NCERT 9th class solution :Concept of Gravitational force

Updated Tue, 20 Jun 2023 04:44 PM IST

Highlights

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 Gravitational force: Introduction

 
It is said that when Newtonn was sitting under a tree ,an apple fell over his head .he thought that if the earth can attract an apple, can it not attract the moon? Is the force the same in both cases? To prove this fact he analyses many data about the motion of the moon around Earth. The earth attracts everything towards itself. This happens due to the rotational force exerted by Earth whenever objects fall towards the earth under the earth’s gravitational force alone are called freely falling bodies and such a fall is called free fall.
 
The force of which we are constantly aware in our daily life is that which pulls us up towards earth it is defined as the non-contract force of attraction between any two bodies in the universe no matter how far are the bodies.

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The universal law of gravitation

 
Based on his findings Newton give a new known as Newton’s law of gravitational or universal law of gravitation. This law state that every particle of matter in the universe attracts every other particle with a force which is directly proportional to the products of their masses and inversely proportional to the square of the distance between them.
Demonstration of gravitational between two objects of different masses.
 
If two object A and B with masses M1 and M2 and respectively with their Centre separated by d and F the gravitational force of attraction between them.
 
Then F o< M1×M2÷1
& F o< 1÷ d²
Or F = G M1M2÷ d²
 
Where G is the constant of proportionally and is called the universal. gravitational constant the value of g is constant everywhere and hance it is called universal constant of gravitation.
 

Importance of the universal law of gravitation

 
The gravitational force is responsible for
1.

Source: Amar ujala

Winding all terrestrial object on earth
2. The motion of moon around Earth
3. The existence of the solar system
4. The formation of tides
5. The flow of water in river
6. The rainfall and the snowfall on earth
7. Holding the atmosphere near the earth surface.
 

Gravitational force: definition

 
The force of attraction that move the body towards the centre of earth is called gravity or gravitational force.
 

Centre of gravity

 
Any particle body for example stone may be regarded as being made up of a very large number of tiny equal particles of mass. Each one of pulled by the earth with the force .On this side the gravitational force acting on all the particles of the stone will be equal.
 
We know F= ma
Then mg+ mg+ mg + mg………..= mg= W( resultant force)
 
 The force acting at the center in the center of the stone is called the Center of Gravity. And it’s denoted by G.
 
The point of application of the resultant force on a body due to Earth’s attraction on it is called the centre of gravity of that body. The resultant force is called the weight of the body.
 

Relation between G and g

 
Buy Newton's law of gravitational
F= G M× m÷ d²…….a
 
And according to the Newton’s second law of motion
F= ma
 
From equation a& bg= GM÷ d² if the body is near on the surface of Earth then the distance will be equal to the radius of Earth,so
G = GM.÷ R²
 

Important fact about the gravitational force

 
• The direction of G is along the line joining the body and the centre of earth.
• The value of g at the poles is greater than equator because the radius of earth at pole is less than that at equator.
• The value of g decrease with increase in altitude above the surface of Earth.
• At the centre of earth the value of g is zero.
• The value of g varies from place to place on the surface of earth because Earth is not a perfect sphere.
• If body falls from rest freely under gravity the initial velocity u is considered as zero.
• That time taken by a body to rise to the highest point is equal to the time taken by the body to the come back to its initial point after reaching the highest point.
Time of rise= time of fall.

Stability

 
The stability of a body depends on the following
• Position of the centre of
• Area of its base
1. For stable body the centre of gravity should be as low as hence to increase the stability the lower part of the body should be made heavy.
2. The base area of the body should be large so the vertical line through the centre of the gravity of the body passes through its base. If a body is slightly tilted it centre of gravity rises higher and it has a tendency to regain its original position to lower the centre of gravity.

Q1- what is gravitational force?

Answer -Definitions of gravitational force. (physics) the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near its surface. synonyms: gravitation, gravitational attraction, gravity. types: solar gravity. the gravity of the sun.

Q2- what are the three example of gravitational force?

Answer- Some examples of the force of gravity include:
The force that holds the gases in the sun.
The force that causes a ball you throw in the air to come down again.
The force that causes a car to coast downhill even when you aren't stepping on the gas.
The force that causes a glass you drop to fall to the floor.

Q-3 what is called gravitational?

Answer- gravity, also called gravitation, in mechanics, the universal force of attraction acting between all matter. It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter.

Q-3 how gravity is formed?

Answer- Einstein suggested that the shape of spacetime is what gives rise to the force we experience as gravity. A concentration of mass (or energy), such as the Earth or sun, bends space around it like a rock bends the flow of a river.

Q4-is gravity force or energy?

 Answer -Forces are the way that energy is transferred from one object to another when they interact, but forces are not the energy itself. Gravity is a force, so it just provides one way for objects to exchange and transform energy to different states.

Q5-why is gravity so important?

Answer-Gravity is a very important force. Every object in space exerts a gravitational pull on every other, and so gravity influences the paths taken by everything traveling through space. It is the glue that holds together entire galaxies. It keeps planets in orbit.

Q6-why does mass create gravity?

Answer-According to theory, the reason mass is proportional to gravity is because everything with mass emits tiny particles called gravitons. These gravitons are responsible for gravitational attraction. The more mass, the more gravitons.

Q7- what will happen without gravity?

Answer-Humans and other objects will become weightless without gravity. If we have no gravity force, the atmosphere would disappear into space, the moon would collide with the earth, the earth would stop rotating, we would all feel weightless, the earth would collide with the sun, and as a consequence. We would all perish.

Q8-can we live without gravity?

Answer- It might seem like a fantasy to float weightlessly through the air but practically, the human body would go through negative change, such as muscle and bone atrophy while living in zero gravity. Even the rivers, lakes and oceans on Earth wouldn't stand in zero gravity, without which humans cannot survive.

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