Gravitation

• 1. 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 Keplers Law of Planetary motion

2. The rotation of the earth around the sun or that of the moonaround earth is explained on the basis of this law. The tide are formed in ocean due to the gravitationalforce of attraction between earth and the moon. The value of g can be used to predict the orbits and timeperiod of an satellite.Attraction Force between two bodies 3. The Gravitation force between two masses is independentof the intervening medium. The mutual gravitational forces between two bodies areequal and opposite i.e. Gravitational Forces obey Newtonsthird 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 acentral force. Its magnitude depends only on r and has noangular dependence . The Gravitational force between two bodies is independentof the presence of other bodies. 4. Consider an Elevator freely falling from North pole toSouth pole through the center of earth. Describe itsmotion?? For answer Press Enter .. 5. 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. 6. Gravitational field Gravitational field . Two bodies attract each other by thegravitational force even if they are not in direct contact. Thisinteraction is called action at a distance. It can bestexplained in terms of concept of field. According to the fieldconcept. Every mass modifies the space around it . This modified space is calledgravitational field When any other mass is placed in this field , it feels a gravitational force ofattraction due to its interaction with the gravitational field The space surrounding a material body within which itsgravitational force of attraction can be experiences a force ofattraction towards the centre of earth 7. Gravitational Potential EnergyA dxBPxrRO 8. If we throw a ball into air , it rises to a certain height and fallsback. If we throw it with a greater velocity , it will rise higherbefore falling down. If we throw with sufficient velocity , it willnever come back . i.e. It will escape from the gravitational pulof 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 Rwith centre O. 9. Can you tell why moon has no atmosphere ?? For answer press enter Due to the small value of g. The escape velocity in themoon is 2.38 km/s . The air molecules have thermal velocityis greater than the escape velocity and therefore airmolecules escape. 10. SatelliteArtificial NaturalGeostationary Polar 11. Satellite is an body which continuously revolves on it ownaround and a much larger body in a stable orbit. Natural satellites : A satellite created by nature is callednatural satellite . example : moon. Artificial satellite : A man made satellite is called an artificialsatellite. Example Chandrayaan . Worlds Frist satellite was SPUTNIK-1. 12. Principle for launching a satellite : Consider a high towerwith its top projecting outside the earths atmosphere. Lets throw a body horizontally from the top of the tower withdifferent velocities. As we increase the velocity of horizontal projection , thebody will hit the ground at point farther and farther from thefoot of the tower. At certain velocity the body will not hit the ground , butalways be in a state of free fall under the influence of thegravity. Then the body will follow a stable circular orbit . And thatbody is called satellite. 13. Click on the video 14. Orbital velocity is the velocity required to putthe satellite into its orbit around earth 15. VoR R+h h 16. A satellite which revolves around the earth in tis equatorialplane with the same angular speed and in the samedirection as the earth rotates about its own axis is called ageostationary or synchronous satellite. 17. It should revolve in an orbit concentric and coplanar withthe 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 exactlysame as that of the earth about its own axis , i.e 24 hours It should revolve at a height of exactly 35930 km. 18. In communicating radio,T.V and telephone signals acrossthe 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). 19. A satellite that revolves in a planar orbit is called a polarsatellite. Eg IERS (Indian earth resources satellites) Uses of Polar satellite Polar satellites are used in weather and environment monitoring. Spying Study topography of other celestialbodies 20. Law of orbits (first law) : Each planet revolves around thesun in an elliptical orbit with the sun situated at the one ofthe two foci. 21. Law of areas (second law) : The radius vector drawn fromthe sun to a planet sweeps out equal areas in equalintervals of time i.e the areal velocity ( area covered perunit time) of a planet around the sun is constant. 22. P planetsun