The standard vacuum cleaner design is exceedingly simple, but it relies on a host of physical principles to clean effectively.  

The Basics
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 cleaning accessories
• 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 what happens:

1. The electric current operates the motor. The motor is attached to the fan, which has angled blades.
2. As the fan blades turn, they force air forward, toward the exhaust port.
3. 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 outside. 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.  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. 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.  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.

You can put the vacuum-cleaner bag anywhere along the path between the intake tube and the exhaust port, as long as the air current flows through it. In upright vacuum cleaners, the bag is typically the last stop on the path: Immediately after it is filtered, the air flows back to the outside. In canister vacuums, the bag may be positioned before the fan, so the air is filtered as soon as it enters the vacuum. Using this basic idea, designers create all sorts of vacuum cleaners, with a wide range of suction capacities.

Suction Power

The power of the vacuum cleaner's suction depends on a number of factors. Suction will be stronger or weaker depending on:

• The power of the fan: To generate strong suction, the motor has to turn at a good speed.
• The blockage of the air passageway: When a great deal of debris builds up in the vacuum bag, the air faces greater resistance on its way out. Each particle of air moves more slowly because of the increased drag. This is why a vacuum cleaner works better when you've just replaced the bag than when you've been vacuuming for a while.
• The size of the opening at the end of the intake port: Since the speed of the vacuum fan is constant, the amount of air passing through the vacuum cleaner per unit of time is also constant. No matter what size you make the intake port, the same number of air particles will have to pass into the vacuum cleaner every second. If you make the port smaller, the individual air particles will have to move much more quickly in order for them all to get through in that amount of time. At the point where the air speed increases, pressure decreases. The drop in pressure translates to a greater suction force at the intake port. Because they create a stronger suction force, narrower vacuum attachments can pick up heavier dirt particles than wider attachments.

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