Bernoulli’s principle formulated by Daniel Bernoulli states that as the speed of a moving fluid increases (liquid or gas), the pressure within the fluid decreases. Although Bernoulli deduced the law, it was Leonhard Euler who derived Bernoulli’s equation in its usual form in the year 1752.

Table of Contents: |

## What is Bernoulli’s Principle?

Bernoulli’s principle states that

The total mechanical energy of the moving fluid comprising the gravitational potential energy of elevation, the energy associated with the fluid pressure and the kinetic energy of the fluid motion, remains constant.

Bernoulli’s principle can be derived from the principle of conservation of energy.

## Bernoulli’s Principle Formula

Bernoulli’s equation formula is a relation between pressure, kinetic energy, and gravitational potential energy of a fluid in a container.

The formula for Bernoulli’s principle is given as follows:

Where p is the pressure exerted by the fluid, v is the velocity of the fluid, ρ is the density of the fluid and h is the height of the container.

Bernoulli’s equation gives great insight into the balance between pressure, velocity and elevation.

**Related Articles:**

## Bernoulli’s Equation Derivation

Consider a pipe with varying diameter and height through which an incompressible fluid is flowing. The relationship between the areas of cross-sections A, the flow speed v, height from the ground y, and pressure p at two different points 1 and 2 are given in the figure below.

**Assumptions:**

- The density of the incompressible fluid remains constant at both points.
- The energy of the fluid is conserved as there are no viscous forces in the fluid.

Therefore, the work done on the fluid is given as:

dW = F_{1}dx_{1} – F_{2}dx_{2}

dW = p_{1}A_{1}dx_{1} – p_{2}A_{2}dx_{2}

dW = p_{1}dv – p_{2}dv = (p_{1} – p_{2})dv

We know that the work done on the fluid was due to the conservation of change in gravitational potential energy and change in kinetic energy. The change in kinetic energy of the fluid is given as:

The change in potential energy is given as:

dU = m_{2}gy_{2} – m_{1}gy_{1} = ρdvg(y_{2} – y_{1})

Therefore, the energy equation is given as:

dW = dK + dU

Rearranging the above equation, we get

**This is Bernoulli’s equation.**

## Principle of Continuity

According to the principle of continuity

If the fluid is in streamline flow and is in-compressible then we can say that mass of fluid passing through different cross sections are equal.

From the above situation, we can say the mass of liquid inside the container remains the same.

The rate of mass entering = Rate of mass leaving

The rate of mass entering = ρA_{1}V_{1}Δt—– (1)

The rate of mass entering = ρA_{2}V_{2}Δt—– (2)

Using the above equations,

ρA_{1}V_{1}=ρA_{2}V_{2}

This equation is known as the Principle of Continuity.

Suppose we need to calculate the speed of efflux for the following setup.

Using Bernoulli’s equation at point 1 and point 2,

Generally, A

_{2}is much smaller than A

_{1}; in this case, v

_{1}

^{2}is very much smaller than v

_{2}

^{2}and can be neglected. We then find,

Assuming A_{2}<<A_{1},

We get, v_{2}=

Hence, the velocity of efflux is

## Bernoulli’s Principle Use

Bernoulli’s principle is used for studying the unsteady potential flow which is used in the theory of ocean surface waves and acoustics. It is also used for approximation of parameters like pressure and speed of the fluid.

The other applications of Bernoulli’s principle are:

**Venturi meter:**It is a device that is based on Bernoulli’s theorem and is used for measuring the rate of flow of liquid through the pipes. Using Bernoulli’s theorem, Venturi meter formula is given as:

\(\begin{array}{l}V=A_{1}A_{2}\sqrt{\frac{2hg}{A_{1}^{2}-A_{2}^{2}}}\end{array} \) |

**Working of an aeroplane:**The shape of the wings is such that the air passes at a higher speed over the upper surface than the lower surface. The difference in airspeed is calculated using Bernoulli’s principle to create a pressure difference.- When we are standing at a railway station and a train comes we tend to fall towards the train. This can be explained using Bernoulli’s principle as the train goes past, the velocity of air between the train and us increases. Hence, from the equation, we can say that the pressure decreases. So the pressure from behind pushes us towards the train. This is based on Bernoulli’s effect.

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

Conservation of energy is applied to the fluid flow to produce Bernoulli’s equation. The net work done results from a change in a fluid’s kinetic energy and gravitational potential energy. Bernoulli’s equation can be modified depending on the form of energy involved. Other forms of energy include the dissipation of thermal energy due to fluid viscosity.

### Bernoulli’s Equation at Constant Depth

When the fluid moves at a constant depth that is when h_{1} = h_{2}, then Bernoulli’s equation is given as:

\(\begin{array}{l}P_{1}+\frac{1}{2}\rho v_{1}^{2}=P_{2}+\frac{1}{2}\rho v_{2}^{2}\end{array} \)

### Bernoulli’s Equation for Static Fluids

When the fluid is static, then v_{1} = v_{2} = 0, then Bernoulli’s equation is given as:

When v_{1} = v_{2} = 0 |
P_{1} + ρgh_{1} = P_{2} + ρgh_{2} |

When h_{2} = 0 |
P_{2} = P_{1} + ρgh_{1} |

## Bernoulli’s Principle Example

**Q1. Calculate the pressure in the hose whose absolute pressure is 1.01 x 105 N.m-2 if the speed of the water in the hose increases from 1.96 m.s-1 to 25.5 m.s-1. Assume that the flow is frictionless and density 10^{3} kg.m^{-3}**

**Ans: **Given,

Pressure at point 2, p_{2} = 1.01 × 10^{5} N.m^{-2 }

Density of the fluid, ρ = 10^{3} kg.m^{-3}

Velocity of the fluid at point 1, v_{1} = 1.96 m.s^{-1}

Velocity of the fluid at point 2, v_{2} = 25.5 m.s^{-1}

**From Bernoulli’s principle** for p_{1},

Substituting the values in the above equation, we get

p_{1} = 4.24 × 10^{5} N.m^{-2}

## Frequently Asked Questions – FAQs

### What is Bernoulli famous for?

Daniel Bernoulli explained how the speed of fluid affects the pressure of the fluid, which is known as Bernoulli’s effect and explained the kinetic theory of gases. These two were his greatest contributions to Science, and the two concepts made him famous.

According to Bernoulli’s effect, he tried to explain that when a fluid flows through a region where the speed increases, the pressure will decrease. Bernoulli’s effects find many real-life applications, such as aeroplane wings are used for providing a lift to the plane.

### What does Bernoulli’s equation mean?

The Bernoulli equation is considered the statement of the energy conservation for the fluids that flow. This is considered to be the qualitative behaviour that lowers the pressure in the regions with high velocities. This is termed the Bernoulli effect.

### What is head loss in Bernoulli’s equation?

The head loss in Bernoulli’s equation represents the reduction in the total pressure, which is the sum of the velocity head, pressure head, and the elevation head of the fluid flowing through the hydraulic system.

### What is head loss equation?

The following equation is the mathematical representation of the head loss:

h_{L} = f L/D × v^{2}/2g

h_{L} = fLv_{2} / 2Dg

Where,

- h
_{L}is the head loss - f is the Darcy friction factor
- L is the pipe length
- D is inside pipe diameter
- v is the fluid velocity
- g is the gravitational constant

### What is the maximum suction head of a pump?

The maximum suction head of a pump is approximately 15 feet.

Hope you have understood the Bernoulli equation and its derivation and applications. To know more about various interesting science and maths topics, visit BYJU’S – The Learning App!.

good compilation

How to study bernoullis Theorem For A flow of incompressable non-vicous and a streamlined flow of fluid

This theorm is very good elaborated 😊😊

It seems to be a good explanation.

Nice

honestly speaking this is really helpful. I really appreciate the effort to illustrate it in the best way with the figures and all. and I guess putting a picture or a figure to describe how the plane works will be a great deal as Bernoulli is the main principle behind how a plane works