Pressure

Pressure

1. The force(thrust) acting normally on unit surface area

2. pressure = thrust/area

3. SI unit is pascal(Pa) or Nm^-3

4. Pressure in fluids

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   • Factors on which pressure at a point in a fluid depends
     • Pressure in a fluid is directly proportional to its height or depth
     • Pressure in a fluid is directly proportional to its density
     • Pressure in a fluid is directly proportional to the acceleration due to gravity
     • Pressure in a fluid is independent of the area of cross-section
   • LAWS OF LIQUID PRESSURE
     • Pressure at a point inside the liquid increases with the depth from the free surface of the liquid
     • Pressure at a point inside the liquid at a given depth increases with the increase in density of the liquid
     • Pressure is same in all directions, about a given point within the liquid
     • Pressure is same at all points in a horizontal plane at a given depth in a stationary object
     • A liquid seeks its own level
   • Pascal's law
     • states that whenever any pressure is applied to any part of the boundary of s confined fluid, it is transmitted equally in all directions irrespective of the area on which it acts , and always acts at right angles to the surface of containing vessel

5. is measured by Barometer

   • Mercury is used as a barometric liquid because
     • Vapour pressure of mercury is almost negligible and does not evaporate under vacuum conditions
     • Mercury is the densest liquid
     • Mercury is easily obtained in free state
     • Mercury is an opaque and shiny liquid . Thus can be easily seen in the glass tube
     • Mercury does not wet the sides of the glass tube which gibes the correct reading
   • Barometer was constructed by TORRICELLI
   • eg. Fortin's Barometer and Aneroid Barometer

6. Atmospheric Pressure

   • The force exerted by air on a unit surface are