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Gravitation

We all know the earth revolve around sun and it rotate on its own axis yet we don't feel the rotation and very surprising that we are on the crust yet we don't fall on space. This is all due to gravitation force, which holds every object on earth. Newton once saw apple falling down the tree, Question arises why this apple falls down not raised up word and small curiosity gives the concept of gravity.

Download pdf of NCERT Solutions for Class science Chapter 10 Gravitation

Download pdf of NCERT Examplar with Solutions for Class science Chapter 10 Gravitation

Exercise 1

Exercise 2

  • Q1

    What do you mean by free fall?

    Ans:

    A free fall motion means that the object is falling from a height under the influence of gravity only. It falls only due to its weight and not any other force. Provided these conditions the object experiences a free fall.

    It is observed that in a free fall; free - falling objects do not encounter air resistance.


    Q2

    What do you mean by acceleration due to gravity?

    Ans:

    When a body falls towards the earth from a height, then its velocity changes during the fall. This changing velocity produces acceleration in the body. This is called acceleration due to gravity. Its value is given by 9.8 m/s2.


Exercise 3

  • Q1

    What are the differences between the mass of an object and its weight?

    Ans:
    S. No. Mass Weight
    1 Mass is the property of matter. The mass of an object is the same everywhere. Weight depends on the effect of gravity. Weight increases or decreases with higher or lower gravity.
    2 Mass can never be zero. Weight can be zero if no gravity acts upon an object, as in space.
    3 Mass can never be zero. Weight is vector quantity. It is different at different places.
    4 It only has magnitude. It has magnitutde as well as direction.
    5 Its SI unit is kilogram (kg). Its SI unit is the same as the SI unit of force, i.e., Newton (N).

     


    Q2

    Why is the weight of an object on the moon 1/6th its weight on the earth?

    Ans:

    Our weight on the moon is less than it would be on Earth due to a difference of the strength of gravity on the moon. The moon’s gravitational force is determined by the mass and the size of the moon. Since the moon has significantly less mass than the Earth, it will not pull objects toward itself as the strength that Earth will. This means that if you went to the moon you would weigh less, even though your mass stays the same; 

    Let, ME = the mass of the Earth 

    m = an object on the surface of the Earth  

    RE = the radius of the Earth 

    WE = the object on the surface of the Earth


    Let, MM = mass of the moon 

     RM = radius of the moon

     WM = the object on the surface of the moon


    Where, ME = 5.98 x 1024 kg, MM = 7.36 x 1022 kg
    RE = 6.4 x 106 m, RM = 1.74 x 106 m
     

    Therefore, weight of an object on the moon is 1/6 of its weight on the Earth.

Exercise 4

  • Q1

    Why is it difficult to hold a school bag having a strap made of a thin and strong string?

    Ans:

    It is difficult to hold a school bag having a strap made of thin and strong string, because the thin string has very less contact area in case of a school bag having a strap made of thin and strong string which increases pressure which is uncomfortable to carry the school bag.


    Q2

    What do you mean by buoyancy?

    Ans:

    The upward force exerted by a liquid on an object that is partly or wholly immersed in it is known as buoyancy. Buoyancy is caused by the differences in pressure acting on opposite sides of an object immersed in a static fluid. It is also known as the buoyant force.


    Q3

    Why does an object float or sink when placed on the surface of water?

    Ans:

    An object sinks in water if its density is greater than that of water. This is because the buoyant force acting on the object is less than the force of gravity. On the other hand, an object floats in water if its density is less than that of water. This is because the buoyant force acting on the object is greater than the force of gravity.


Exercise 5

Exercise 6