Archimedes Principle


 
 
Concept Explanation
 

Archimedes Principle

ARCHIMEDES PRINCIPLE:

Statement:  When an object is fully or partially immersed in a liquid, it experiences a buoyant force or upthrust which is equal to the weight of liquid displaced by the object, i.e. Buoyant force or upthrust acting on an object = Weight of liquid displaced by an object

Even gases like air, exert an upward force or buoyant force on the objects placed in them. It is buoyant force or upthrust due to displaced air which makes a balloon rise in air.

Applications of Archimedes Principle:

Archimedes principle is used in:

  • designing ships and submarines.
  • lactometer (a device used to determine the purity of milk).
  • hydrometer (a device used for determining the density of liquid).
  • determining the relative density of a substance.
  • Example: If an iron object is immersed in water, it displaces 8 kg of water. How much is the buoyant force acting on the iron object in newton? ( Given, g = 10 large ms^{-2})

    SOLUTION:  According to Archimedes principle, the buoyant force acting on this iron object will be equal to the weight of water displaced by this iron object.

    We know that, weight, w = m large times g

    Here, mass of water, m = 8 kg

    Acceleration due to gravity , large g=10;ms^{-2}

    On putting values, large w=8times10=80;N

    Since, the weight of water displaced by the iron object is 80 N, therefore the buoyant force acting on the iron object (due to water) will also be 80 N.

    How does a Boat Float in Water?

    A boat floats in water due to upward force called buoyant force (or upthrust) which is caused by the pressure of water pushing up the bottom of the boat. When boat is gradually lowered into water. It displaces more and more water. Hence, buoyant force on it also increases. When this buoyant force becomes just enough to support the weight of boat, the boat stops sinking down in water. Now,according to Archimedes principle, buoyant force is equal to the weight of liquid displaced by the boat. Hence, during the floating of the boat, the weight of water displaced by the submerged part of the boat is equal to the weight of the boat.

    Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    In which of the following Archimedes Principle is used ?

     

    Right Option : D
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    Explanation
    Question : 2

    Which o the following are correct :

    (a) When an object is fully or partially immersed in a liquid, it experiences a buoyant force or upthrust which is equal to the weight of liquid displaced by the object

    (b) Gases like air, exert an upward force or buoyant force on the objects placed in them. It is buoyant force or upthrust due to displaced air which makes a balloon rise in air.

    Right Option : C
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    Explanation
    Question : 3

    If an iron object is immersed in water, it displaces 10 kg of water. How much is the buoyant force acting on the iron object in newton? ( Given, g = 10 large ms^{-2})

    Right Option : B
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    Explanation
     
     


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