IntermediateTopic 47 of 105Thermodynamics & Fluids
Fluid statics
Pressure increases with depth as P=ρgh.
In depth
Pressure increases with depth: dP/dz=-ρg, so P=P₀+ρgh in a uniform fluid. Pascal's law: pressure applied to a confined fluid transmits equally. Basis of hydraulics, barometers and manometers.
Key points
- Pressure independent of container shape
- Absolute vs gauge
- Hydrostatic paradox
ExampleAt 10 m depth in water, gauge pressure is about 98 kPa.
Pressure in a static fluid increases with depth, which determines the forces on tanks, dams and divers and sets the design of containment.
What is Fluid statics?
Pressure increases with depth as P=ρgh.
Why is it important to understand fluid statics?
Pressure in a static fluid increases with depth, which determines the forces on tanks, dams and divers and sets the design of containment.
What is the pressure difference between two points in a static fluid?
It equals the density times gravity times the vertical height difference, so pressure grows linearly with depth.
Why does atmospheric pressure not appear in P equals rho g h?
It cancels in the difference between two points, unless you need absolute pressure at a point.
How is Fluid statics used in practice?
Typical applications include calculating the pressure at the bottom of a water tank, finding the pressure at a given depth of a dam wall and checking the pressure at a pipe outlet below a tank level.
What should I learn before Fluid statics?
Study "Viscosity" first (topic 46 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Fluid statics?
Pressure independent of container shape. Absolute vs gauge. Hydrostatic paradox.
Can you give an example of Fluid statics?
At 10 m depth in water, gauge pressure is about 98 kPa.
What comes after Fluid statics?
The next topic is "Manometers and pressure measurement", which builds directly on this one.
How difficult is Fluid statics?
It is classed as Intermediate in Thermodynamics & Fluids (topic 47 of 105). It is an intermediate topic. Work through the beginner topics in Thermodynamics & Fluids first.