Gravitation Class 9 Notes Science - Chapter 10

Chapter: 10

What Are Gravitation ?

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    Gravitation

    Force between two objects or bodies which attract each other due to their masses

    Effects of Gravity

    Free fall

    • When an object falls down towards the earth under the gravitational force only.
    • Velocity of free falling body changes and is said to be acceleration due to gravity.
    • Acceleration due to gravity, ‘g’. Unit is m/s2. Value of g = 9.8 m/s2.
    Equation of Motion Acceleration due to gravity
    • v = u + gt
    • It is the gravitational attraction of earth
    • h = ut + gt2
    • g = 9.8 m/s2
    • v2 – u2 = 2gh
    • When a body is dropped freely from a height u = 0, g = 9.8 m/s2

    Universal Law of Gravitation

    • It states that every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance only.
    • F∝(Mm/d2)

    F =(GMm/d2) [ ∵ G = Universal gravitational constant]

    • SI unit of G = Nm2/Kg2
    • Value of G = 6.673 × 10–11 Nm2/Kg2

    Relation Between g And G

    • g =(GM/R2)

    (where G = gravitational constant, discovered by Cavendish

    M = Mass of the earth

    R = Radius of the earth)

    g =(6.7×10-11Nm2Kg–2 ×6 × 1024Kg/(6.4 × 10–6 m)2)

    • As the radium of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

    Mass And Weight

    Mass

    • Mass of an object is the measure of its inertia. (Scaler quantity)
    • It remains the same everywhere in the Universe.
    • SI Unit : Kg  

    Weight

    • Weight is the force of attraction of the earth on the object (vector quantity)
    • Weight of the body changes form place to place
    • W = mg
    • SI Unit: Newton (N)

    Thrust

    • Net force applied in a particular direction.
    • Depends on the area on which it acts.
    • SI Unit: Newton

    Archimedes’ Principle

    When a body is immersed fully or partially in a field, it experiences an upward force that is equal to the weight of the fluid displaced by it.

    Applications:

    • Used in designing ships and submarines
    • Used in lactomoters to find purity of milk.
    • Used in hydrometer to determine density of liquid.
    Upthrust Pressure
    • When an object is immersed in a fluid, they experience a buoyant force.
    • Force per unit area
    • Depends on the density of the fluid.
    • P =(F/A)
    • Upward force entered by liquid on a body.
    • Pressure =(Thrust/Area)
    • Density of object < density of liquid ⇒ object floats.
    • Density of object > density of liquid ⇒ object sinks.