# NCERT Class 9 Science Solutions: Chapter 10 – Gravitation Part 4

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Question 4:

Q. 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?

**Answer:**

According to the universal low of gravitation, two objects attract each other with equal force, but it opposite directions. The earth attracts the moon with an equal force with which the moon attracts the earth.

Question 5:

Q. If the moon attracts the earth, why does the earth not move toward the moon?

**Answer:**

The earth and the moon experience equal gravitational forces from each other. However, the mass of the earth is much larger than the mass of the moon. Hence, it accelerates at a rate lesser than the acceleration rate of the moon towards the Earth. For this reason, the Earth does not move towards the moon.

Question 6:

Q. What happens to the force between two objects, if

(i) The mass of one object is double?

**Answer:**

Double

According to the universal law of gravitation, the force of gravitation between two objects is given by:

is directly proportional to the masses of the objects. if the mass of one object is double, then the gravitational force will also get doubled.

(ii) The distance between the objects is double and triple?

**Answer:**

One-fourth and one-ninth

According to the universal law of gravitation, the force of gravitation between two objects is given by:

is inversely proportional to the square of the distance between the objects. If the distance is double, then the gravitational force becomes one-fourth of its original value.

Similarly, if the distance is tripled, then the gravitational force becomes one-ninth of its original value.

(iii) The masses of both objects are doubled?

Answer:

Four times

According to the universal law of gravitation, the force of gravitation between two objects is given by:

is directly proportional to the product of masses of the objects. if the masses of both the objects are double, then the gravitational force becomes four times the original value.

Question 7:

Q. What is the importance of universal law of gravitation?

Answer:

The universal law of gravitation proves that ever object in the universe attracts every other object.

The universal law of gravitation is important due to the following:

i) this law explains well the force that binds us to earth.

ii) this law describes the motion of planets around the sun.

iii) this law justifies the tide formation on earth due to moon and sun.

iv) this law gives reason for movement of moon around earth.