Daniel Bernoulli (1700-1782) was a member of an important Dutch-Swiss family whose members were geniuses in mathematics and science. He discovered a principle of aviation which is known today asBernoulli’s Principle.
His principle states that the faster a fluid flows over a surface, or through a passage, the less pressure it exerts on its surrounding. This was Bernoulli’s great contribution to science.
Bernoulli’s family background
During the Reformation when Protestants were being persecuted in Belgium, Daniel Bernoulli’s great-great grandfather, Jacques Bernoulli, fled to Frankfurt, Germany. In 1622 his grandson went to Switzerland, and from that time the Bernoulli family brought fame to its adopted country. Nine members of the family were eminent in the fields of mathematics and science.
Four of these nine were honored by the Paris Academy of Sciences. The two greatest were the brothers Jacob and John, great-grandsons of Jacques Bernoulli, the one who fled to Belgium. Jacob was the fifth child in the family, and John, thirteen years younger, was the tenth child. John’s sons, Nicholas and Daniel, were able mathematicians under whose direction the great mathematician Leonhard Euler developed his mathematical genius.
In his work on hydrodynamics, Daniel Bernoulli laid the foundation of the kinetic, or moving, theory of gases. This, in turn, proved to be the basis of modern physical chemistry. The person who understands chemistry must understand the properties of gases. The understanding begins with the very simple truth that a gas is the simplest form of matter. In this state the molecules are most widely separated. Therefore, their action on one another is at a minimum.
This means that the number of causes which determine the properties of a gas must be fewer and less complex than those of a liquid or a solid. Boyle and Dalton discovered the laws which express the action of gases as a class when by themselves, but it was Bernoulli who first expressed in mathematical language the principles that govern the motion of molecules of matter in gases and liquids, and which produce such phenomena as osmosis, evaporation, energy conduction, and fluid pressure.
From Bernoulli’s work it has become possible to calculate the approximate number of molecules in any given volume at atmospheric pressure, their average distance apart, the average path of each, and the actual proportion of space—about 1/4000th part of the volume—occupied by them. From this the actual molecular volume itself could be easily calculated.
Very simply stated, Bernoulli’s Principle is: The faster a fluid flows over a surface, or through a passage, the less pressure it exerts on its surrounding. Air, then, is a fluid the pressure of which is lowered the faster it flows.
It is very interesting to note that collisions of ships have occurred because of this principle. If two ships are streaming side by side through still water, they are attracted toward one another.