Fluid Statics
Pressure, Pascal's law, Archimedes' principle and buoyancy. (Physics › Properties of Bulk Matter, NEET UG syllabus.)
What is Fluid Statics?
The force applied perpendicular to the surface of an object per unit area over which that force is distributed.
Key formula / rule: Pressure
Key points
- Define pressure and understand its units.
- Explain how pressure varies with depth in a static fluid.
- State and apply Pascal's Law to hydraulic systems.
- State and apply Archimedes' Principle to determine buoyant force.
Common exam trap
Confusing absolute pressure with gauge pressure.
Definitions
- Term
Pressure
- Meaning
The force applied perpendicular to the surface of an object per unit area over which that force is distributed.
- Term
Absolute Pressure
- Meaning
The total pressure exerted on a system, including atmospheric pressure.
- Term
Gauge Pressure
- Meaning
The pressure relative to the ambient atmospheric pressure.
- Term
Pascal's Law
- Meaning
A principle stating that a pressure change at any point in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.
- Term
Archimedes' Principle
- Meaning
A principle stating that the buoyant force on a submerged or floating object is equal to the weight of the fluid that the object displaces.
- Term
Buoyancy
- Meaning
The upward force exerted by a fluid that opposes the weight of an immersed object.
- Term
Fluid
- Meaning
A substance that continually deforms (flows) under an applied shear stress, including liquids and gases.
Learning objectives
Define pressure and understand its units.
Explain how pressure varies with depth in a static fluid.
State and apply Pascal's Law to hydraulic systems.
State and apply Archimedes' Principle to determine buoyant force.
Analyze the conditions for an object to float, sink, or remain suspended.
Solve numerical problems involving pressure, buoyant force, and density.
Formulae
- Name
Pressure
- Note
Force (F) applied perpendicularly over area (A). Unit: Pascal (Pa) or N/m².
- Expression
P = F/A
- Name
Pressure variation with depth (Absolute Pressure)
- Note
P₀ is pressure at the surface, ρ is fluid density, g is acceleration due to gravity, h is depth.
- Expression
P = P₀ + ρgh
- Name
Gauge Pressure
- Note
Difference between absolute pressure and atmospheric pressure.
- Expression
Pgauge = Pabsolute - Patmospheric
- Name
Pascal's Law (Hydraulic Lift)
- Note
Pressure transmitted undiminished. F₁ is input force, A₁ is input area, F₂ is output force, A₂ is output area.
- Expression
F₁/A₁ = F₂/A₂
- Name
Buoyant Force (Archimedes' Principle)
- Note
ρfluid is density of the fluid, Vimmersed is volume of the object immersed in the fluid, g is acceleration due to gravity.
- Expression
FB = ρfluid × Vimmersed × g
- Name
Density
- Note
Mass (m) per unit volume (V). Unit: kg/m³.
- Expression
ρ = m/V
Prerequisites
Basic understanding of force, area, and density.
Knowledge of Newton's laws of motion.
Concept of weight and acceleration due to gravity.
Basic vector addition (for forces).
Common mistakes
Confusing absolute pressure with gauge pressure.
Incorrectly using the object's density instead of the fluid's density in Archimedes' principle.
Forgetting to convert units (e.g., cm to m, g to kg).
Assuming buoyant force acts only on fully submerged objects; it also applies to partially submerged ones.
Not considering atmospheric pressure when calculating absolute pressure at a depth.
Keywords
Pressure
Pascal's Law
Archimedes' Principle
Buoyancy
Fluid Statics
Density
Absolute Pressure
Gauge Pressure
Hydraulic Lift
Displaced Fluid
Practice preview
What is the SI unit of pressure?…
easy
A force of 100 N is applied uniformly over an area of 0.5 m^2. Calculate the pressure exerted.…
medium
Two points A and B are at the same horizontal level within a static fluid. Point A is in a wider section of the container, and point B is in a narrower section. Which statement about the pressure at A and B is correct?…
medium