More about Dyson's Air Multiplier

The Dyson Air Multiplier uses friction in the air to push out its cool breeze. Around the rim of the circular fan is a little opening from which jets a very thin (1mm or so) air stream at 55mph. That thin stream of air pulls more air into the stream thanks to the aforementioned friction. Physicists call this process entrainment.

At the same time, the air that gets pushed away from the ring towards your beautiful face creates an area of low pressure - not quite a vacuum, but the same effect - in the ring. That low pressure pulls in more air from behind the machine (filling the gap) which is then in turn drawn into the air stream. That's called inducement.

The engineering challenge, however, is in keeping that stream of air flowing smoothly - balancing how fast the air is travelling (its "inertia") with how thick it is (its "viscosity"). Physicists have an equation which represents this balance, and it results in something called the Reynolds number.