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What is a Wake? You've probably heard some variation of the term "left in a wake," used to refer to someone or something which was sorely beaten in a race. However, a plane "left in a wake" is in a serious situation, which can be potentially dangerous to a small airplane. Vortices A vortex is a circulating cylinder of air; basically, a group of air spinning in a circle. Every wing attached to a plane which is flying produces vortices; it's impossible to have one without the other. Lift accompanies vortices, just as vortices accompany lift. A vortex is formed as air is pulled down over the wing of a plane. Since the wind is moving faster over the top of the wing, as it meets the air coming under the bottom of the wing, it spins into a vortex. 
As the vortices are formed coming off the wings, they form a wake vortex, which may extend for miles, of two long, horizontal cylinders of spinning air. Eventually, the two spinning vortices meet, and the vortex cancels itself out. Why is this a Problem? At first, it may appear that vortices are not a problem. They produce no effect on the plane which creates them, besides lift. What vortices can do is harm planes which enter their paths. A large, heavy plane creates a very strong vortex, one which potentially could flip a small plane 180°. The vortices create a spinning motion, one which can easily act on any object in its trail. Imagine feeling a 30 mph (48 km/hour) wind against your back. A wind of such magnitude, while it would likely not flip you over, would certainly push you around. The wake vortex off a very large plane can be many times as strong as this, and certainly strong enough to make a plane toss around. Whenever you feel a slight movement in the plane, or hear the pilot announce turbulence ahead, what he's really saying is that another plane has left a wake. In planes you fly in commercially, turbulence is hardly ever more than a slight annoyance, except in isolated incidents. However, for small planes, they are a potentially deadly phenomena which must be avoided. 
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