Bernoulli’s, << buhr NOO leez, >> principle, also called Bernoulli’s law or Bernoulli’s theorem, states that energy is conserved in a moving fluid (liquid or gas). If the fluid is moving in a horizontal direction, the pressure decreases as the speed of the fluid increases. If the speed decreases, the pressure increases. For example, water moves faster through a narrow portion of a horizontal pipe than through a wider portion. Bernoulli’s principle predicts that the pressure will be lowest where the speed is greatest. Bernoulli’s principle was named for Daniel Bernoulli (1700-1782), a Swiss mathematician.
Bernoulli’s principle can explain how airplane wings create the upward force called lift and how a baseball pitcher can throw a curve ball. An airplane wing is shaped so the air speed above the wing is greater than the air speed below. This means the air pressure below the wing is greater than the pressure above, and the wing is pushed upward. In throwing a curve ball, a pitcher makes the ball spin fast. As a result, the air speed is greater on one side of the ball than on the other. The resulting difference in air pressure produces a net force toward the lower-pressure side and pushes the ball along a curved path.
