[PDF] Class 9 notes science gravitation | extra questions class 9 science gravitation

Gravitation notes for class 9 and ncert Exemplar Class 9 Science extra questions

Hello guys, Do you know what is the most important material for a student? Let me tell you, The most important material for a student are notes.

So, in this article we will provide you class 9 notes of gravitation 2022 and the whole class 9 notes are handwritten and contain easy language. So that you can understand it carefully.

I guarantee you the  class 9 notes that I am providing you are better than study rankers, vedantu, byjus notes. 

Gravitation Class 9 Notes PDF Contain The Following Topics:

• Gravitational Force
• Newton's observations
• Universal law of gravitation
• Importance of universal law of gravitation
• What is Free Fall?
• Value of 'g' may vary at different parts of earth
• Calculation of g
• Difference between G and g 
• Equation of motion when an object is falling freely towards earth or thrown vertically upwards.
• Mass
• Weight
• Distinguish between Mass and Weight
• Weight of an object on moon 

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Class 9 notes gravitation pdf link and overview

• Gravitational force: all objects in this universe attract each other, this force of attraction is called Gravitational force.

• Newton's observations: 

▶Why does Apple fall on earth from a tree?

  Because earth attracts it towards itself 

▶Can apple also attract the Earth? Yes, it also attracts the earth as per Newton's third law [ every action has an equal and opposite reaction] But the mass of earth is much larger than apple therefore Earth never move towards it.

• Universal law of gravitation

Sir Isaac Newton in 1687 proposed a law about force of attraction between the two objects in the universe which is known as Newton's law of gravitation.

■ According to this law 

• Every object attracts each other object.
• This force is directly proportional to product of their mass.
• This force is inversely proportional to the square of distance between them 

Let m1 and m2 be the masses of two objects and distanced, then force of attraction between them

F∝ m1×m2

F∝ 1/d^2

From above equations, we can write as

F∝ 1/d^2

               

F= Gm1m2/d^2

Where G is the gravitational constant.

■ SI UNIT:    Nm^2 kg^-2

■ Value of G = 6.673×10^-11 Nm^2 kg^-2

■ Important of universal law of gravitation:

1. The force that binds us to the earth.
2. The motion of moon around the earth.
3. The motion of earth around the sun.
4. The tides due to moon in the sea.

■ What is Free Fall?

Whenever objects fall towards earth due to earth's gravity and no other force is acting upon it, the object is said to be in Free Fall.

During this free fall direction do not change but velocity continuosly changes which is called acceleration due to gravity.

• Denoted by 'g'
• SI unit = m/s^2 ( Same as acceleration )

■ Value of 'g' on the surface of earth:

We know that force acting on an Object 

1.  F = GMem/R^2

[ Me = mass of earth 

[ M = mass of object 

[ R = radius of object 

 

We also know from 2nd law of motion 

 2. F = mg        :{ F = ma, here a=g}

From equation (i) and (ii) we have

m×g = GMem/R^2

=> g = GMe/R^2

∴ When body is at distance 'r' from centre 

    then,

g = GM/r^2

■ Value of 'g' may vary at different parts of     earth 

• From equation = Gm/r^2, it is clear that value of g depends on r means distance of object from earth's centre.

• Because shape of earth is not a perfect sphere. It is flat at poles and bulged out at the equator 

• That's why, the value of 'g' is greater at the poles and lesser at the equator. But for convenience we take 'g' as constant.

■ Calculation of g:

g = Gm/R^2 

Mass of earth: 6×10^24 kg

Radius of earth: 6.4×10^6 m

= 6.673×10^-11×6.4×10^24 kg/( 6.4×10^6m)2

g = 9.8 ms^-2

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Extra questions class 9 science gravitation

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Previous year questions (PYQ) for class 9 gravitation pdf and overview

Also, Read

• Study time table for class 9 science
• Term 2 syllabus class 9
• Syllabus of class 9 CBSE 2021-2022
• Class 9 Science notes
• Class 9 sst notes
• Class 9 sample papers of science
• Class 9 social science syllabus
• Class 9 books review 

VERY SHORT ANSWER QUESTIONS

Question 1.

What do you mean by gravitation? (CBSE 2012)

Answer:

The force of attraction between any two particles in the universe is called gravitation.

Question 2.

State Universal law of gravitation. 

                           OR

How is the force of attraction dependent on the masses of objects and distance

between them ?

(CBSE 2014)

Answer:

Each object on the universe attracts other object with a’ force known as gravitational

force. The force of attraction between two objects is directly proportional to

1. the product of masses of the objects and

2. inversely proportional to the square of distance between them. That is, 

F = Gm1m2/r^2

Question 3.

The value of G = 6.673 x 10-11 Nm2 kg-2 on the surface of the earth. What is the value of G on the

surface of the moon ? (CBSE Sample Paper; CBSE 2011, 2013, 2014)

Answer:

The value of G on the surface of the moon

= value of G on the surface of the earth (i.e., 6.673 x 10-11 Nm2 kg-2).

Question 4.

Name the force which is responsible for the revolution of planets around the sun. (CBSE 2015)

Answer:

The gravitational force of attraction between the planet and the sun. This force provides the

necessary centripetal force to the planet to move in a circular orbit around the sun.

Question 5.

State two factors on which gravitational force between two objects depends.

Answer:

1. Mass of the objects,

2. distance between them.

Question 6.

The gravitational force between two objects is F. How will the force change when the

distance between them is reduced to 1/4 th ?

Answer:

F = Gm1m2/r^2 and F = Gm1m2/(r/4)^2 

= 16 Gm1m2/r^2 = 16F

Question 7.

Is the force of gravity stronger on a piece of iron than on a piece of wood if both have

the same mass ?

(CBSE 2015)

Answer:

No. Force of gravity on a piece of iron is equal to the force of gravity on a piece of wood

because F = mg.

Question 8.

When a stone is thrown vertically upwards, its velocity is continuously dedfeased. Why?

(CBSE 2015)

Answer:

When a stone is thrown vertically upwards, a force called gravitational force pulls the

stone continuously in the downward direction. Hence, velocity of the stone is decreased 

continuously.

Based on free fall and acceleration due to gravity.

Question 9.

The factor associated with the motion of an object are : Force, velocity, acceleration and

momentum. Out of these four factors which one remains constant for all bodies large or

small, undergoing a free fall.

(CBSE 2013, 2015)

Answer:

Acceleration of a freely falling object remains constant as it does not depend on the

mass of the object.

Question 10.

Is value of ‘g’ same at all ‘places on the earth ? Give reason for your answer. (CBSE

2011)

Answer:

No.

g = GM/R^2

Since polar radius (distance of pole from the centre of earth) is less than the equatorial

radius, therefore, the value of ‘g is more at poles than at equator.

I hope you like the class 9 extra questions science gravitation. Kindly practice them daily as much as you can. 

Now let's talk about ncert exemplar class 9 science.

Ncert Exemplar Solutions Class 9 gravitation Science

ncert exemplar solutions class 9 gravitation science, Exempler is the best book for class 9 term 2 science because the whole book is filled with important questions that really help you in your exams. 

Now let's get to the main topic without wasting time

Ncert exemplar solutions class 9 gravtation Science some important questions

ncert exemplar solutions class 9 gravitation science Multiple Choice Questions

1. Two objects of different masses falling freely near the surface of the moon would

(a) have same velocities at any instant

(b) have different accelerations

(c) experience forces of same magnitude

(d) undergo a change in their inertia

2. The value of acceleration due to gravity

(a) is same on equator and poles

(b) is least on poles

(c) is least on equator

(d) increases from pole to equator

3. The gravitational force between two objects is F. If masses of both objects

are halved without changing distance between them, then the gravitational

force would become

(a) F/4 (b) F/2 (c) F (d) 2 F

4. A boy is whirling a stone tied with a string in an horizontal circular path. If

the string breaks, the stone

(a) will continue to move in the circular path

(b) will move along a straight line towards the centre of the circular path

(c) will move along a straight line tangential to the circular path

(d) will move along a straight line perpendicular to the circular path away

from the boy

5. An object is put one by one in three liquids having different densities. The

object floats with

12 3 , and 9 11 7 parts of their volumes outside the liquid

surface in liquids of densities d1, d2 and d3 respectively. Which of the

following statement is correct?

(a) d1> d2> d3

(b) d1> d2< d3

(c) d1< d2> d3

(d) d1< d2< d3

6. In the relation F = G M m/d2, the quantity G

(a) depends on the value of g at the place of observation

(b) is used only when the earth is one of the two masses

(c) is greatest at the surface of the earth

(d) is universal constant of nature

7. Law of gravitation gives the gravitational force between

(a) the earth and a point mass only

(b) the earth and Sun only

(c) any two bodies having some mass

(d) two charged bodies only

8. The value of quantity G in the law of gravitation

(a) depends on mass of earth only

(b) depends on radius of earth only

(c) depends on both mass and radius of earth

(d) is independent of mass and radius of the earth

10. The atmosphere is held to the earth by

(a) gravity

(b) wind

(c) clouds

(d) earth’s magnetic field

11. The force of attraction between two unit point masses separated by a unit

distance is called

(a) gravitational potential

(b) acceleration due to gravity

(c) gravitational field

(d) universal gravitational constant

12. The weight of an object at the centre of the earth of radius R is

(a) zero

(b) infinite

(c) R times the weight at the surface of the earth

(d) 1/R2 times the weight at surface of the earth

 ncert exemplar solutions class 9 gravitation science Short Answer Questions

16. What is the source of centripetal force that a planet requires to revolve

around the Sun? On what factors does that force depend?

17. On the earth, a stone is thrown from a height in a direction parallel to the

earth’s surface while another stone is simultaneously dropped from the

same height. Which stone would reach the ground first and why?

18. Suppose gravity of earth suddenly becomes zero, then in which direction

will the moon begin to move if no other celestial body affects it?

19. Identical packets are dropped from two aeroplanes, one above the equator

and the other above the north pole, both at height h. Assuming all conditions

are identical, will those packets take same time to reach the surface of

earth. Justify your answer.

20. The weight of any person on the moon is about 1/6 times that on the

earth. He can lift a mass of 15 kg on the earth. What will be the maximum

mass, which can be lifted by the same force applied by the person on the

moon?

21. Calculate the average density of the earth in terms of g, G and R.

22. The earth is acted upon by gravitation of Sun, even though it does not fall

into the Sun. Why?

ncert exemplar solutions class 9 gravitation science Long Answer Questions

23. How does the weight of an object vary with respect to mass and radius of

the earth. In a hypothetical case, if the diameter of the earth becomes half

of its present value and its mass becomes four times of its present value,

then how would the weight of any object on the surface of the earth be

affected?

24. How does the force of attraction between the two bodies depend upon their

masses and distance between them? A student thought that two bricks

tied together would fall faster than a single one under the action of gravity.

Do you agree with his hypothesis or not? Comment.

25. Two objects of masses m1 and m2 having the same size are dropped

simultaneously from heights h1 and h2 respectively. Find out the ratio of

time they would take in reaching the ground. Will this ratio remain the

same if (i) one of the objects is hollow and the other one is solid and (ii) both

of them are hollow, size remaining the same in each case. Give reason.

26. (a) A cube of side 5 cm is immersed in water and then in saturated salt

solution. In which case will it experience a greater buoyant force. If

each side of the cube is reduced to 4 cm and then immersed in water,

what will be the effect on the buoyant force experienced by the cube as

compared to the first case for water. Give reason for each case.

(b) A ball weighing 4 kg of density 4000 kg m–3 is completely immersed in

water of density 103 kg m–3 Find the force of buoyancy on it. (Given g = 10 m s–2.)

I hope you like the ncert exemplar solutions class 9 science important questions for chapter gravitation.

FAQ TIME!

Question

What is gravitation Notes class 9?

Answer:

Universal law of gravitation: Sir Isaac Newton in 1687 proposed a law about force of attraction between the two objects in the universe which is known as Newton's law of gravitation.

Question

How many formulas are there in gravitation class 9?

Answer:

There are total of 8 Formulas in gravitation class 9.

F = G*M1 *m2 / r²

 g = G *M / R²

 v= u+GT.

 v² = u²+2gh.

 s= ut + 1/2 gt²

W= mg.

 pressure = thrust / area.

relative density = density of substance / density of water.

Question

What is gravitational force class 9 Ncert?

Answer:

Gravitational force: all objects in this universe attract each other, this force of attraction is called Gravitational force.

Question

How can I get class 9 notes?

Answer:

You can get best class 9 notes at Edugyane just search edugyane.in and click on the category of notes.

Question

How do you revise for class 9?

Answer:

You can revise and memorize your work last longer by doing practice of ncert exemplar and extra questions as much as you can.

Comment time

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You can answer these questions in the comment section.

Those who answer these questions within 3 days I will mention their any social media platform link and name on my next post and a free e-book also. So let's see who are the winners 

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Conclusion

I hope you understand the class 9 notes of gravitation, some important questions from ncert exemplar class 9 science, and thanks for reading the article till the end!