# Gravitation Class 11th Notes - Free NCERT Class 11 Physics Chapter 8 notes - Download PDF

Three units, Unit - IV Work, Energy, and Power, Unit - V Motion of System of Particles, and Unit - VI Gravitation, will be combined for a total of 17 points, according to the latest CBSE Syllabus. Class 11 Physics chapter 8 notes gravitation is one of the most essential chapters in the syllabus of competitive exams such as NEET and JEE.

This NCERT Class 11 Physics chapter 8 has a 2% weighting in NEET, and you can expect one question from it in the JEE Main test. You've come to the right site if you're seeking for dependable, easy-to-understand Gravitation Class 11 notes pdf download. Galaxies, stars, planets, comets, asteroids, and meteoroids are all components of the cosmos. In NCERT notes for Class 11 Physics chapter 8, the gravitational force is discussed, the force that binds things together. Material objects are attracted to one another by gravity, which is a natural phenomenon.

Sir Isaac Newton, an English physicist, released Principia Mathematica in 1687 A.D., which describes the inverse-square law of gravitation. Class 11 Physics chapter 8 notes also cover the basic equations in the chapter. The necessary derivations are not covered in the CBSE Class 11 Physics chapter 8 notes.

**Also, students can refer,**

- NCERT Solutions for Class 12 Physics Chapter 8: Gravitation
- NCERT Exemplar Solution Class 12 Physics Chapter 8: Gravitation

**Newtons Law of Gravitation**

Definition

Every particle of matter attracts each other with a force proportional to its masses multiplied by the square of its distance.

Mathematical Form

If m_{1} and m_{2} are the particle’s masses and the distance between them is r, the force of attraction Famong the particles is given by

(G is the universal constant of gravitation.)

Vector Form

The force F_{21} exerted on the particle m_{2} by the particle m_{1} is given by:

Where r_{12} cap is a unit vector drawn from particle m_{1} to particle m_{2}

Similarly,

**Universal Constant for Gravitation**

Universal gravitation constant is given as

**S.I. unit**

**C.G.S. unit **

**Value of G**

**Dimensions of G**

**Variation in ‘g’**

Condition: Gravitational Acceleration Above the Earth's Surface

Let M and R be the mass and radius of the earth, respectively, and g signify the gravity-induced acceleration at the surface. Assume a mass of m is placed on the surface of the earth.

The body's mass,' mg,' is the same as the gravitational force acting on it.

Assume the body is now raised to a height h above the earth's surface, its weight is now mg, and the gravitational force acting on it is:

Dividing,

Gravitational acceleration at a Very Small Height

If h << R, then neglecting high powers of ‘h’ we get

**Satellite**

A satellite is a smaller body that spins around a larger body under the influence of its gravitation. It could be natural or man-made.

1. Because the moon revolves around the earth, it is considered a satellite. Jupiter has a total of sixteen satellites orbiting it. These satellites are referred to as natural satellites.

2. A human-built artificial satellite is one that has been sent into a circular orbit. The first satellite, SPUTNIK–I, was launched by the Soviet Union, whereas the first satellite, ARYABHATTA, was launched by India.

Minimum Two-Stage Rocket is Used to Project a Satellite in a Circular Orbit Around a Planet

Assume that a satellite is launched from the earth's surface using a single-stage launching method. Once the rocket's fuel is ignited, the rocket begins to ascend. The rocket reaches its maximum velocity when all of the fuels have been used up.

1. The rocket escapes into space with the satellite if its maximum velocity is equal to or greater than the escape velocity, exceeding the earth's gravitational force.

2. If the rocket's greatest velocity is less than escape velocity, it will be unable to defy the earth's gravitational attraction, and both the rocket and the satellite will eventually crash to the ground.

As a result, a single-stage rocket will not be able to place a satellite into a circular orbit around the Earth. As a result, a launching device is required to place a satellite into a circular orbit around the earth.

Kepler’s law:

Kepler gave three laws of planetary motion. They are:

First law: All planets revolve in an elliptical orbit with the Sun as focus.

Second law: Irrespective of the orbit, the planet covers equal areas in equal intervals of time.

Third law: The orbital period of the planet is proportional to the orbit’s size. The cube of the mean distance of a planet from the Sun is proportional to the square of its orbital period T. r

^{3}/T^{2}=constant

Different Cases of Projection:

When a satellite is lifted to a specific height above the earth and then projected horizontally, the following four scenarios may occur, depending on the amount of horizontal velocity.

1. If the projection velocity is smaller than the critical velocity, the satellite will move in an elliptical orbit, but the point of projection will be apogee, and the spacecraft will approach the earth with its perigee point at 180o. If it enters the atmosphere as it approaches perigee, it loses energy and spirals downward. It will continue to fly in an elliptical orbit if it does not enter the atmosphere.

2.If the projected velocity achieves the critical velocity, the satellite will move in a circular orbit around the planet.

3. The satellite will be in an elliptical orbit with an apogee greater than the predicted height if the projected velocity is more than the critical velocity but less than the escape velocity.

4. The satellite goes in a parabolic path if the projection velocity is equal to the escape velocity.

5. If the projection velocity is greater than the escape velocity, the orbit will become hyperbolic, escaping the earth's gravitational attraction and continuing to travel indefinitely.

**Orbital Velocity**

Definition

The orbital velocity of a satellite is the horizontal velocity with which it must be propelled from a point above the earth's surface in order to circle in a circular orbit around the earth.

An Expression for the Critical Velocity of a Satellite Revolving Around the Earth

Assume that a mass m satellite is elevated to a height h above the earth's surface and then projected horizontally with an orbital velocity ve. The satellite starts moving around the globe in a circular orbit with a radius of R + h, where R is the earth's radius.

The gravitational force acting on the satellite is

where Mis the mass of the earth and Gis the constant of gravitation.

For circular motion,

Centrifugal force = Centripetal force

**Gravitational Field**

The space that surrounds any mass is known as a gravitational field. Any additional mass brought into this space is subjected to gravitational attraction. In a word, the area in which any mass field of gravity experiences a gravitational pull.

**Gravitational Potential**

The gravitational potential at any place in a gravitational field is defined as the work necessary to transfer a unit mass from infinity to that point.

At a distance r from a point mass M, the gravitational potential (V) is given by:

2. The potential energy of a unit mass is converted from the work done on it. As a result, the gravitational potential at any point equals the potential energy of a unit mass positioned there.

The gravitational potential energy (P.E.) of a small point mass m put in a gravitational field at a position where the gravitational potential is V is given by

Expressions for Different Energies of Satellite

1. Potential Energy (P.E.):

The satellite is at a distance (R + h) from the centre of the earth.

2. Kinetic Energy (K.E.):

The Revolution of satellites around circular orbit is having critical velocity (v_{c}). Hence its kinetic energy is given by:

3. Total Energy (T.E.):

4. Binding Energy (B.E.)

T.E. = -(B.E.)

**Escape Velocity of a Body**

Condition: The body is at rest on Earth’s surface, Escape velocity is:

The escape velocity is the smallest velocity at which a body can be launched from the earth's surface and yet escape the planet's gravitational field.

As a result, if a body or a satellite is given the escape velocity, its projection kinetic energy equals its binding energy.

Kinetic Energy of projection = Binding Energy

**Weightlessness**

1. A feeling of weightlessness is similar to a moving satellite since it alludes to the gravitational force that draws a body towards the earth's centre. It isn't due to the fact that the weight is zero.

2. A gravitational pull exerts on an astronaut when he is on the surface of the earth. This gravitational force is equal to an astronaut's weight, and an astronaut exerts this force on the earth's surface. The earth's surface produces an equal and opposite reaction, and he feels his weight on the ground as a result of this reaction.

3. An astronaut on an orbiting spacecraft experiences the same acceleration towards the earth's centre as the satellite, and this acceleration is equal to the acceleration due to the earth's gravity.

As a result, the astronaut has no impact on the satellite's floor. The astronaut, of course, is unaffected by the floor's reaction force. Because there is no reaction, the astronaut has a sense of weightlessness. (In other words, he has no concept of how heavy he is.)

**Gravity**

Gravity is the force of attraction exerted by the earth on a body lying on or near the earth's surface towards its centre. Gravity, often known as the earth's gravitational force, is a type of gravity.

The force of attraction exerted by the earth on the body towards its centre is defined as its weight. Gravitational pull or weight has the same units and measurements as a force.

**Significance of NCERT Class 11 Physics Chapter 8 Notes**

The notes for Gravitation Class 11 will help you review the chapter and have a better understanding of the main themes addressed. This NCERT Class 11 Physics chapter 8 notes are also beneficial for competitive exams such as VITEEE, BITSAT, JEE Main, NEET, and others, as they cover the main themes of the CBSE physics syllabus. You can use the Class 11 Physics chapter 8 notes pdf download to study offline.

**NCERT Class 12 Notes Chapter-Wise**

**Subject Wise NCERT Exemplar Solutions**

- NCERT Exemplar Class 11 Solutions
- NCERT Exemplar Class 11 Maths
- NCERT Exemplar Class 11 Physics
- NCERT Exemplar Class 11 Chemistry
- NCERT Exemplar Class 11 Biology

**Subject Wise NCERT Solutions**

- NCERT Solutions for Class 11 Mathematics
- NCERT Solutions for Class 11 Chemistry
- NCERT Solutions for Class 11 Physics

## Frequently Asked Question (FAQs) - Gravitation Class 11th Notes - Free NCERT Class 11 Physics Chapter 8 notes - Download PDF

**Question: **What are the primary derivations discussed in the Class 11 notes on gravitation?

**Answer: **

The NCERT notes for Class 11 Physics chapter 8 do not include any derivations. This NCERT note summarizes the chapter's important points and equations and can be used to review the gravitation.

**Question: **State the characteristics of gravitational force.

**Answer: **

In Class 11 Physics chapter 8 notes When two masses are separated by a certain distance, they are attracted to one other. The gravitational force is the name for this force. In Class 11, three important features of the gravitational pull are discussed. Because the force exists between the two particles and is independent of the medium that separates them, it is long-ranged in nature. Force and distance, for example, have an inversely proportionate connection. In nature, this power is enticing.

**Question: **What is escape velocity?

**Answer: **

According to Gravitation Class 11 notes pdf download the minimal speed necessary by a non-propellant object to escape the Earth's gravitational influence is known as escape velocity.

The escape velocity (Ve) on Earth's surface is 11.2 km/s (this speed is 33 times the speed of sound).

**Question: **State the Difference Between Mass and Weight.

**Answer: **

The mass of an object according to Class 11 Gravitation notes is the amount of matter it contains, whereas its weight is the measure of the force exerted on it by gravity or the amount of gravitational attraction it experiences

**Question: **What is Gravitational Potential?

**Answer: **

In Class 11 Physics chapter 8 notes the amount of work required to transport a unit mass from infinity to that location without acceleration is the gravitational potential at that place.

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