If you take a minute now to visit www.howstuffworks.com, you will be prepared the next time a small child asks you how the vacuum works.  This site gives a clear, and very detailed description of a vacuum’s mechanics.

When you plug the vacuum cleaner in and turn it on, this is what happens:

1. The electric current operates the airplane propeller).
2. As the fan blades turn, they force air forward, toward the exhaust port (check out How Airplanes Work to find out what causes this).
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. But how does a flowing stream of air collect the dirt and debris from your carpet? The key principle is friction.