Made of black powder, it explodes the shell in mid air.
(D) STARS: Chemical pellets that produce colors.
(E) PAPER CASE: Layers of papier-mache and string hold fireworks together.
DID YOU KNOW?
* Black powder, the explosive used in fireworks, is thought to have originated in 10th century--China
* Some fireworks contain "whistles," or screaming discharges. These paper tubes wiggle outward when a shell explodes. When hot gases from the exploding shell pass through a tiny hole in tile robe, whistling sounds result.
* According to tile American Pyrotechnics Association, five U.S. states ban all consumer fireworks (such as firecrackers) and many other states prohibit the use of certain types of fireworks. Why might some slates pass laws banning the use of fireworks that are intended for use by consumers?
HISTORY: The Fourth of July is the most popular clay of tile year for fireworks displays. Do research to learn more about Independence Day. Then, write and perform a class play about the crafting and signing of this charter of freedom.
* As a resource for the cross-curricular connection, above, view high-resolution images of the Declaration of Independence at: www.archives.gov/national-archives-experience/charters/declaration.html
* Learn about the science of fireworks at NOVA's Web site: www.pbs.org/wgbh/nova/fireworks/
DIRECTIONS: Fill in the blanks to complete the following sentences.
1.--plan which types of--, or fireworks, to use to create a crowd-pleasing fireworks display.
2.Fireworks contain--,which is an explosive mixture of chemical or two or more elements that are chemically combined.
3. Chemical pellets called--give fireworks their color.
4. There are two basic types of fireworks: shoot light in all directions.--are ideal for setting off multistage explosions.
5.The--propels fireworks off the ground. Then in midair, the explodes and shoots color-producing chemical pellets outward.
1. pyrotechnicians, shells
2. black powder, compounds
4. spherical shells; cylindrical shells
5. lift charge; burst charge
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|Title Annotation:||Fourth of July|
|Date:||May 8, 2006|
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