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Gravitation Class 9 PPT

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 Page 1


CHAPTER - 10
GRAVITATION
 
                              
                       
 
Page 2


CHAPTER - 10
GRAVITATION
 
                              
                       
 
1) Gravitation :-
   Gravitation is the force of attraction between two objects in the 
universe.
 i) Gravitation may be the attraction of objects by the earth.
    Eg :- If a body is dropped from a certain height, it falls downwards 
due to earth’s gravity.
            If a body is thrown upwards, it reaches a certain height and then 
falls downwards due to the earth’s gravity.
ii) Gravitation may be the attraction between objects in outer space.
   Eg :- Attraction between the earth and moon.
            Attraction between the sun and planets.
  Centripetal force :-
    When a body moves in a circular path, it changes its direction at 
every point. The force which keeps the body in the circular path acts 
towards the centre of the circle. This force is called centripetal force.
   If there is no centripetal force, the body will move in a straight line 
tangent to the circular path. 
Page 3


CHAPTER - 10
GRAVITATION
 
                              
                       
 
1) Gravitation :-
   Gravitation is the force of attraction between two objects in the 
universe.
 i) Gravitation may be the attraction of objects by the earth.
    Eg :- If a body is dropped from a certain height, it falls downwards 
due to earth’s gravity.
            If a body is thrown upwards, it reaches a certain height and then 
falls downwards due to the earth’s gravity.
ii) Gravitation may be the attraction between objects in outer space.
   Eg :- Attraction between the earth and moon.
            Attraction between the sun and planets.
  Centripetal force :-
    When a body moves in a circular path, it changes its direction at 
every point. The force which keeps the body in the circular path acts 
towards the centre of the circle. This force is called centripetal force.
   If there is no centripetal force, the body will move in a straight line 
tangent to the circular path. 
2) Universal law of gravitation :-
    The universal law of gravitation states that, ‘Every object in the universe 
attracts every other object with a force which is directly proportional to product 
of the masses and inversely proportional to the square of the distance between 
them.’
  Let two objects A and B of masses M and m lie at a distance d from each other. 
Let F be the force of attraction between them.
  According to the universal law of gravitation the force between the objects is 
directly proportional to the product of their masses and inversely proportional 
to the square of the distance between them.
                                          1                                                                 M x m
    F a M x m   and    F a  ---   Combining the two equations  F a  ----------
                                      d
2                                                                                                  
d
2
                                             
M x m
             Or  F = G  ---------    where G is a constant of proportionality called
                                  d
2            
universal gravitation constant   
                                                                                               F x d
2
   Cross multiplying we get  F x d
2  
= G M x m    or   G =  ---------
                                                                                               M x m
  The SI unit of G is N m
2
 kg 
-2
  and its value is  6.673 x 10
-11 
N m
2
 kg 
-2
 
M m
A
B
d
F
Page 4


CHAPTER - 10
GRAVITATION
 
                              
                       
 
1) Gravitation :-
   Gravitation is the force of attraction between two objects in the 
universe.
 i) Gravitation may be the attraction of objects by the earth.
    Eg :- If a body is dropped from a certain height, it falls downwards 
due to earth’s gravity.
            If a body is thrown upwards, it reaches a certain height and then 
falls downwards due to the earth’s gravity.
ii) Gravitation may be the attraction between objects in outer space.
   Eg :- Attraction between the earth and moon.
            Attraction between the sun and planets.
  Centripetal force :-
    When a body moves in a circular path, it changes its direction at 
every point. The force which keeps the body in the circular path acts 
towards the centre of the circle. This force is called centripetal force.
   If there is no centripetal force, the body will move in a straight line 
tangent to the circular path. 
2) Universal law of gravitation :-
    The universal law of gravitation states that, ‘Every object in the universe 
attracts every other object with a force which is directly proportional to product 
of the masses and inversely proportional to the square of the distance between 
them.’
  Let two objects A and B of masses M and m lie at a distance d from each other. 
Let F be the force of attraction between them.
  According to the universal law of gravitation the force between the objects is 
directly proportional to the product of their masses and inversely proportional 
to the square of the distance between them.
                                          1                                                                 M x m
    F a M x m   and    F a  ---   Combining the two equations  F a  ----------
                                      d
2                                                                                                  
d
2
                                             
M x m
             Or  F = G  ---------    where G is a constant of proportionality called
                                  d
2            
universal gravitation constant   
                                                                                               F x d
2
   Cross multiplying we get  F x d
2  
= G M x m    or   G =  ---------
                                                                                               M x m
  The SI unit of G is N m
2
 kg 
-2
  and its value is  6.673 x 10
-11 
N m
2
 kg 
-2
 
M m
A
B
d
F
3) Free fall :-
     The earth attracts objects towards it due to gravitational force. When an 
object falls towards the earth due to the earth’s gravitational force it is called 
free fall.
      When an object falls towards the earth there is a change in its acceleration 
due to the gravitational force of the earth. So this acceleration is called 
acceleration due to gravity.
     The acceleration due to gravity is denoted by g.
     The unit of g  is same as the unit of acceleration  ms 
-2
 From the second law of motion, force is the product of mass and acceleration.   
  
  F = ma 
 For free fall, force is the product of mass and acceleration due to gravity.            
            
                                    M x m                    M 
  F = mg   or  mg = G ---------   or  g = G ----  where M is the mass of the
                                       d
2                                    
d
2 
where M is the mass of the earth and d is the distance between the object and 
the earth.
  For objects near or on the surface of the earth d is equal to the radius of the 
earth R  
                                M x m                       M 
                 mg = G ----------     or  g =  G -----   The value of  g is  9.8 ms 
-2
                                  R
2                                    
R
2
Page 5


CHAPTER - 10
GRAVITATION
 
                              
                       
 
1) Gravitation :-
   Gravitation is the force of attraction between two objects in the 
universe.
 i) Gravitation may be the attraction of objects by the earth.
    Eg :- If a body is dropped from a certain height, it falls downwards 
due to earth’s gravity.
            If a body is thrown upwards, it reaches a certain height and then 
falls downwards due to the earth’s gravity.
ii) Gravitation may be the attraction between objects in outer space.
   Eg :- Attraction between the earth and moon.
            Attraction between the sun and planets.
  Centripetal force :-
    When a body moves in a circular path, it changes its direction at 
every point. The force which keeps the body in the circular path acts 
towards the centre of the circle. This force is called centripetal force.
   If there is no centripetal force, the body will move in a straight line 
tangent to the circular path. 
2) Universal law of gravitation :-
    The universal law of gravitation states that, ‘Every object in the universe 
attracts every other object with a force which is directly proportional to product 
of the masses and inversely proportional to the square of the distance between 
them.’
  Let two objects A and B of masses M and m lie at a distance d from each other. 
Let F be the force of attraction between them.
  According to the universal law of gravitation the force between the objects is 
directly proportional to the product of their masses and inversely proportional 
to the square of the distance between them.
                                          1                                                                 M x m
    F a M x m   and    F a  ---   Combining the two equations  F a  ----------
                                      d
2                                                                                                  
d
2
                                             
M x m
             Or  F = G  ---------    where G is a constant of proportionality called
                                  d
2            
universal gravitation constant   
                                                                                               F x d
2
   Cross multiplying we get  F x d
2  
= G M x m    or   G =  ---------
                                                                                               M x m
  The SI unit of G is N m
2
 kg 
-2
  and its value is  6.673 x 10
-11 
N m
2
 kg 
-2
 
M m
A
B
d
F
3) Free fall :-
     The earth attracts objects towards it due to gravitational force. When an 
object falls towards the earth due to the earth’s gravitational force it is called 
free fall.
      When an object falls towards the earth there is a change in its acceleration 
due to the gravitational force of the earth. So this acceleration is called 
acceleration due to gravity.
     The acceleration due to gravity is denoted by g.
     The unit of g  is same as the unit of acceleration  ms 
-2
 From the second law of motion, force is the product of mass and acceleration.   
  
  F = ma 
 For free fall, force is the product of mass and acceleration due to gravity.            
            
                                    M x m                    M 
  F = mg   or  mg = G ---------   or  g = G ----  where M is the mass of the
                                       d
2                                    
d
2 
where M is the mass of the earth and d is the distance between the object and 
the earth.
  For objects near or on the surface of the earth d is equal to the radius of the 
earth R  
                                M x m                       M 
                 mg = G ----------     or  g =  G -----   The value of  g is  9.8 ms 
-2
                                  R
2                                    
R
2
4a) Mass :-
    The mass of a body is the measure of its inertia. If the mass of a 
body is more its inertia is more.
    The mass of a body is constant and does not change from place to 
place.
    The SI unit of mass is kg.
b) Weight :-
    The weight of a body is the force with which the earth attracts the 
body.
    The force with which a body is attracted by the earth depends on its 
mass m and acceleration due to gravity g.
    F = m x g
    Since weight of a body is the force with which the earth attracts the 
body,  W = m x g
    Since g at a place is constant , W a  m
     The weight of a body changes from place to place.
    The SI unit of weight is the same as force – Newton (N). 
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FAQs on Gravitation Class 9 PPT

1. What is gravitation?
Ans. Gravitation is the natural phenomenon by which physical bodies attract with a force proportional to their mass. It is responsible for the attraction between objects on Earth, as well as the motion of planets, moons, stars, and galaxies.
2. Who discovered the concept of gravitation?
Ans. The concept of gravitation was discovered by Sir Isaac Newton, an English mathematician, physicist, and astronomer, in the late 17th century. His famous work "Principia Mathematica" explained the laws of gravitation and revolutionized our understanding of the universe.
3. How does gravitation affect the motion of objects?
Ans. Gravitation affects the motion of objects by exerting a force on them. This force, known as gravity, causes objects to fall toward the Earth's surface and influences the trajectory of celestial bodies. It is responsible for creating orbits and keeping planets and moons in their respective paths around the Sun.
4. What is the formula to calculate the force of gravitation between two objects?
Ans. The formula to calculate the force of gravitation between two objects is given by Newton's Law of Universal Gravitation: F = (G * m1 * m2) / r^2, where F is the force, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers of mass.
5. Can gravitation be felt on other planets or in space?
Ans. Yes, gravitation can be felt on other planets and in space. The force of gravity exists everywhere in the universe and affects all objects with mass. However, the strength of gravity may vary depending on the mass of the celestial body and the distance from its center. On other planets, the gravitational force may be stronger or weaker compared to Earth, leading to different experiences of weight and motion. In space, astronauts experience microgravity, where they feel weightless due to the absence of a strong gravitational force.
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