Pascal's Law

  • Pascal’s law states that the pressure exerted anywhere in a confined incompressible liquid is transmitted equally in all directions irrespective of the area on which it acts and it always acts at right angles to the surface of containing vessel.
  • Applications of Pascal’s law are hydraulic machines such as
  1. Hydraulic press
  2. Hydraulic brakes
  3. Hydraulic jack (or lift)
  • Principle of hydraulic machine is that a small force applied on a smaller piston is transmitted to produce a large force on the bigger piston. Hydraulic machines act as a force multiplier.
  • A hydraulic press works on the principle that when force is applied on the piston, it exerts a pressure on the liquid contained in the cylinder.
  • According to Pascal’s law, this pressure is transmitted through liquid in tube to the piston of the other cylinder due to which the piston tends to move upwards.
  • As the area of cross section of cylinder is less than that of the cylinder, therefore to lift a large weight kept on other piston.
  • When no weight is placed on the piston, it rises up against a fixed roof with a force.
  • Hydraulic press is used mainly for
  1. Pressing cotton bales
  2. For extracting the juice from sugarcane
  3. For squeezing oil out of linseed and cotton
  4. For engraving monograms on goods.
  • Hydraulic jack (or lift) is used for lifting heavy vehicles such as cars, trucks etc., in service stations for their repairing. Hydraulic brakes used in cars also works on the principle of Pascal’s law.

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  • Q1

    The pressure in a liquid at

    Marks:1
    Answer:

    the same depth is the same in all directions

    Explanation:

    Pressure = hdg.

    Hence, for the same liquid and the same depth, pressure is the same and is independent of directions. Therefore, the pressure in a liquid at the same depth is the same in all directions.

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  • Q2

    Pascal’s law states that

    Marks:1
    Answer:

    the pressure applied to an enclosed liquid is transmitted equally to every part of the liquid

    Explanation:

    When a pressure is applied at a point in a confined fluid, it is transmitted equally in all directions. This is Pascal’s law.

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  • Q3

    What is a hydraulic press? How is it based on Pascal’s law? Also define mechanical advantage and obtain an expression for it.

    Marks:5
    Answer:

    Hydraulic press is based upon the principle of transmission of fluid pressure. In it, a small force can be used to balance a large force by making the area of the piston supporting the force larger than the area of the piston on which the effort is applied.


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  • Q4

    Write down any two uses of Hydraulic press.

    Marks:2
    Answer:

    Following are the two uses of hydraulic press:

    • It is used for servicing automobiles.
    • It is used for making holes in metals.


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  • Q5

    (a) State Pascal’s law of transmission of pressure in liquids.

    (b) Name two machines which are based on Pascal’s law.

    Marks:2
    Answer:

    (a) Pascal’s law states that ‘Pressure exerted anywhere in a confined, incompressible liquid is transmitted equally in all directions, irrespective of the area on which it acts.

    (b) Hydraulic press and hydraulic brakes are two machines that are based on Pascal’s law.

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