Hydrostatics Physics


Hydrostatics Physics

Archimede’s Principle Physics :

  • According to the principle when a body ( totally or partially ) immersed in a fluid, it appears to lose a part of its weight and the apparent loss of weight is equal to the weight of fluid displaced.
  • Apparent weight of body,

= Actual Weight of Body – Upthrust
= [mg – m / d x ρg]
= mg [1 – ρ / d]

  • where, d = density of body and ρ = density of fluid.
  • Buoyant force depends on the density of the fluid and not on the density of body acting on centre of gravity of fluid.

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Archimedes Law of Floatation :

  • When a body is immersed in a fluid then if :
    • The weight W of body is more than the up – thrust W’ ( W > W’ ), the body will sink.
    • The weight W of the body is equal to up – thrust W’ (W’ = W), the body floats with whole of its volume inside the liquid.
    • The weight ( W < W’ ), the body will float with some of its part outside the liquid.
  • When a block of ice floats in a liquid having density greater then that of water, the liquid level rises when all the ice melts into water.
  • When an ice block floats in a liquid of density less than that of water, the liquid level falls when all the ice melts into water.
  • When an ice block floats in water the water level will remain the same when all the ice melts into water.

Memorable Points :

  • Normal atmospheric pressure is equal to 76 cm of height of mercury in the Barometer.
  • If h is the barometric height for a liquid of density d, then,
hdg = 76 x 13.6 x g or h = 76 x 13.6 / d
  • Relative Density,
= Density of Body / Density of Water at 4°C
  • A pressure applied at any point of the fluid is equally transmitted in all the directions.
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