Have you ever seen a human pyramid? Imagine the condition of the guy in the bottom-most row. He is obviously carrying a lot more load than the guy on the 1st row. The same is the case with fluid pressure in a column. In a fluid column, as the depth increases, the pressure increases as well. And why does this pressure increase? Because as you go deeper, fluid at a lower depth has to support fluid above it as well. Therefore to define it, we can say that
Fluid pressure is the pressure at a point within a fluid arising due to the weight of the fluid.
The pressure in fluids can be calculated using the following relation.
Pfluid = P + ρgh
P = Pressure at the reference point
Pfluid is the pressure at a point in a fluid
ρ is the density of the fluid
g is the acceleration due to gravity (considering earth g = 9.8 m/s)
h is the height from the reference point
The density of the fluid can be calculated by dividing the mass of the fluid in consideration with the volume of fluid taken.
ρ = m/v
m is the mass of the fluid
v is the volume of fluid considered
If the fluid is subject to atmospheric pressure than the total pressure on the system is given by
Pfluid = Po + ρgh
Po is the 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 considered in two conditions:
- In an open condition or open channel flow
- In a closed condition or closed conduit
The fluid pressure given above is the static fluid pressure or hydrostatic pressure. The pressure here is considered based only on the depth of fluid because the pressure produced due to fluid movement can be considered negligible. The static fluid pressure does not depend on the surface area, the shape of the fluid container or total volume and mass of the liquid.
Keep in mind that here, fluids refer to anything that has the ability to flow. Therefore, this refers to both liquids and gases.
- Calculate the pressure exerted on a scuba driver when she is 12 metres below the surface of the ocean. Assume the standard atmospheric condition.
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