How Do Fireworks Actually Work?

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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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6 Factors That Determine Whether or Not You Remember Your Dreams

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Within the scientific community, dreams are still something of a mystery. Many experiments have been conducted and many theories have been put forth, but researchers still don’t fully understand why or how we dream. Further complicating matters is the fact that everyone dreams, but some people never remember their subconscious escapades.

However, improvements in brain imaging and recent physiological studies have brought us one step closer to answering the question of why some people remember their dreams more than others. There’s no simple, definitive explanation, “but there are a number of things that correlate,” Dr. Deirdre Leigh Barrett, a psychology professor at Harvard Medical School and author of The Committee of Sleep, tells Mental Floss. Barrett shared a few of the factors that can affect your dream recall.

1. SEX

Women, on average, recall more dreams than men. Researchers aren’t exactly sure why, but Barrett says it could be a biological or hormonal difference. Alternatively, women might be more cognizant of their dreams because they tend to be more interested in dreams in general. However, Barrett notes that differences between men and women in regard to dream recall are “modest” and that there are greater differences within each sex than between the sexes. In other words: There are plenty of women with low dream recall and plenty of men with high dream recall.

2. AGE

As we get older, it often gets harder to recall our dreams. Your ability to remember dreams improves in late childhood and adolescence, and tends to peak in your twenties, Barrett says. After that point, people often experience a gradual drop-off in dream recall. However, there are exceptions, and people sometimes experience the opposite.

3. PERSONALITY

Again, this is by no means a prescriptive rule, but there seems to be a correlation between certain personality traits and high dream recall. "More psychologically-minded people tend to have higher dream recall, and people who are more practical and externally focused tend to have lower recall," Barrett says. In addition, better dream recall has a “mild correlation” with better recall while completing certain memory tasks during waking hours, according to Barrett.

4. AMOUNT OF SLEEP

The amount of sleep one gets on average is one of the most important factors related to dream recall. People dream every 90 minutes during the REM (rapid eye movement) sleep cycle. However, those REM periods get longer throughout the night, meaning that you’re doing the most dreaming toward the morning—generally right before you wake up. If you only sleep four hours instead of eight, you’re only getting about 20 percent of your dream time. For this reason, some people report remembering more of their dreams on the weekend, when they have the chance to catch up on sleep.

5. BRAIN ACTIVITY

Thanks to brain imaging, scientists now have a better idea of which parts of the brain are associated with dreaming. A part of the brain that processes information and emotions is more active in people who remember their dreams more often, according to a 2014 study. This region toward the back of the brain, called the temporo-parietal junction (TPJ), may help people pay more attention to external stimuli. In turn, this may promote something called instrasleep wakefulness.

"This may explain why high dream recallers are more reactive to environmental stimuli, awaken more during sleep, and thus better encode dreams in memory than low dream recallers," Dr. Perrine Ruby told the International Business Times. "Indeed, the sleeping brain is not capable of memorizing new information; it needs to awaken to be able to do that."

Higher activity in the TPJ and another region of the brain called the medial prefrontal cortex (MPFC) might also "promote the mental imagery and/or memory encoding of dreams," researchers wrote in the study's abstract.

More recently, in 2017, researchers discovered that high dream recall is also linked to higher activity toward the front of the brain. The pre-frontal cortex is the part of the brain that deals with abstract thinking, so it makes sense that it has been linked to dream recall and lucid dreaming (being aware that one is dreaming), Barrett says.

6. RESPONSE TO EXTERNAL STIMULI

In a similar vein, people who remember their dreams more frequently also tend to exhibit more brain activity after hearing their name spoken aloud while they’re awake, according to a 2013 study. Upon hearing their names, a group of “high recallers,” who remember their dreams almost every night, experienced a greater decrease in a brain wave called the alpha wave than a group of “low recallers,” who remember their dreams once or twice a month. This decrease in alpha waves is likely preceded by an increase in brain activity upon hearing their names. Essentially, people with greater dream recall tend to experience activity in more regions of their brain in response to sounds. According to Barrett, there may be an evolutionary explanation for this.

“Evolution wants us to get restorative sleep but it also wanted us to wake up to danger and check it out and be able to go back to sleep quickly afterwards,” she says. Think of the all the dangers our prehistoric ancestors had to deal with, and it's clear that this response is important for survival. In essence, high recallers are “probably just a little more aware and watching during their dream, and that helps make it a long-term memory.”

So what can you do to help you remember your dreams? It may sound simple, but before you go to bed, think to yourself, “I’m going to remember my dreams tonight.” The very act of thinking about dreaming can make a big difference.

“You could say that just reading this article is somewhat more likely to make you recall a dream tonight,” Barrett says. “People who are taking a class on dreams or reading a book on dreams—any short-term intervention of paying more attention to them—tends to create a short-term blip in dream recall.”

When you first wake up, don’t do anything except lie in bed and try to recall any dreams you had. If something comes back to you, write it down or use a voice recorder to crystallize your thoughts. Dreams are still in your short-term memory when you wake up, so they’re fragile and easy to forget.

If you don’t remember anything, Barrett says it’s still helpful to assess how you feel when you first awaken. Are you happy, sad, or anxious? “Sometimes if you just stay with whatever emotion or little bit of content you woke up with,” she says, “a dream will come rushing back.”

Why Are Marathons 26.2 Miles Long?

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iStock/ZamoraA

What's the reason behind the cursed distance of a marathon? The mythical explanation is that, around 490 BCE, the courier Pheidippides ran from Marathon to Athens to deliver news that the Greeks had trounced the Persians at the Battle of Marathon. The trouble with that explanation, however, is that Pheidippides would have only covered a distance of approximately 25 miles. So what accounts for the extra 1.2 miles?

When the modern marathon appeared in the late 19th century, the race distance was inconsistent. During the first Olympic games in 1896, runners jogged along Pheidippides’s old route for a distance of 40,000 meters—or 24.85 miles. (That race, by the way, was won by a Greek postal worker.) The next Olympic games saw the distance bumped to a pinch over 25 miles. And while subsequent marathons floated around the 25 mile mark, no standard distance was ever codified.

Then the Olympics came to London. In 1908, the marathon, which stretched between Windsor Castle and White City Stadium in London, lasted 26.2 miles—all for the benefit of England's royal family.

It wasn't supposed to be that way. Like previous races, the original event was supposed to cover a ballpark of 25 miles. The royal family, however, had other plans: They wanted the event to start directly in front of Windsor Castle—as the story goes, the royal children wanted to see the start of the race from the castle nursery. Officials duly agreed and moved the starting line, tacking on an extra mile to the race.

As for the pesky final 0.2? That was the royal family’s fault, too. The finish line was extended an extra 385 yards so the race would end in front of the royal family’s viewing box.

Those extra 1.2 miles proved to be a curse. The race’s leader, an Italian pastry chef named Dorando Pietri, collapsed multiple times while running toward the finish line and had to be helped to his feet. One of the people who came to his aid was a journalist named Arthur Conan Doyle. Afterward, Conan Doyle wrote about Pietri's late-race struggles for the Daily Mail, saying, "Through the doorway crawled a little, exhausted man ... He trotted for a few exhausted yards like a man galvanized into life; then the trot expired into a slow crawl, so slow that the officials could scarcely walk slow enough to keep beside him."

After the London Olympics, the distance of most marathons continued to hover between 24 and 26 miles, but it seems that Conan Doyle's writing may have brought special attention to the distance of 26.2, endowing it with a legendary "breaker-of-men" reputation. Indeed, when the International Amateur Athletic Federation convened to standardize the marathon, they chose the old London distance of 26 miles and 385 yards—or 26.219 miles.

Writing for Reuters, Steven Downes concluded that, "the marathon race may have been as much a Conan Doyle creation as Sherlock Holmes."

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