Bernouilli, Daniel (1700-82)
Daniel Bernouilli was a member of a Swiss family that had more than its share of mathematicians and scientists. Daniel`s father, Jean Bernouilli (1667-1748), was a professor at Groningen (1695) and Basel (1705). Then there was Jean`s brother, Jacques Bernouilli (1654-1705), who, in 1698 published his work on differential calculus (he was the one who first used the term integral). Certain of Jean`s sons went on to teach at a number of universities located throughout Europe. The son we concern ourselves here with, is, Daniel Bernouilli. Daniel studied medicine and mathematics, but, eventually settled into teaching physics at Basel. He advanced our understanding of the physical world in a number of areas; but, it is in the kinetic theory of gases for which he is most remembered, particularly: the Bernouillis principle. It might be simply stated, as follows: "as the velocity of a fluid increases, its pressure decreases." Thus it was Daniel Bernouilli who showed that "the total energy in a steadily flowing fluid system is a constant along the flow path. Because the total energy is constant, an increase in the fluid`s speed must therefore be matched by a decrease in its pressure." The Bernouillis principle explains why a fixed wing airplane, once its moving in the air, and, because of the shape of the wing, will (usually) stay in the air. The Bernouillis principle might also be demonstrated by looking to a simple instrument to measure wind velocity. The instrument, in its simplest form, is a tube with a ball in it with the tube (the down side end) being closed and the other being open. When the wind blows over the top of the tube, a slight vacuum is created in the tube and the ball is sucked up. The stronger the wind, the greater the suction and the further up the tube the ball will travel.