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Class 9 Gravitation NCERT Questions answer

Gravitational and buoyancy force class 9 physics (science Book)

  • Gravitation and the universal law of gravitation.
  • The motion of objects under the influence of gravitational force on the earth.
  • The weight of a body varies from place to place.
  • Conditions for objects to float in liquids.

1.When we move from the poles to the equator. Hence, the value of ‘ g ’ decreases. Why
Ans: The shape of earth is an ellipse so when we move from the poles to the equator the radius of the earth R increases. 
Hence, the value of ‘ g ’ decreases because value 'g' is inversely proportional to the radius of earth. g = GM/R^2

2. How does the force of gravitation between two objects change when the distance between them is reduced to half?
Answer: when the distance between the objects is reduced to half the gravitational force increases by four times the original force.

3.. The gravitational force acts on all objects in proportion to their masses. Why, then, a heavy object does not fall faster than a light object?
Answer: Acceleration due to gravity does not depend on mass of object. 

Hence, all bodies fall with the same acceleration provided there is no air or other resistance

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?
 
Answer: The earth attracts the moon with the same force with which the moon attracts the earth. 

This is because the gravitational force is a mutual force of attraction, and it obeys Newton's third law of motion, which states that "for every action, there is an equal and opposite reaction."

5. If the moon attracts the earth, why does the earth not move towards the moon?
 
Answer: Centripetal force due to circular motion in orbit and gravitatonal force  balance each other.
Therefore, the 🌎 and the 🌙 not moving towards each other ❣️

6. What is Gravitation?
 
Answer: Gravitation is the force of attraction between two objects in the universe and depends on masses of object and distance between objects. It only felt if objects are heavy

7. what is Centripetal force?
Answer: 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.

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