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Static Electricity
LEARNING TIP
The word “static” means
“not moving.” The term
“static electricity” is used
to describe electric charges
that stay on an object.
There are two types of electricity: static electricity and current
electricity. When the electric charges are in motion, the electricity is
called current electricity. You will look at current electricity in
Chapter 6. When the electric charges are at rest, or not moving, the
electricity is called static electricity.
Static electricity occurs when electric charges build up on an
object. This happens when negative charges are transferred from one
object to another through rubbing, or friction. Examples of static
electricity include the electric charges that build up when clothes
rub against each other in a dryer, when you shuffle your feet across
a carpet, or when you rub your hair or a pet’s fur with a balloon
(Figure 1). The effect of a wool cloth being rubbed on a balloon is
another example of static electricity. Static electricity can even build
up when gasoline flows through a nozzle or when an airplane travels
through air. Static electricity is also responsible for the flashes of
lightning that you see during a thunderstorm.
Figure 1
When a cat’s fur is rubbed with a balloon, the balloon becomes negatively charged and
the cat’s fur becomes positively charged. The attraction between the balloon and the
cat's fur results from static electricity.
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Static electricity can be used to do work. For example, a photocopier
uses static electricity to make copies. A Van de Graaf generator uses
static electricity to produce some “hair-raising” effects (Figure 2).
Figure 2
Touching a Van de Graaf
generator makes your
hair stick out because
each strand of hair has
the same charge and is
repelled by the other
strands.
Where Do Static Electric
Charges Go?
You probably noticed that a charged balloon does not
stick to the wall for very long. What happens to the
electric charges? Usually they go into the air, which is
what happens to the charges on a balloon. When a
balloon loses its static electric charges, it becomes
neutral again and no longer sticks to the wall.
When static electricity leaves an object, it is called
an electric discharge. An electric discharge can be slow
and quiet, like when static electricity escapes into the
air from a balloon. An electric discharge can also be
sudden and can occur with a tiny spark, a shock, or a
crackling sound, like when you pull a sock from a
sweater. A lightning bolt is a dramatic example of an
electric discharge (Figure 3). What words would you
use to describe lightning?
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Figure 3
Lightning can be very unpredictable. It is
created when air currents, moving within large
thunderclouds, push tiny ice crystals and water
droplets past each other and transfer charges.
When the static electricity is discharged, it
produces both the flash of light and the sound
of thunder.
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LEARNING TIP
Connect what you are
reading to your daily life.
Think about how you could
prevent static electricity in
your home.
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Preventing Static Electricity
Everyone knows that lightning is dangerous. However, even small
static charges can cause problems. For example, a static electric
charge can damage the electronics of a computer. The charge is
created as you touch your fingers to the keyboard and mouse. If you
hold your hands close to a computer monitor, you may feel and hear
the static electricity.
There are several ways to discharge charged objects. One way is to
transfer the charges to the ground with a wire or a metal rod. This is
called grounding. It is one of the simplest ways to discharge static
electricity because Earth easily accepts electric charges.
People who work on sensitive
electronic equipment wear a
metal strip around one wrist.
The metal strip is attached by
a wire to a grounding system.
This ensures that any charges
are conducted, or transferred,
to the ground.
You can discharge the static electricity in a computer, and avoid
zapping the computer components, by placing the keyboard or
computer on an anti-static mat, by touching the metal case of the
computer or the metal legs of a chair,
or by touching the floor and
grounding
yourself before
working.
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Tall buildings and some houses have grounding devices called
lightning rods to protect them from lightning. A lightning rod is
a metal rod that is attached to the highest part of a building. The
rod is connected to a heavy copper wire that runs along the side of
the building to a metal plate buried in the ground. If lightning
strikes the building, the lightning rod directs the electric charge
safely to the ground.
To prevent static electricity from building up in a clothes
dryer, you can toss a fabric softener sheet in the dryer. The
sheet will roll around with the clothes and lessen the buildup
of electric charges.
CHECK YOUR UNDERSTANDING
1. Draw a diagram to show how static electricity can affect an object.
Draw a second diagram to show one way that the static electricity on
the object can be reduced.
2. Look at the following list and think about what you have learned:
lightning bolt, grounding, discharge, zap, electric charge, attract,
lightning rod, static electricity
Find pairs of words that have some connection. Write the pairs in
your notebook, and explain the connections. For example, “An
electrician can use a metal strip around one wrist as a grounding
device to help control static electricity.”
3. Describe two ways that you can control a static discharge in your home.
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