The Bernoulli effect is a principle discovered by Daniel Bernoulli in 1738 that describes the relationship between flow velocity and pressure in fluid systems. As the velocity of horizontal flow through a fluid increases, the pressure decreases. This effect can be observed in both hydrodynamic and aerodynamic systems, and is used in real-world applications such as race cars, airplanes, carburetors, and sailing ships. The Bernoulli equation is a formal mathematical statement of the principle, and while there are different formulations, the effect is generally observable in every system.
The Bernoulli effect, or Bernoulli’s principle or Bernoulli’s law, is a statement of the relationship between flow velocity and pressure in a fluid system; in essence, as the velocity of horizontal flow through a fluid increases, the pressure decreases. This effect, and the principle that formally states it, was discovered by the famous mathematician Daniel Bernoulli, who first published his formulation in 1738. Since the word “fluid” in physics refers to the behavior of both liquids and gases, such as air, the Bernoulli effect can be observed both in hydrodynamic, or fluid, systems, and in aerodynamic, or gaseous systems.
A common example used to explain the Bernoulli effect is the flow of fluid through a pipe. If the fluid is moving uniformly through the pipe, the only forces acting on the fluid are its own weight and the fluid’s pressure. Now, if the pipe gets narrower, the fluid has to accelerate, because the same amount of fluid travels through a smaller space. However, if the fluid is moving uniformly and the weight hasn’t changed, the only way the fluid will move faster is if the pressure behind the fluid is greater than the pressure in front of it. Therefore, the pressure must decrease as the speed increases.
Since air can be considered a fluid (in physics, anything that flows is considered a fluid), the Bernoulli effect is frequently used in modeling aerodynamic systems. Race cars use the Bernoulli effect to keep them on the road at high speeds; by using a tail fin angled so that the air pressure above the fin is greater than below, the car is essentially held down by atmospheric pressure. This keeps the car on the road by negating drift and allows the driver greater control and confidence. Airplanes use the Bernoulli effect in the opposite way to help generate lift. Other common and real-world applications of the Bernoulli effect include carburetors, which apply the effect to draw in and mix air and fuel, and sailing ships, which can generate propulsive force from both wind and the pressure differential described by Bernoulli’s principle.
Although there are different formulations of the Bernoulli equation, which is a formal mathematical statement of the principle, the Bernoulli effect can be observed in any type of system described by the formulations. Each formulation describes a different set of fluid characteristics – incompressible flow, unstable potential flow, and so on – but the Bernoulli effect is generally observable in every system. However, there are some cases where the principle is invalid, and in those cases, the effect is as well.
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