Air is a gas and water is a liquid, but scientist lump both into the category of fluids. A material is considered a fluid if the amount of force needed to change its shape is dependent on how quickly it changes. For a solid, the force needed to change its shape is dependent on how much it changes. For example, it takes the same amount of force to break a twig quickly as it does to break it slowly. But moving your hand through a body of water quickly will deform the liquid more than if you moved your hand through it slowly. The same phenomenon happens with air, as anyone who has ever stuck a hand out the window of a fast-moving car can attest.
Turbulence is what happens when the flow of air experiences a sudden change in wind speed or direction. This makes it bumpy instead of smooth. We can see turbulent flow in rivers and streams, or even when we stir cream into our morning cup of coffee. And most of us have experienced mild turbulence while flying in an airplane; the plane is flying through a "sea" of air, and sometimes the "waves" are choppy. Many things can cause turbulence: rising warm air, thunderstorms, even strong winds blowing over the tops of mountains, buildings and other objects in its way. Extreme turbulence is caused by severe thunderstorms, tornadoes, or hurricanes; airplanes usually divert their courses to avoid such areas.
Turbulence on flights can be annoying, but passengers are usually safe so long as they keep their seat belts fastened. The bumps and jolts don't really affect the aircraft or its flight path, unless the turbulence is quite severe. Severe turbulence can be avoided by flying around storm cells, or changing to a higher altitude.
What Are G Forces?
The physical sensations during turbulence are typical of roller coaster rides, thanks to "G" forces. The "G" stands for gravity, and a G force is a measure of acceleration. A coaster rider's inertia is separate from that of the car, so when the car speeds up, he feels pressed back against the seat because the plane is pushing him forward, accelerating his motion. When the plane slows down, the passenger's body tends to continue forward at the same speed in the same direction, but the restraining bar slows him down.
The American Meteorological Society contributed to the TV portion of this report.