Page 122 - Understanding NCERT Science 09

• All objects experience a force of buoyancy when they are
immersed in a fluid.
• Objects having density less than that of the liquid in which
they are immersed, float on the surface of the liquid. If the
density of the object is more than the density of the liquid in
which it is immersed then it sinks in the liquid.

Exercises

1. How does the force of gravitation between two objects change
when the distance between them is reduced to half ?
2. Gravitational force acts on all objects in proportion to their
masses. Why then, a heavy object does not fall faster than
a light object?
3. What is the magnitude of the gravitational force between the
earth and a 1 kg object on its surface? (Mass of the earth is
6
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6 × 10 kg and radius of the earth is 6.4 × 10 m.)
4. The earth and the moon are attracted to each other by
gravitational force. Does the earth attract the moon with a
force that is greater or smaller or the same as the force
with which the moon attracts the earth? Why?
5. If the moon attracts the earth, why does the earth not move
towards the moon?
6. What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?
7. What is the importance of universal law of gravitation?
8. What is the acceleration of free fall?
9. What do we call the gravitational force between the earth and
an object?
10. Amit buys few grams of gold at the poles as per the instruction
of one of his friends. He hands over the same when he meets
him at the equator. Will the friend agree with the weight of gold
bought? If not, why? [Hint: The value of g is greater at the
poles than at the equator.]
11. Why will a sheet of paper fall slower than one that is crumpled
into a ball?

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12. Gravitational force on the surface of the moon is only as
6
strong as gravitational force on the earth. What is the weight
in newtons of a 10 kg object on the moon and on the earth?

GRAVITATION 111

Rationalised 2023-24