How Do Fireworks Actually Work?

iStock
iStock

by Sarah Dobbs

Each year, as the Fourth of July approaches, the sound of explosions starts to become a normal part of the evening. Fireworks have existed in one form or another for around 1000 years, and they show no signs of going away anytime soon. But how do they work? Most of us just know to light the fuse and stand back. Let’s take a closer look …

ROCKETS

fireworks over new york city
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Rocket-type fireworks can produce all kinds of different effects when they go off, but the basic structure of an aerial firework stays more or less the same. Each rocket is made up of the following parts: a mortar, fuses, propellant powder, a shell, a bursting charge, and a collection of "stars." The mortar is the outer container, and the fuse is, of course, the piece that you light. When the fuse burns down, the propellant ignites and shoots the firework into the air.

When it’s airborne, a second explosion is triggered inside the shell by a time delay fuse. The bursting charges set off the stars—small, explosive pellets made of fuel and metallic compounds that create the lights in the fireworks display. Different metals create different colors when they ignite: barium goes green, calcium salts go orange, magnesium goes white, copper is blue, lithium turns red, and sodium becomes gold. And the arrangement of the stars will determine the shape of the explosion—so if they’re packed in a heart shape, they should reproduce that heart shape in the sky.

Other effects can also be built in by adding various ingredients; different kinds of fuel can create sound effects, for example, like the whistling or screaming noises some rockets make as they shoot into the sky. Stars can be made up of layers of different metallic compounds, to create multicolored explosions. And in some more complex fireworks, there may be several stages of explosions; in that case, there are generally multiple fuses inside the shell, and as each burns down, a different explosive goes off.

FOUNTAINS

fountain type fireworks
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Of course, not all fireworks are of the shoot-into-the-air-and-go-bang variety. Fountains don’t take off, and generally don’t go bang, either; instead, they stay where they’re placed and give off a cascade of sparks—like a fountain, but with pyrotechnics instead of water.

Usually conical in shape, fountains consist of a paper or plastic tube, with clay plugs at either end. Inside the tube are a couple of different kinds of fuel, plus the metal compounds that create the sparks. When the fuse is lit, the fuel ignites, and sparks are forced out of an aperture in the top of the fountain.

Again, different metals create different colors and effects. Multi-stage effects can be created by bundling multiple tubes together, so that as one finishes another starts, adding different colors or sound effects to the display.

CATHERINE WHEELS

wheel firework
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Catherine wheels are another common type of firework, and again the same kinds of ingredients are used to create a slightly different effect. Named for the unfortunate Saint Catherine, these fireworks are generally fixed to a pole or a mount, so that they can spin as they burn, creating a spiral of sparks.

Bigger Catherine wheels tend to have a plastic disk at their center, with “gerbs” attached around the edge. The gerbs are similar to fountains, in that they’re tubes filled with the mixture of ingredients that create the effects; when lit, the thrust from the explosives makes the wheel turn as they burn. And again, the effect can be made more elaborate with multi-stage effects and different colors; each gerb might be different, so that the wheel changes as each one ignites in turn.

Smaller Catherine wheels might, instead, be made up of a single long, thin tube coiled into shape around a smaller central disk. Again, the thrust of ignition makes the wheel spin.

SPARKLERS

person holding sparkler
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The only firework you should ever hold in your hand once it’s lit is a sparkler—a Fourth of July staple. Unlike most other fireworks, they don’t explode with a bang, but gently fizzle for around a minute, as a ball of sparks makes its way down a metal wire. And they’re pretty simple: basically, the metal wire is dipped into a pyrotechnic compound that’s made up of a metallic fuel, an oxidizer, and a binding material.

The metallic fuel is what creates the sparks; it’s usually aluminum or magnesium, which creates white sparks, but some sparklers may use iron or ferrotitanium for gold sparks instead. The oxidizer, which provides the oxygen to keep the spark going, is generally potassium nitrate. And then a binding material, a kind of flammable starch, keeps the mixture together, and burns away once the sparkler is lit.

Hopefully, none of that has taken away any of the magic of a good fireworks display. If nothing else, you’ll be able to impress your friends by quietly musing “oooh, barium” next time you see a green firework.

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What Happens During a Jeopardy! Commercial Break?

Jeopardy! host Alex Trebek chats with the show's contestants.
Jeopardy! host Alex Trebek chats with the show's contestants.
Getty Images Entertainment

Jennifer Quail:

Typical Break One: First, if there are "pickups" (re-recordings where Alex misspoke or coughed or stuttered, or Johnny mispronounced someone’s name or hometown) to record, they do those. A stagehand brings water bottles for the contestants. The production team who wrangles contestants comes over and gives their pep talk, makes any corrections, like if someone is consistently buzzing early; and keeps you quiet if there are pickups. Alex gets the cards with the "fun facts" (there are about three, one highlighted, but which one he goes for is ultimately up to Alex alone) and when the crew is ready, they come back from commercial to Alex’s chat with the contestants.

Typical Break Two: If there are any pickups from the second half of the Jeopardy! round they do those, the water gets distributed, the production team reminds the contestants how Double Jeopardy! works and that there’s still lots of money out there to win, and Alex comes over to take a picture with the two challengers (the champion will have had their picture taken during their first match.) Then we come back to Double Jeopardy!.

Typical Third Break: This is the big one. There are pickups, water, etc. and they activate the section of the screen where you write your wager. One of the team members brings you a half-sheet of paper ... and you work out what you want to bet. One of your "wranglers" checks it, as does another production team member, to make sure it’s legible and when you’re sure that’s what you want, you lock it in. At that point you can’t change it. They take away the scratch paper and the part of the board where you write your answer is unlocked. Someone will tell you to write either WHO or WHAT in the upper left corner, so you do know at least whether it’s a person or thing. They make sure the "backup card" (a piece of card stock sitting on your podium) is turned to the correct who or what side, just in case your touchscreen fails. If everything’s ready, then as soon as the crew says, they come back and Final Jeopardy! starts.

There are breaks you don’t [even know about, too]. If there is a question about someone’s final answer, they will actually stop tape while the research team checks. Sometimes if something goes really off, like Alex completely misreads a category during the start of a round, they’ll stop and pick it up immediately. Those [are breaks] you’ll never notice because they’ll be completely edited out.

This post originally appeared on Quora. Click here to view.

Why Is There a Leap Day?

Bychykhin_Olexandr/iStock via Getty Images
Bychykhin_Olexandr/iStock via Getty Images

At some point in elementary school, your science teacher probably explained to you that there are 365 days in a year because that’s how long it takes for Earth to complete one full rotation around the sun. What they might not have specified, however, is that it’s not exactly 365 days—it’s actually closer to 365.2421 days.

So, if we want our calendar year to begin right when Earth begins a new rotation around the sun, we have to account for (roughly) an extra quarter of a day each year, or one day every four years. History.com reports that the Egyptians had already been doing this for a while before Europe finally caught on in 46 B.C.E., when Roman dictator Julius Caesar and astronomer Sosigenes put their heads together to come up with what we now call the Julian calendar, which includes 12 months, 365 days, and an additional “leap day” every four years on February 29.

But rounding 0.2421 up to 0.25 each year created an issue, because it didn’t quite add up to a full day every four years—and that tiny discrepancy meant that after 128 years, the calendar year ended up starting a day before Earth had completed its rotation around the sun. By the 14th century, the calendar year was starting a whopping 10 days before Earth finished its orbit.

In 1582, Pope Gregory XIII sought to correct the error by suggesting that we simply skip a leap day every so often. His Gregorian calendar, which we still use today, mandates that we omit the leap day during years evenly divisible by 100 but not by 400. For instance, the year 2000 included a leap day because it’s divisible by 100 and 400; the year 2100, on the other hand, will not include a leap day, since it’s evenly divisible by 100, but not by 400.

Gregory XIII’s correction to Caesar’s overcorrection is itself a bit of an under-correction, so we’ll probably need to reevaluate our leap day protocol again in about 10,000 years.

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