Buoyancy or Up thrust


 
 
Concept Explanation
 

Buoyancy or Up thrust

BUOYANCY OR UP THRUST:

The tendency of a liquid to exert an upward force on an object immersed in it is called buoyancy. Gases also exhibit this property of buoyancy.

Buoyant force is an upward force which acts on an object when it is immersed in a liquid. It is also called upthrust.

It is the buoyant force due to which heavy object seems to be lighter in water. As we lower the position of an object into a liquid, the greater upward pressure of liquid underneath it, provides an upward force.

e.g.  A piece of cork is held below the surface of water. When we apply a force by our thumb, the cork immediately rises to the surface. This is due to the fact that every liquid exerts an upward force on the objects immersed in it.

Note :

  • An object seems lighter when immersed in liquid. This reduced weight of an object in liquid is called apparent weight of an object.
  • The pressure exerted by a liquid increases with depth and acts in all directions (upwards also).
  • Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    Pressure at a certain depth in river water is P_1 and at the same depth in sea water is P_2. Then (density of sea water is greater than that of river water)

    Right Option : B
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    Explanation
    Question : 2

    A block of metal weighs 5N in air and 2N when immeresed in a liquid.The buoyant force is

    Right Option : A
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    Explanation
    Question : 3

    When a body is wholly or partially immersed in a liquid, it appears to lose weight. This loss of weight is equal to the weight of

    Right Option : B
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    Explanation
     
     


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