## Bernoulli Principle – Class 11 | Chapter – 10 | Physics Short Notes Series PDF for NEET & JEE

Bernoulli Principle: Bernoulli principle is a fundamental concept in fluid dynamics, named after Swiss mathematician Daniel Bernoulli. It describes the relationship between the pressure and velocity of a fluid in motion. The principle states that as the speed of a fluid (such as air or water) increases, its pressure decreases. Conversely, as the speed of the fluid decreases, its pressure increases. This means that faster-moving fluids have lower pressure than slower-moving fluids.

This principle has many practical applications, such as in the design of airplane wings, where the curved shape of the wing causes air to move faster over the top of the wing than the bottom, resulting in lower pressure on the top of the wing and lift. It also explains how a vacuum cleaner works, where the air pressure inside the vacuum is lowered, causing higher pressure outside to push air and dust particles into the vacuum. Bernoulli principle is important in understanding how fluids move and how they interact with objects in their path.

## Formula of Bernoulli Principle

Bernoulli Principle describes the relationship between the velocity and pressure of a fluid. It states that as the velocity of a fluid increases, the pressure within the fluid decreases, and vice versa. The mathematical formula for Bernoulli Principle is:

P + 1/2 * rho * v^2 = constant

where:

• P is the static pressure of the fluid
• rho is the density of the fluid
• v is the velocity of the fluid.

The formula states that the sum of the static pressure and the dynamic pressure (which is proportional to the square of the fluid velocity) is constant at any given point in the fluid. This means that if the velocity of the fluid increases, the static pressure must decrease to maintain the constant sum.

Bernoulli Principle has many applications in physics and engineering, including in the design of aircraft wings, fluid dynamics, and the flow of fluids through pipes and channels.

## Limitations of Bernoulli Principle

While Bernoulli Principle is a powerful tool for understanding fluid flow and has many applications, there are some limitations to its use. Here are a few limitations:

• Incompressible fluids only: Bernoulli Principle is only applicable to incompressible fluids, which are fluids that do not change their density as they flow. In reality, many fluids, such as air, are compressible, which means their density can change with changes in pressure or temperature. Therefore, Bernoulli’s Principle is not as accurate when applied to compressible fluids.
• Steady-state flow only: Bernoulli Principle is valid only for steady-state flow, which means the fluid is flowing smoothly and without any turbulence. In reality, fluids can experience turbulence, which can lead to deviations from the predictions of Bernoulli Principle.
• Neglects frictional losses: Bernoulli Principle assumes that there are no energy losses due to friction between the fluid and the surface over which it flows. However, in reality, frictional losses are present, and these can cause deviations from the predictions of Bernoulli Principle.
• Neglects viscosity: Bernoulli Principle assumes that the fluid is inviscid, or has no internal friction. However, in reality, all fluids have some level of viscosity, which can affect fluid flow and lead to deviations from the predictions of Bernoulli Principle.

Despite these limitations, Bernoulli Principle remains a useful tool for understanding fluid flow and has many practical applications in engineering and physics. However, it is important to keep in mind its limitations and to use it appropriately for each specific situation.

## Principle of Continuity

The Principle of Continuity is a fundamental principle of fluid dynamics that states that mass must be conserved in a fluid as it flows through a pipe or channel. The principle is based on the fact that fluids are essentially incompressible, meaning that their density remains constant as they flow.

The principle can be stated mathematically as:

ρAV = ρAV

where:

• ρ₁ and ρ₂ are the densities of the fluid at two different points in the pipe or channel,
• A₁ and A₂ are the cross-sectional areas of the pipe or channel at the two points, and
• V₁ and V₂ are the velocities of the fluid at the two points.

The principle states that the mass of fluid flowing through any cross-section of the pipe or channel must be constant, regardless of changes in velocity or cross-sectional area. In other words, if the cross-sectional area of the pipe decreases, the velocity of the fluid must increase to maintain a constant mass flow rate.

The Principle of Continuity has many practical applications in engineering, including in the design of pipelines, channels, and hydraulic systems. It is essential for ensuring that fluids flow smoothly and efficiently through these systems, and for preventing problems such as blockages or pressure drops. The principle is also used in the design of aerodynamic systems, such as aircraft wings and wind turbines, where it helps to ensure that air flows smoothly over the surfaces of these structures.

## Relation Between Conservation of Energy and Bernoulli’s Equation

Conservation of energy and Bernoulli’s equation are closely related, as Bernoulli’s equation is a statement of the conservation of energy for a fluid in motion.

Bernoulli’s equation relates the pressure, velocity, and height of a fluid at any point along a streamline, and states that the total energy of the fluid remains constant along that streamline. Specifically, the equation states that the sum of the fluid’s kinetic energy, potential energy, and pressure energy is constant along the streamline.

Mathematically, Bernoulli’s equation can be written as:

P + 1/2 * rho * v2 + rho * g * h = constant

where:

• P is the fluid pressure,
• rho is the fluid density,
• v is the fluid velocity,
• g is the acceleration due to gravity, and
• h is the height above a reference point.

This equation expresses the conservation of energy for a fluid flowing along a streamline. As the fluid moves through a pipe or channel, for example, the total energy of the fluid remains constant along that streamline, and energy can be converted between the different forms of energy (kinetic, potential, and pressure) as the fluid flows.

Therefore, Bernoulli’s equation is a powerful tool for understanding fluid flow and the conversion of energy within fluids. It has many practical applications in engineering, including in the design of pipelines, channels, and hydraulic systems, where it is used to optimize fluid flow and energy efficiency.

## Bernoulli’s Equation at Constant Depth

When a fluid flows in a horizontal pipe or channel, its depth is constant, which means that the potential energy term in Bernoulli’s equation can be simplified. In this case, the Bernoulli’s equation becomes:

P₁ + 1/2 * ρ * v₁² = P₂ + 1/2 * ρ * v₂²

where:

• P₁ and P₂ are the pressures at two different points along the pipe or channel,
• ρ is the density of the fluid, and
• v₁ and v₂ are the velocities of the fluid at the two points.

This equation states that the sum of the pressure and kinetic energy of the fluid remains constant along a streamline when the depth is constant. It also implies that as the fluid velocity increases, the pressure decreases, and vice versa.

This equation has many practical applications in fluid dynamics, such as in the design of pipelines, channels, and hydraulic systems, where it is used to calculate the pressure and velocity of fluids at different points in the system. It is also used in aerodynamics, such as in the design of aircraft wings, to understand the relationship between air speed and pressure.

However, it is important to note that this equation assumes that the fluid is incompressible and that there are no energy losses due to friction or other factors. In reality, fluids may not be completely incompressible, and energy losses due to friction can occur. Therefore, the equation should be used with caution and with an understanding of its limitations.

## Bernoulli’s Equation for Static Fluids

Bernoulli’s equation applies to fluids in motion, so it cannot be used to describe the behavior of static fluids. However, the hydrostatic equation can be used to describe the behavior of fluids at rest.

The hydrostatic equation relates the pressure of a fluid to the depth of the fluid and the density of the fluid. It can be written as:

P = ρgh

where:

• P is the pressure of the fluid,
• ρ is the density of the fluid,
• g is the acceleration due to gravity, and
• h is the depth of the fluid.

This equation states that the pressure of a fluid increases with depth, due to the weight of the fluid above it. It also implies that the pressure at any point in a static fluid is the same in all directions.

The hydrostatic equation has many practical applications in engineering and science, such as in the design of hydraulic systems, the study of atmospheric pressure, and the measurement of fluid density. It is an important tool for understanding the behavior of fluids at rest, and it can be used in combination with Bernoulli’s equation to analyze the behavior of fluids in motion.

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