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Everybody loves fireworks --
the lights, the colors,
and, of course, the big boom.
But the history of fireworks
isn't all hugs and celebrations.
Long before epic fireworks displays,
chemists in China invented the key ingredient
that propels those bright lights into the sky.
That invention was what we now call gunpowder.
Our story begins back in ancient China
in the mid-ninth century
where early Chinese alchemists
were trying to create a potion for immortality.
Instead, what they created was a flammable powder
that burned down many of their homes.
They quickly realized that this black powder,
which they called fire medicine,
was precisely the opposite of something
that would make you live forever.
In these early days,
the Chinese hadn't yet figured out
how to make the powder explode;
it was simply very flammable,
and their armies used it
to make flaming arrows
and even a flamethrower.
But once they figured out the right proportions
of ingredients to create a blast,
they began using the powder even more,
creating fireworks to keep evil spirits away
and bombs to defend themselves
against Mongol invaders.
It was these Mongols, most likely,
who spread the invention of gunpowder
across the world.
After fielding Chinese attacks,
they learned how to produce the powder themselves
and brought it with them
on their conquests in Persia and India.
William of Rubruck,
a European ambassador to the Mongols,
was likely responsible for bringing gunpowder
back to Europe around 1254.
From there, engineers and military inventors
created all kinds of destructive weapons.
From bombs to guns to cannons,
gunpowder left its mark on the world
in some pretty terrible ways,
in contrast to the beautiful marks
it can leave in the air.
So, how does black powder propel
fireworks into the sky?
You might have seen old Westerns or cartoons
where a trail of gunpowder is lit
and it leads to a large and obviously explosive barrel.
Once the fire gets to the barrel,
a large boom occurs.
But why doesn't the trail itself explode?
The reason is that burning the powder
releases energy and gases.
While the trail is burning,
these are easily released into the surrounding air.
But when the gunpowder
is contained within the barrel,
the energy and gases cannot easily escape
and build up until
BOOM!
Firework canisters provide
a single, upward-facing outlet
to channel this explosive energy.
The wick ignites the gunpowder
and the energy takes
the easiest exit from the canister,
launching the firework high into the sky.
The flame then makes its way
through the firework's encasing
and the same reaction occurs
high above our heads.
So, while the Chinese alchemists
never found the compound for eternal life,
they did find something
that would go on to shape all of civilization,
something that has caused
many tragic moments in human history,
and yet still gives us hope
when we look up in celebration
at the colorful night sky.
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【TED-Ed】致命的長生不老藥 - 火藥 (The deadly irony of gunpowder - Eric Rosado)

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VoiceTube 發佈於 2014 年 2 月 18 日
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