Sunday Science: How fireworks work - WCAX.COM Local Vermont News, Weather and Sports-

Sunday Science: How fireworks work

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As thousands of people each year watch Burlington's annual fireworks extravaganza from the waterfront or their home, out on the barge on the lake, the pyrotechnics at Northstar Fireworks are making the show happen with a lot of coordination and science.

"Most fireworks are a shell, which looks something like this," says Northstar Fireworks General Manager Tom Swenson as he holds a spherical shell.

Those shells have fuses, which are attached to a leader, a tube of black powder connected to the propellant on the bottom. That's the first explosion you'll hear, sending the shell from the mortar into the air. Then, time fuses burn towards the gunpowder in the center and set off another explosion that shatters the shell.

When the firework bursts, the streams of color that you see shooting through the sky are actually balls called stars, burning as they go through the air. A shell is filled with those, which means when it explodes, it sends them in every direction, and that's why, wherever you're standing during a fireworks show, it looks like they're coming at you.

And what you see depends on the chemicals in the stars. Bariums, sodiums, and other metals all bring out different effects.

"I like to explain these stars as Everlasting Gobstoppers. Because you know how they have different layers? These have different layers in them, and so as they burn through, they'll change colors on you," Swenson says.

For the more specialized fireworks, they need other designs.

"These are a different type of star. They're actually for the cross-sets. You've seen the ones that break and then break again, that's what these are right here," he says.

Reporter Cat Viglienzoni: "And so I'm seeing down here, it looks like we have a smiley face right here. Is that how they make the specific patterns that we see in the air sometimes?"

Swenson: "Yep, so instead of a bunch of little stars like this, you'd actually have something that looks like this. So when the burst charge explodes, it actually throws the stars in a pattern, and that's how you get smiley faces."

How high the fireworks go is determined by the size of the shell, about 100 feet for each inch. They're made in China. Swenson says what's in the fireworks hasn't changed much over hundreds of years, but the method of firing them has. Instead of manually lighting them, most larger shows are set off electronically from panels. With the flick of the switch they can fire the shells instantaneously.

"It's also safer because you can be upwards of a couple hundred feet away. Your timing is better because when you need a shell you just fire it.," he says.

And once they're out on the barge, if the science works, it's showtime, setting off a dazzling display to take your breath away.

If you're wondering, after the show, they do an inspection on the barge to make sure there aren't any duds, or shells that didn't go off, and they also check for loose debris.

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