It can strike without warning,
at any moment.

You may be walking across a soft carpet
and reaching for the door knob

when suddenly...zap!

To understand static electricity,

we first need to know a bit
about the nature of matter.

All matter is made up of atoms

that consist of three 
types of smaller particles:

negatively charged electrons,

positively charged protons,

and neutral neutrons.

Normally, the electrons and protons
in an atom balance out,

which is why most matter you come across
is electrically neutral.

But electrons are tiny 
and almost insignificant in mass,

and rubbing or friction can give
loosely bound electrons

enough energy to leave their atoms
and attach to others,

migrating between different surfaces.

When this happens,

the first object is left 
with more protons than electrons

and becomes positively charged,

while the one with more electrons
accumulates a negative charge.

This situation is called
a charge imbalance,

or net charge separation.

But nature tends towards balance,

so when one of these newly charged bodies
comes into contact with another material,

the mobile electrons 
will take the first chance they get

to go where they're most needed,

either jumping off the negatively
charged object,

or jumping onto 
the positively charged one

in an attempt to restore 
the neutral charge equilibrium.

And this quick movement of electrons,
called static discharge,

is what we recognize as that sudden spark.

This process doesn't happen 
with just any objects.

Otherwise you'd be getting 
zapped all the time.

Conductors like metals and salt water

tend to have loosely 
bound outer electrons,

which can easily flow between molecules.

On the other hand, insulators 
like plastics, rubber and glass

have tightly bound electrons
that won't readily jump to other atoms.

Static build-up is most likely to occur

when one of the materials involved
is an insulator.

When you walk across a rug,

electrons from your body
will rub off onto it,

while the rug's insulating wool
will resist losing its own electrons.

Although your body and the rug
together are still electrically neutral,

there is now a charge polarization
between the two.

And when you reach to touch the door knob,

zap!

The metal door knob's loosely 
bound electrons hop to your hand

to replace the electrons 
your body has lost.

When it happens in your bedroom,
it's a minor nuisance.

But in the great outdoors,

static electricity can be a terrifying,
destructive force of nature.

In certain conditions,
charge separation will occur in clouds.

We don't know exactly how this happens.

It may have to do with the circulation
of water droplets

and ice particles within them.

Regardless, the charge 
imbalance is neutralized

by being released towards another body,

such as a building,

the Earth,

or another cloud in a giant spark
that we know as lightning.

And just as your fingers can be zapped
over and over in the same spot,

you better believe that lightning 
can strike the same place more than once.