Fluids at Rest- Pressure and Its Effects

Fluids at Rest- Pressure and Its Effects

1. Pascal's Law

   • Pressure at a point in a fluid at rest, or in motion, is independent of direction as long as there are no shearing stress.
   • Pressure at a point in a fluid at rest or in motion, is independent of direction as long as there are no shearing stress.

2. Basic Equation for Pressure Field

   • How does pressure in fluid vary from point to point (No shearing stresses) ?
     • Surface forces
     • Body force
     • General Equation of motion for a fluid (no shearing stresses)

3. Pressure Variation in a Fluid at Rest

   • fluid at rest, a=0
     • P depends only on z
   • Incompressible Fluid
     • Fluid with constant density
       • Pressure Difference
         • Pressure head
           • The height of a column of fluid of specific weight required to give a pressure difference.
   • Compressible Fluid
     • Density can change significantly with change in pressure and temperature.
     • Specific weights common gases are small.
     • Pressure gradient in vertical direction is small.

4. Measurement of Pressure

   • Concept of gage and absolute pressure
     • Gage pressure: measured relative to the local atmospheric pressure.
     • Absolute pressure: measured relative to a perfect vacuum.

5. Buoyant, Flotation and Stability.

   • Buoyang force: Resultant force acting on body, when a body completely submerged in a fluid or floating.
     • buoyant force equation:
   • Archimedes' Principle: buoyant force has a magnitude equal to the weight of the fluid displaced by the body and directed vertically upward.
   • Body position
     • Stable equilibrium: when displaced, it returns to its equilibrium position.
     • Unstable equilibrium: when displaced, it moves to a new equilibrium position.

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