In the 1700's a Swiss scientist by the name of Daniel Bernoulli was studying the way fluids moved. His studies cultivated a single principle. The principle is that a fluid's energy equals the fluid's pressure times it's speed. (E=pv) This means that with more speed there is less pressure, and with less speed there is more pressure.
Bernoulli experimented with a device called a venturi tube. A
venturi tube is a tube with a fluid flowing through it that varies in
width. It looks something like Figure 1.
The tube demonstrates the principle because the particles have to
travel at a higher speed to pass through the smaller areas and
pressure is reduced.
Bernoulli's principle can be seen by taking a venturi tube and placing a small hole in the narrow part. The low pressure at this point will create an air flow inward as in Figure 2. This happens because the pressure outside the tube is less than inside at that point.
An example of Bernoulli's principle in the real world is a car passing by a truck. The wind rushing between the two vehicles acts like a venturi tube. Because the pressure is less between the two, the car is pushed toward the truck by air pressure on the other side of the car.
Another example of Bernoulli's principle is the airfoil. (Airfoils have many uses, but the most common is in the design of airplane wings.) The airfoil is similar to half of a venturi tube. The air above the wing acts like air inside the tube.The air below behaves like air outside the tube. When air goes around the airfoil, low air pressure results above the airfoil and normal air pressure is maintained below. This causes an upward force known as lift.
Back
to Aeronautics Lessons