In the last section, we saw that vacuum cleaners pick up dirt by driving a stream of air through an air filter (the bag). 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, because of Bernoulli's principle (see How Airplanes Work to learn about this physical principle). 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.
At the most basic level, this is all there is to a vacuum cleaner. Since the electric vacuum's invention a century ago, many innovative thinkers have expanded and modified this idea to create different sorts of vacuum systems.
So far, we have looked at the most typical types of vacuum cleaners: the upright and canister designs, both of which collect dirt in a porous bag. For most of the history of vacuum cleaners, these have been the most popular designs, but there are many other ways to configure the suction system. We'll look at some of these in the next section.