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# Gravitational Motion - Physics - General Test Preparation for CUET

 Table of contents Solar system Kepler’s laws Newton’s Universal Law of Gravitation Acceleration Due to Gravity Variation in the Value of G With Height Geostationary Satellites

## Solar system

• It consists of sun which is stationary at the centre of the universe, a source of light and energy and eight planets (Pluto has lost it planet status) which revolve around the sun in separate orbits.
• The order of the planets in the solar system with their increasing distance from the sun is-
• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune

The Solar System

• John kepler found important regularities in the motions of the planets.
• He gives three law in this context called kepler’s laws of planetary motion.

## Kepler’s laws

1. all planets move around the sun in elliptical orbits having the sun at one force of the orbits.
2. The Areal speed of the planet remains constant.
3. The square of the period of revolution of any planet around the sun is directly proportional to the cube of its mean distance from the sun, i.e.,
• T2 or r3

## Newton’s Universal Law of Gravitation

• Every two objects in the universe attract each other.
• “The force of attraction is directly proportional to the product of masses and inversely proportional to the square of the distance between the two masses”
• F ∞ mm 2 / r²
(or) F = G . m 1 m 2 / r²
• where, G = universal gravitational constant.
• G = 6.67 x 10 -11 N m -2 kg -2

## Acceleration Due to Gravity

• When a body falls freely, then the increase in velocity per second is called acceleration due to gravity.
• It is represented by g.
• g = GMe / Re²
• where, Me = mass of the earth,
• Re = radius of the earth.
• Value of g depends upon the radius of the earth as g ∞ 1 / R.
• So, value of g is maximum at poles and minimum at equator.

## Variation in the Value of G With Height

• Value of g at the surface of the earth is 9.8 m / s²
• Value of g at the centre of earth is zero.
• Value of g at infinity becomes zero.
• If the body is taken inside the earth, acceleration due to gravity decreases linearly with the distance from centre of the earth.
• If the body is taken above the surface of the earth, acceleration due to gravity varies inversely as the square of the distance from the centre of earth.
• g is a vector quantity. Its direction is towards the centre of the earth.
• Its value is independent of the shape, size, mass, etc of the body but depends upon mass and radius of the earth or planet due to which there is a gravity pull.

## Geostationary Satellites

• Geostationary satellites are stationary with respect to an observer on the earth.
• Their time period is 24 hrs. Their height above the surface of earth is 36,000 km.
• They are always in equatorial plane and their orbits are circular. They are also called parking orbits.
• the speed of satellite depends upon its height from the earth’s surface. The farther is the satellite from the earth’s surface, the lesser will be its speed.
• The velocity of a satellite does not depend upon its mass. There force, if various satellites of different masses revolve around the earth in same orbit then orbital velocities will be the same.

Motion of Geostationary Satellites

• In an artificial satellite reaction of a person is zero; therefore the person does not experience any weight. This state is known as the state of weightlessness.

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## General Test Preparation for CUET

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## FAQs on Gravitational Motion - Physics - General Test Preparation for CUET

 1. What is the solar system?
Ans. The solar system refers to a collection of celestial bodies, including the sun, planets, moons, asteroids, comets, and other smaller objects, all held together by the sun's gravitational force. It is located in the Milky Way galaxy and is our home within the vast universe.
 2. What are Kepler's laws?
Ans. Kepler's laws are three fundamental principles that describe the motion of planets and other objects in the solar system. They were formulated by the German astronomer Johannes Kepler in the early 17th century. Kepler's laws state that planets move in elliptical orbits around the sun, that the line connecting a planet to the sun sweeps out equal areas in equal times, and that the square of a planet's orbital period is proportional to the cube of its average distance from the sun.
 3. What is Newton's Universal Law of Gravitation?
Ans. Newton's Universal Law of Gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This law explains the gravitational force that holds objects in the solar system together, as well as the motion of planets and other celestial bodies.
 4. What is the acceleration due to gravity?
Ans. The acceleration due to gravity, denoted as "g," is the acceleration experienced by an object in free fall near the surface of a planet or other celestial body. On Earth, the average value of g is approximately 9.8 meters per second squared (m/s²), meaning that every second an object falls, its velocity increases by 9.8 m/s.
 5. How does the value of g vary with height?
Ans. The value of g decreases with an increase in height above the surface of a planet or a celestial body. This is because the gravitational force weakens as the distance between two objects increases. Therefore, the acceleration due to gravity, g, decreases as an object moves higher above the surface. However, this decrease is very gradual and is usually negligible within small height differences on Earth.

## General Test Preparation for CUET

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