Gravitation Class 9 Notes Science  Chapter 10
Chapter: 10
What Are Gravitation ?
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/s^{2}. Value of g = 9.8 m/s^{2}.
Equation of Motion  Acceleration due to gravity 







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/d^{2})
F =(GMm/d^{2}) [ ∵ G = Universal gravitational constant]
 SI unit of G = Nm^{2}/Kg^{2}
 Value of G = 6.673 × 10^{–11} Nm^{2}/Kg^{2}
Relation Between g And G
 g =(GM/R^{2})
(where G = gravitational constant, discovered by Cavendish
M = Mass of the earth
R = Radius of the earth)
g =(6.7×10^{11}Nm^{2}Kg^{–2} ×6 × 10^{24}Kg/(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 








