A fog machine is used to fill a drum made out of a bin. Hitting the drum forces air out of the hole, with the pressure differences within the air causing an air vortice.
The pressure differences are caused due to air slowing down as it rubs on the side of the hole. Areas of 'slow air' tend to move towards areas of 'fast air'... better put; high pressure moves to low presure. The mathematician
Bernoulli found that
moving air has less pressure than air that is still. There is a simple demonstration of this using a
funnel and a ping pong ball or you can try blowing
air between two balloons.
