• Definition for Gravitation• Acceleration Due to Gravity• Variation Of “G” With Respect to Height And Depth• Escape Velocity• Orbital Velocity• Gravitational Potential• Time period of a Satellite• Height of Satellite• Binding Energy• Various Types of Satellite• Kepler’s Law of Planetary motion
• The rotation of the earth around the sun or that of the moon around earth is explained on the basis of this law.• The tide are formed in ocean due to the gravitational force of attraction between earth and the moon.• The value of g can be used to predict the orbits and time period of an satellite. Attraction Force between two bodies
• The Gravitation force between two masses is independent of the intervening medium.• The mutual gravitational forces between two bodies are equal and opposite i.e. Gravitational Forces obey Newton’s third law of motion.• The gravitational force is an conservative force.• The law of gravitation holds only for point masses.• The gravitational force between two point masses is a central force. Its magnitude depends only on r and has no angular dependence .• The Gravitational force between two bodies is independent of the presence of other bodies.
• Consider an Elevator freely falling from North pole to South pole through the center of earth. Describe its motion??• For answer Press Enter ..
The Variation of g with respect to Depth and Height(graph). The Variation of g with respect to height will never bezero. It will increase after certain height. The Variation of g with respect to depth will be zerowhen the body is placed at the center of earth.
Gravitational field• Gravitational field . Two bodies attract each other by the gravitational force even if they are not in direct contact. This interaction is called action at a distance. It can best explained in terms of concept of field. According to the field concept. – Every mass modifies the space around it . This modified space is called gravitational field – When any other mass is placed in this field , it feels a gravitational force of attraction due to its interaction with the gravitational field• The space surrounding a material body within which its gravitational force of attraction can be experiences a force of attraction towards the centre of earth
Gravitational Potential Energy A dx B P x r R O
• If we throw a ball into air , it rises to a certain height and falls back. If we throw it with a greater velocity , it will rise higher before falling down. If we throw with sufficient velocity , it will never come back . i.e. It will escape from the gravitational pul of the earth.• The minimum velocity required to do so is called escape velocity.• Consider the earth to be a sphere of mass M and radius R with centre O.
• Can you tell why moon has no atmosphere ??• For answer press enter• Due to the small value of g. The escape velocity in the moon is 2.38 km/s . The air molecules have thermal velocity is greater than the escape velocity and therefore air molecules escape.
• Satellite is an body which continuously revolves on it own around and a much larger body in a stable orbit.• Natural satellites : A satellite created by nature is called natural satellite . example : moon.• Artificial satellite : A man made satellite is called an artificial satellite. Example Chandrayaan .• World’s Frist satellite was SPUTNIK-1.
• Principle for launching a satellite : Consider a high tower with its top projecting outside the earth’s atmosphere.• Lets throw a body horizontally from the top of the tower with different velocities.• As we increase the velocity of horizontal projection , the body will hit the ground at point farther and farther from the foot of the tower.• At certain velocity the body will not hit the ground , but always be in a state of free fall under the influence of the gravity.• Then the body will follow a stable circular orbit . And that body is called satellite.
• A satellite which revolves around the earth in tis equatorial plane with the same angular speed and in the same direction as the earth rotates about its own axis is called a geostationary or synchronous satellite.
• It should revolve in an orbit concentric and coplanar with the equatorial plane of the earth.• Its sense of rotation should be same as that of the earth , i.e From west to east.• Its period of revolution around the earth should be exactly same as that of the earth about its own axis , i.e 24 hours• It should revolve at a height of exactly 35930 km.
• In communicating radio,T.V and telephone signals across the world.• In studying the upper regions of the atmosphere.• In Forecasting weather.• In studying meteorites.• In studying solar radiation and cosmic rays.• And used in GPS (Global positioning System).
• A satellite that revolves in a planar orbit is called a polar satellite. Eg IERS (Indian earth resources satellites)• Uses of Polar satellite – Polar satellites are used in weather and environment monitoring. – Spying – Study topography of other celestial bodies
• Law of orbits (first law) : Each planet revolves around the sun in an elliptical orbit with the sun situated at the one of the two foci.
• Law of areas (second law) : The radius vector drawn from the sun to a planet sweeps out equal areas in equal intervals of time i.e the areal velocity ( area covered per unit time) of a planet around the sun is constant.