Mechanical Properties of Fluids for JEE & NEET
Fluids, unlike solids, don’t have a fixed shape and can flow.
1. Pressure
- Definition: The force exerted per unit area by a fluid. P = F/A
- Units: Pascal (Pa) or N/m²
- Key characteristics:
- Pressure acts in all directions within a fluid.
- Pressure at a point in a fluid at rest is the same in all directions.
- Pressure increases with depth in a fluid due to the weight of the fluid above.
2. Pascal’s Law
- Statement: Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.
- Applications: Hydraulic lifts, hydraulic brakes.
3. Archimedes’ Principle
- Statement: When a body is immersed fully or partially in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced by the body.
- Buoyant force: The upward force exerted by a fluid on an immersed object.
- Applications: Ships floating, submarines, balloons.
4. Fluid Dynamics
- Study of fluids in motion: This includes understanding concepts like streamline flow, turbulent flow, viscosity, and surface tension.
- Equation of continuity: For an incompressible fluid flowing through a pipe of varying cross-section, the product of the area of cross-section and the speed of flow remains constant. A₁v₁ = A₂v₂
- Bernoulli’s principle: For an ideal fluid flowing in a streamline, the sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant along a streamline.
5. Viscosity
- Definition: A measure of a fluid’s resistance to flow. It arises due to internal friction between layers of the fluid.
- Coefficient of viscosity (η): A measure of the fluid’s viscosity.
- Newton’s law of viscosity: The shear stress between adjacent layers of a fluid is proportional to the velocity gradient.
- Effect of temperature: Viscosity of liquids generally decreases with increasing temperature, while the viscosity of gases generally increases with increasing temperature.
6. Surface Tension
- Definition: The property of the surface of a liquid that allows it to resist an external force due to the cohesive forces between molecules.
- Surface energy: The energy required to increase the surface area of a liquid by a unit amount.
- Applications: Formation of drops, capillary action, insects walking on water.
Mechanical Properties of Fluids for JEE & NEET