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It can strike without warning,
at any moment.
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You may be walking across a soft carpet
and reaching for the door knob
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when suddenly "zap!"
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To understand static electricity,
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we first need to know a bit
about the nature of matter.
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All matter is made up of atoms
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that consist of three
smaller types of particles:
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negatively charged electrons,
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positively charged protons,
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and neutral neutrons.
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Normally, the electrons and protons
in an atom balance out,
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which is why most matter you come across
is electrically neutral.
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But electrons are tiny
and almost insignificant in mass,
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and rubbing or friction can give
loosely bound electrons
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enough energy to leave their atoms
and attach to others,
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migrating between different surfaces.
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When this happens,
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the first object is left
with more protons than electrons
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and becomes positively charged,
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while the one with more electrons
accumulates a negative charge.
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This situation is called
a charge imbalance,
-
or net charge separation.
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But nature tends towards balance,
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so when one of these newly charged bodies
comes into contact with another material,
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the mobile electrons
will take the first chance they get
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to go where they're most needed,
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either jumping off the negatively
charged object,
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or jumping onto
the positively charged one
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in an attempt to restore
the neutral charge equilibrium.
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And this quick movement of electrons,
called static discharge,
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is what we recognize as that sudden spark.
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This process doesn't happen
with just any objects.
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Otherwise you'd be getting
zapped all the time.
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Conductors like metals and salt water
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tend to have loosely
bound outer electrons,
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which can easily flow between molecules.
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On the other hand, insulators
like plastics, rubber and glass
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have tightly bound electrons
that won't readily jump to other atoms.
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Static build-up is most likely to occur
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when one of the materials involved
is an insulator.
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When you walk across a rug,
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electrons from you body
will rub off onto it,
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while the rug's insulating wool
will resist losing its own electrons.
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Although your body and the rug
together are still electrically neutral,
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there is now a charge polarization
between the two.
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And when you reach to touch the door knob,
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zap!
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The metal door knob's loosely
bound electrons hop to you hand
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to replace the electrons
your body has lost.
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When it happens in your bedroom,
it's a minor neusance.
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But in the great outdoors,
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static electricity can be a terrifying,
destructive force of nature.
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In certain conditions,
charge separation will occur in clouds.
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We don't know exactly how this happens.
-
It may have to do with the circulation
of water droplets
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and ice particles within them.
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Regardless, the charge
imbalance is neutralized
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by being released towards another body,
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such as a building,
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the Earth,
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or another cloud in a giant spark
that we know as lightning.
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And just as your fingers can be zapped
over and over in the same spot,
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you better believe that lightning
can strike the same place more than once.