Pressure in Fluids

Pressure in Fluids

1. Thrust - Force acting normally on a surface

   • CGS - dynes
   • SI - Newtons

2. Lateral pressure acting on the walls of the container

3. Scalar quantity

4. Fluids exert pressure in all directions in the container

5. SI - newton per square metre(Pa)

6. Mathematical expression - h.p.g

   • h=height of the body
   • p=density of body
   • g=acceleration due to gravity

7. Transmission of Fluid pressure

   • Pascal's Law

8. How hydraulic brakes work

9. Hydraulic Press

10. Atmospheric Pressure

    • The atmosphere has various gases and hence exerts pressure on the surface of the Earth.
    • Force exerted by air on a unit surface area

11. Measurement of Atmospheric Pressure

    • A simple Barometer:
      • A glass tube with a narrow uniform bore of length 100cm
      • Closed at one end
      • Filled with perfectly pure and dry mercury
      • Thumb is placed on the open end an the tube is inverted in bowl containing mercury.
      • Empty space commonly formed on the tip of the tube called Torricellian vacuum

12. Factors affecting barometric pressure

    • Presence of moisture in mercury
    • Presence of dissolved metals in mercury
    • Vertical height fom sea level
    • Temperature of the atmosphere
      • Presence of moisture in air

13. Expressing atmospheric pressure in Pascal

    • 1.013 x 100000 Pa

14. Disadvantages of using water as a barometric liquid

    • Water barometer will support 10.34m of water at sea level .It is impractical to have such a a long tube
    • Water vaporises under vacuum conditions
    • Water sticks to the wall of glass tube and is transparent

15. Why is mercury used as a barometric liquid?

    • Vapour pressure of mercury is almost negligible at ordinary temperatures
    • Mercury is the densest liquid at ordinary temperatures
    • Mercury can be easily obtained in pure state.
    • Mercury is an opaque and shiny liquid
    • Mercury does not wet the sides of the glass tube

16. Fortin's Barometer

17. Effect of Atmospheric Pressure

    • The tremendous atmospheric pressure is not felt by humans as the blood pressure counterbalances it
    • the nose starts bleeding as the blood pressure is higher than the atmospheric pressure on higher altitude

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