Eddie Gilbertson age 16, of Lynn, Mass., for his question:

   CAN YOU EXPLAIN BERNOULLI'S PRINCIPLE?

   Bernoulli's principle in physics is the concept that as the speed of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases.

   The principle was originally formulated in 1738 by a Swiss physicist and mathematician named Daniel Bernoulli. He said that the total energy in a steadily flowing fluid system is a constant among the flow path. An increase in the fluids speed must therefore be matched by a decrease in its pressure.

The principle covers the flow over surfaces such as aircraft wings or ships' propellers. A wing is designed to permit air to flow more rapidly over its upper surface than over its lower surface, with a consequential reduced pressure on the top surface as compared to that on the bottom surface. The resulting pressure difference provides the lift that sustains the plane in flight.

On a rotating propeller, which is also shaped like an airfoil, the corresponding pressure difference provides the thrust that propels the vessel.