Bernoulli’s principle

Bernoulli’s principle is a law of physical science that explains the relationship between a fluid's pressure and velocity. The word fluid may refer to either a liquid or a gas. When the velocity of a fluid increases, its pressure decreases. Conversely, when the velocity of a fluid decreases, its pressure increases. Developed by Swiss scientist Daniel Bernoulli in the 1730s, this principle is readily observable in many real-world scenarios and has many practical applications. Most notably, the Bernoulli principle is an underlying concept in the science of flight. Moreover, the discovery of Bernoulli's principle was essential to the emergence of hydrodynamics, or the science of the motion of fluids, as a unique field of study.

Background

The Bernoulli principle was the work of Daniel Bernoulli, one of a family of Swiss scientists. Born in 1700, Bernoulli was the son of Johann Bernoulli, an accomplished mathematician. From an early stage, Bernoulli's relationship with his father was strained. The elder Bernoulli wanted his son to follow a profitable career path, but the younger was determined to pursue science. Eventually the younger Bernoulli got his way and quickly developed into an astute researcher.

In 1734, Bernoulli finished writing Hydrodynamica, his most famous work. Although it was not published until 1738, Hydrodynamica was a landmark accomplishment that led to the development of hydrodynamics, a new branch of physical science focused on the study of the motion of fluids. Unfortunately, the completion of Hydrodynamica also led to a further rift between Bernoulli and his father. Likely jealous of his son's success, the elder Bernoulli wrote a remarkably similar book called Hydraulica and allegedly predated it so that it appeared to have been written before Hydrodynamica. Regardless, Hydrodynamica eventually gained recognition as the leading early publication on hydrodynamics, most likely because the younger Bernoulli introduced a key principle within his historic work.

The Principle

In Hydrodynamica, Bernoulli provided a comprehensive study of the pressure, velocity, and equilibrium of fluids. Chief among the breakthroughs his work yielded was the discovery of the relationship between the pressure and velocity of a fluid. While observing what happened when various fluids flowed through a tube, Bernoulli noticed that the fluids always sped up when they flowed through narrower portions of the tube. Intrigued, Bernoulli investigated the occurrence more thoroughly and realized that the velocity of the fluid was related to its pressure. Specifically, he found that as the pressure of a fluid increases, its velocity decreases. This phenomenon, which came to be known as Bernoulli's principle, results when a fluid's energy shifts from potential energy to kinetic energy as the velocity of its flow increases.

Bernoulli's principle is observable in many situations, most notably as it applies to the concept of flight. Indeed, Bernoulli's principle is a key aspect of air travel. Airplane wings are shaped so that, when the airplane is in motion, air moves more quickly across the top of the wing, which decreases pressure above the wing. In contrast, air moves more slowly across the bottom of the wing, which causes pressure below the wing to increase. Because the pressure below the wings is greater than the pressure above the wings, the upward force on the plane is stronger. This force, known as lift, helps the airplane rise off the ground and remain aloft when moving at speed. While this is the most well-known example of Bernoulli's principle at work, it is far from the only one.

Bernoulli's principle is observable on a smaller scale in backyards everywhere. When using a garden hose, one can increase the velocity of the water flowing through the hose simply by closing off part of the flow cross section. Restricting the flow forces the water to travel through a smaller area in the same amount of time that it would have taken the water to pass through an unrestricted portion of the hose. Therefore, as a result of the increase in the water's velocity, the pressure at the edges of the flow decreases.

Another demonstration of Bernoulli's principle in the real world is the potentially dangerous situation that can result if two ships sail side by side. The gap between the ships narrows in the middle because of the unique shape of the ships' hulls. When water passes through the narrowest portion of the gap, its velocity naturally increases. In turn, the water pressure between the ships decreases while the water pressure on the outside of each ship remains strong. As a result of the difference in water pressure, the ships are pushed toward each other. If navigators fail to account for the pressure difference, a serious collision could result.

Impact

Bernoulli's work in the field of fluid dynamics and his discovery of the principle that bears his name have had an undeniably lasting influence. His efforts led to the creation of a whole new branch of science that has vastly improved understanding of the physical world. Moreover, application of the Bernoulli principle has led to technological advancements, including unlocking the secrets of flight.

Bibliography

"Bernoulli, Daniel (1700-1782)." Encyclopedia of Weather and Climate, Rev. ed. Ed. Michael Allaby. Vol. 1. New York: Facts on File, 2002, 66–68. Print.

"Bernoulli's Principle." Flight and Motion: The History and Science of Flying. Vol. 2. Armonk, NY: Sharpe Reference, 2009, 142–143. Print.

Pickover, Clifford. "Daniel Bernoulli." Archimedes to Hawking: Laws of Science and the Great Minds Behind Them. New York: Oxford University Press, 2008, 124–134. Print.

"Teaching from Space: The Bernoulli Principle." PBS LearningMedia. PBS & WGBH Educational Foundation. 2014. Web. 2 Dec. 2014. http://www.pbslearningmedia.org/resource/npe11.sci.phys.maf.bernoulli/teaching-from-space-the-bernoulli-principle/