Fluid Pressure - Hydrostatic Pressure

Human Pyramid

Have you ever seen a pyramid of people? Consider the person in the last row from the bottom. He is clearly carrying far more weight than the man in the front row. The fluid pressure in a column is the same way. The pressure in a fluid column rises in proportion to the depth. And why is there a rise in pressure? Because fluid at a lesser depth must also sustain fluid above it as you go deeper, In order to define it, we may thus state, “The pressure at a place within a fluid caused by the fluid’s weight is known as fluid pressure”.

Table of Contents

Calculation of fluid pressure

Fluid Pressure

  • Pfluid = P + ρgh
  • where,
    • P = Pressure at the reference point
    • Pfluid = Pressure at a point in a fluid
    • ρ = Density of the fluid
    • g = Acceleration due to gravity (considering earth g = 9.8 m/s)
    • h = Height from the reference point
  • The density of a fluid may be estimated by dividing its mass by the volume of fluid taken into account.
  • ρ = m/V
  • where,
    • m = Mass of the fluid
    • V = Volume of fluid considered
  • If the fluid is subject to atmospheric pressure, then the total pressure on the system is given by
  • Pfluid = Po + ρgh
  • where,
    • Po = Atmospheric pressure

If you prefer a video explanation of fluid pressure, then watch the video given below.

Conditions for the Consideration of Fluid Pressure:

Fluid pressure is examined in two situations:

  1. In an open condition or open channel flow
  2. In a closed condition or closed conduit

The fluid pressure listed above is hydrostatic pressure, often known as static fluid pressure. Because the pressure created by fluid movement may be regarded as minor, the pressure is simply taken into consideration here, depending on the depth of the fluid. The static fluid pressure is independent of the liquid’s volume, mass, total surface area, and container form.

Solved Example

  1. When a scuba diver is 12 metres below the ocean’s surface, determine the pressure that is placed on her. Pretend the atmospheric conditions are usual.

Factors that affect Fluid Pressure

Fluid pressure is influenced by two things. These two elements are the fluid’s depth and density.

  • The fluid’s depth: The pressure that the fluid exerts grows as the depth does as well.
  • The fluid’s density: In comparison to lighter fluids like air, denser fluids like water impose higher pressure.

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Frequently Asked Questions – FAQs


What does hydrostatic pressure mean in simple terms?

The pressure exerted by a fluid at equilibrium at any point due to the force of gravity.”
Because this is a definition-based question, there will be some ambiguity.

What causes fluids to exert pressure?

Fluid particles flow in all directions and provide pressure in all directions. Because of their mobility, these molecules are constantly colliding. As a result of the collision, pressure is applied in all directions.

What causes fluid to flow?

There are three factors that cause fluid to flow:
  1. Viscosity, density, and compressibility
  2. Speed of the flow
  3. Shape of the surface

What will increase gas pressure?

Temperature, pressure, number of molecules, and volume all affect gas pressure.
  1. When the number of molecules in the gas increases, there is an increase in gas pressure.
  2. When the volume decreases, the gas pressure increases.
  3. Temperature increases and the gas pressure increases.

How does gas pressure change with temperature?

We are aware that the average kinetic energy of the molecules in a gas directly relates to their temperature. The more molecules collide, the more pressure is generated in the gas as a result of the increase in kinetic energy.
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  1. I have a question
    How does acceleration due to gravity change pressure in fluids?

    • Hydrostatic pressure is the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to the depth measured from the surface because of the increasing weight of fluid exerting downward force from above.