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GRAVITATION, , --> Gravitation:- Force of attraction between any two Objects of the universe is called gravitation or, gravitational force., , --> Gravity:- Force of attraction between earth and an object ts called gravity., , --> Gravity is a special case of gravitation in which one of the two object fs earth., , , , , , , he earth and an object Is called ' earth's gravity’, , *UNIVERSAL LAW OF GRAVITATION OR NEWTON LAW OF GRAVITATION*, , --> It was given by Newton so, it is also called Newton law of gravitation., , Ans:- The gravitational force betw, , , , --> Itis an universal law because it is applicable to all the bodies having masses whether they are terristrial or, celestial. Further they are of any shape, size or mass and they may be any distance apart with any medium, between them., , --> According to the universal law of gravitation, every body in the universe attracts every other body witha, force which is directly proportional to the product of their masses and inversely proportional to the square of, the distance between them. The direction of force is along the line joining the centre of two bodies., , , , Q Whatis the importance of tiniversal la, , : ees: z, , Ans:- The importance of universal law of gravitation is that it explains the motion of planets around the sun; the, motion of moon around the earth; the motion of artificial satellites around the earth. It also explain the, phenomena of rainfall, snowfall and flow of water in river on the earth, formation of tides., , , , ** MATHEMATICAL EXPRESSION OF GRAVITATIONAL FORCE** =, --> Suppose two bodies A and B of masses m1 and mz LRN 8, , are lying at a distance “d” from each other. ( © \ °, , Let the force of attraction between these two bodies be F. \ na 4 Mo, , Now, according to the universal law of gravitation ——— _ 4d, , The force between two bodies is directly proportional to the product of their masses, Foy & Mg wnreererereeee (i), , The force between two bodies is inversely proportional to the square of distance between them, , On combining (i) and (ii) we get, , Fa,, d*, , , , , , “ey,, , Fa Q, , , , , a, , , , Scanned with CamScanner
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Where ‘Gis a constant known as universal gravitational constant., --> When an object is placed on or near the surface of earth, then the distance between them is taken as radius ofearth. In this case £, , O < Object @, , , , Garth, M=Mass of earth, m= Mass of object., , R= Radius of Earth, , , , Q Write the formula'to find the magn, surface of the earth.[N.C.E.R. T], , , , dé of thie gravitational force between the carina, , , , Ans:- Gravitational force, F= Gx Mxm/R?, : . ., Where, G= Gravitational constant, , Mz= Mass of the earth., , m= mass of the object., , And R= Radius of the earth, **UNIVERSAL GRAVITATIONAL CONSTANT**, , --> We know that, , Fz & mM, Mo, , , , , , , , =, La m= KA, Ms Tk, ge tm then, f= rl é, , f *, , [Fea], , --> Universal gravitational constant(G) is a force of attraction that exist between two bodies of unit mass, separated by unit distance,, , --> We know that, , , , Fe G ape a, NAO, 7G: exg? (ad q@= NAD %, A, KM, 3°, , Therefore, SI unit of G is Nm*/kg?., --> The value of G is 6.67 X 10°Nm?/kg’. It was calculated by Henary Cavandish., , --> Since G is constant So, its value is independent of mass, shape, size, distance and medium betweentwo «, , 17, 2, , Scanned with CamScanner
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objects., , *KEPLER LAW OF PLANETARY MOTION, , --> Kepler has given three laws of planetary motion which govern the motion of planets., , pier sy, , , , *" euictéal orbt, , , , nae enee, , Figure 18, Divgram for Kepler's first Law, fof planetary motion, , Second law (Law of areas ), , Each planet revolves around the sun in such a way that the line joining the planet to the sun sweeps over equal *, areas in equal intervals of time. A planet moves faster when it is closer to the sun and moves slowly when it is, farther from the sun:, , , , Third law (Law of periods ), , The cube of mean distance of a planet from the sun is directly proportional to the square of the time it takes to, move around the sun, , , , where, a= meon distance of planet From Sun, T= Time period oF planed (around sun)., Q: What happens to the force bei objects, if[NCERT], , i, , N, , First law (Law of orbit ), , The planets move in elliptical orbits around the sun, with the sun at one of the two foci of the elliptical orbit., t, a, , , , | %, (i) the mass of one object is doubled, , , , Fray, , (ii) the distance between object is double, , , , , (iii) the distance between the ol, (iv) the masses of both objects ar, , Ans:, Scanned with CamScanner
