When you sip soda through a straw, you are utilizing the
simplest of all suction mechanisms. Sucking the soda up causes
a pressure drop between the bottom of the straw and the top of
the straw. With greater fluid pressure at the bottom than the
top, the soda is pushed up to your mouth.
In its 100-year history, the electric vacuum
cleaner has become an indispensable home appliance for
most people, and it's obvious why. Imagine picking all
this sawdust out of the carpet by
This is the same basic mechanism at work in a vacuum
cleaner, though the execution is a bit more complicated. In
this edition of HowStuffWorks,
we'll look inside a vacuum cleaner to find out how it puts
suction to work when cleaning up the dust and debris in your
house. As we'll see, the standard vacuum cleaner design is
exceedingly simple, but it relies on a host of physical
principles to clean effectively.
It may look like a complicated
machine, but the conventional vacuum cleaner is actually made
up of only six essential components:
- An intake port, which may include a variety of
- An exhaust port
- An electric motor
- A fan
- A porous bag
- A housing that contains all the other components
When you plug the vacuum cleaner in and turn it on, this is
- The electric current operates the motor.
The motor is attached to the fan, which has angled
blades (like an airplane
- As the fan blades turn, they force air forward,
toward the exhaust port (check out How
Airplanes Work to find out what causes this).
- When air particles are driven forward, the
density of particles (and therefore the air
pressure) increases in front of the fan and decreases
behind the fan.
This pressure drop behind the fan is just like the
pressure drop in the straw when you sip from your drink. The
pressure level in the area behind the fan drops below the
pressure level outside the vacuum cleaner (the ambient air
pressure). This creates suction, a partial vacuum,
inside the vacuum cleaner. The ambient air pushes itself into
the vacuum cleaner through the intake port because the air
pressure inside the vacuum cleaner is lower than the pressure
Two upright vacuum cleaner models, one with
the conventional bag system (right), and the other with
the new "cyclone" system
As long as the fan is running and the passageway through
the vacuum cleaner remains open, there is a constant stream
of air moving through the intake port and out the exhaust
port. But how does a flowing stream of air collect the dirt
and debris from your carpet? In the next section, we'll find
out how this works.
Picking Up the Dirt
In the last section, we
saw that the suction created by a vacuum cleaner's rotating
fan creates a flowing stream of air moving through the intake
port and out the exhaust port. This stream of air acts just
like a stream of water. The moving air particles rub against
any loose dust or debris as they move, and if the debris is
light enough and the suction is strong enough, the
friction carries the material through the inside of the
vacuum cleaner. This is the same principle that causes leaves
and other debris to float down a stream. Some vacuum designs
also have rotating brushes at the intake port, which
kick dust and dirt loose from the carpet so it can be picked
up by the air stream.
Upright vacuum cleaners usually have rotating
brushes on the bottom to knock dirt loose from your
carpet. The brushes may be rotated by the vacuum's motor
or simply by the rushing
As the dirt-filled air makes its way to the exhaust port,
it passes through the vacuum-cleaner bag. These bags
are made of porous woven material (typically cloth or paper),
which acts as an air filter. The tiny holes in the bag
are large enough to let air particles pass by, but too small
for most dirt particles to fit through. Thus, when the air
current streams into the bag, all the air moves on through the
material, but the dirt and debris collect in the bag.
The vacuum cleaner bag is simply a filter
that lets air pass through but keeps dirt
You can put the vacuum-cleaner bag anywhere along the path
between the intake tube and the exhaust