How Do Fireworks Actually Work?

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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's the Difference Between Cement and Concrete?

Vladimir Kokorin/iStock via Getty Images
Vladimir Kokorin/iStock via Getty Images

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
Cement
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This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

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Why Do You Stop Feeling Tired As Soon As You Climb Into Bed?

tommaso79/iStock via Getty Images
tommaso79/iStock via Getty Images

There are few situations more frustrating: After a day spent nodding off at your desk, on the train, and on your couch, you suddenly can't sleep the moment you crawl into bed. It's not that you aren't tired or have insomnia, necessarily. Like a curse designed just to torture you, the sleeplessness only seems to occur when you're in your own bed at home, a.k.a. the place where you'd prefer to do your sleeping.

This maddening problem isn't in your head. According to TIME, many people have more trouble falling asleep in their own beds than they do elsewhere thanks to a phenomenon called learned or conditioned arousal. Conditioned arousal develops when you inadvertently train your body to associate your bed with being awake. In many cases, this results from doing stimulating activities in bed. For instance: If you like to slip under the covers and spend 40 minutes watching Netflix before closing your eyes, you're teaching your brain that your bed isn't for sleeping. That means the next time your head hits the pillow, your body will respond by preparing for the next episode of Friends instead of releasing the chemicals that help you fall asleep. The same goes for scrolling through apps, eating, and even reading in bed.

Doing things that aren't sleeping in bed isn't the only way to develop conditioned arousal. If there are other factors keeping you up at night—like thoughts about your day, or that cup of coffee you had at 8 p.m.—they can lead to the same result. Your brain starts to associate being in bed with tossing and turning all night, so even if those mental and physical stimulants go away, the muscle memory of being awake in bed remains.

Conditioned arousal is a vicious cycle that can't be broken in one night. The only way to manage it, according to the American Psychological Association (APA), is to minimize behaviors that contribute to poor sleep habits and to reserve your bed for sleeping (though sex is OK, according to the APA).

If you're a nighttime scroller, browse apps in a different room before getting into bed, or skip checking your phone at the end of the day altogether. When you spend more than 20 minutes struggling to fall asleep in bed, get up and move to a different part of the house until you get sleepy again; this will stop your brain from strengthening the association between your bed and feeling restless. The results won't be instant, but by sticking to a new sleep routine, you should eventually train your body to follow healthier patterns.

Of course, combating conditioned arousal alone isn't always effective. In people with conditions like anxiety and insomnia, intrusive thoughts and genetic factors can prevent them from falling asleep even under ideal circumstances. In such cases, the help of a medical professional may be required to sleep more soundly.

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