NCERT Solutions for Class 9 Science Chapter 9 – Gravitation

Gravitation is a fundamental force of nature that attracts every object towards every other object in the universe. It is responsible for keeping planets in their orbits, objects on the Earth’s surface, and governing the motion of celestial bodies.

This chapter explains the universal law of gravitation, acceleration due to gravity, mass and weight, and concepts like buoyancy and thrust. Understanding gravitation helps students connect physical laws with real-life phenomena such as falling objects, tides, and floating bodies.

NCERT Solutions for Class 9 Science Chapter 9 – Gravitation

Gravitation
Medium
Q.
How does the force of gravitation between two objects change when the distance between them is reduced to half?
Gravitation
Difficult
Q.
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.
Gravitation
Medium
Q.
The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm−3, will the substance float or sink?
Gravitation
Medium
Q.
Why does a block of plastic released under water come up to the surface of water?
Gravitation
Easy
Q.
In what direction does the buoyant force on an object immersed in a liquid act?
Gravitation
Medium
Q.
A ball thrown up vertically returns to the thrower after 6 s. Find
(a) the velocity with which it was thrown up,
(b) the maximum height it reaches, and
(c) its position after 4 s
Gravitation
Difficult
Q.
A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.
Gravitation
Difficult
Q.
Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 1024 kg and of the Sun = 2 × 1030 kg. The average distance between the two is 1.5 × 1011 m.
Gravitation
Medium
Q.
A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
Gravitation
Difficult
Q.
A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate
(i) the maximum height to which it rises.
(ii) the total time it takes to return to the surface of the earth.
Gravitation
Medium
Q.
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 × 1024 kg and radius of the earth is 6.4 × 106 m.)
Gravitation
Difficult
Q.
Gravitational force on the surface of the moon is only  1 6 MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0le9yqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeaacaGaaiaabeqaamaabaabaaGcbaWaaSaaaeaacaqGXaaabaGaaeOnaaaaaaa@376B@ as 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
Easy
Q.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Gravitation
Easy
Q.
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.]
Gravitation
Easy
Q.
What do we call the gravitational force between the Earth and an object?
Gravitation
Easy
Q.
What is the acceleration of free fall?
Gravitation
Medium
Q.
What is the importance of universal law of gravitation?
Gravitation
Medium
Q.
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?
Gravitation
Medium
Q.
If the moon attracts the earth, why does the earth not move towards the moon?
Gravitation
Medium
Q.
The volume of a 50 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1 g cm−3? What will be the mass of the water displaced by this packet?

NCERT Solutions for Class 9 Science Chapter 9 – Gravitation

NCERT Solutions for Class 9 Science Chapter 9 – Gravitation (Q&A)

Q1. Why does a heavy object not fall faster than a light object?

Ans: All objects fall with the same acceleration due to gravity, which is constant and independent of mass. Therefore, heavy and light objects fall at the same rate.

Q2. Does the Earth attract the Moon with greater, smaller, or equal force compared to the Moon attracting the Earth?

Ans: The Earth and the Moon attract each other with equal gravitational force but in opposite directions, as per the universal law of gravitation.

Q3. Why does the Earth not move towards the Moon?

Ans: Although both exert equal forces, the Earth has a much larger mass, so its acceleration is very small. Hence, the Earth does not move noticeably towards the Moon.

Q4. What happens to the gravitational force if:

(i) Mass of one object is doubled?

Ans: The force becomes double.

(ii) Distance between objects is doubled or tripled?

Ans:

  • If doubled → Force becomes one-fourth
  • If tripled → Force becomes one-ninth

(iii) Masses of both objects are doubled?

Ans: The force becomes four times.

Q5. What is the importance of the universal law of gravitation?

Ans:

  • It binds us to the Earth
  • Explains motion of Moon around Earth
  • Explains motion of planets around the Sun

Q6. What is acceleration of free fall?

Ans: It is the acceleration of an object falling under gravity. Its value near Earth’s surface is 9.8 m/s², and it is constant for all objects.

Q7. What is the gravitational force between Earth and an object called?

Ans: It is called the weight of the object.

Q8. Will the weight of gold change from poles to equator?

Ans: Yes. Weight is slightly less at the equator because the value of acceleration due to gravity (g) is lower compared to the poles.

Q9. Why does a sheet of paper fall slower than a crumpled ball?

Ans: A sheet of paper experiences more air resistance due to its larger surface area, causing it to fall slower than a crumpled ball.

Q10. In which direction does buoyant force act?

Ans: Buoyant force acts in the upward direction on an object immersed in a liquid.

Q11. Why does a plastic block rise to the surface in water?

Ans: The upward buoyant force acting on the block is greater than the downward gravitational force, causing it to float.

FAQs

Q1. What is gravitation?

Gravitation is the force of attraction between any two objects in the universe.

Q2. What is the universal law of gravitation?

It states that every object attracts every other object with a force proportional to their masses and inversely proportional to the square of the distance between them.

Q3. What is acceleration due to gravity (g)?

It is the acceleration of an object falling freely under gravity, approximately 9.8 m/s² near Earth’s surface.

Q4. What is weight?

Weight is the force exerted by gravity on an object.

Q5. What is buoyancy?

Buoyancy is the upward force exerted by a fluid on an object immersed in it.

Q6. Why do objects float in water?

Objects float when the buoyant force acting on them is greater than or equal to their weight.

Q7. Why does weight vary from place to place?

Weight depends on the value of gravity (g), which varies slightly with location (e.g., poles vs equator).