Ans: According to the law of gravitation:

The force of attraction between two material bodies is directiy proportional to

the product their masses (m and m2) and inversely proportional to the square of

the distance (r) between them."

mm2Mathematically, FocrGm m2

orF=Hereisknownas"Gravitationalconstant". The value G is 6.67x10NkgThe force of attraction between any two bodies is called 'gravítation If one of the bocy is the earth, then the force of attraction between the earth and any other materialobjectiscalled"forceofgravity"orsimplygravity(i.e.weight).GRAVITATIONAL FORCE:Q.2: Write three characteristics ofgravitational force.Ans: (1) The gravitational force acting on two material bodies forms an action

reaction 'pair of forces.(2) It is "action-at-a-distance" force.(3) This attractive force obeys inverse square law, i.e. force(distance)Write the law of gravitation in vector form.The gravitational force is a force of attraction; and it is a vector quantity() The force on body A by the body B is

- G U mATBAATBAFAB =Where rBA is the distance of the body A from the body B

FARF BAFig. 6.1Gi)The force on body B by the body A is

FBA =- G A MgTABTABWhere rAB is the distance of the body B from the body A.Thus, FAB -FBAHE VALUE OF'g' AT HEIGHTS:: How does

How does the value of 'g' decrease if we go up a distance RSRabove the surface of the earth?t

Where rA is the distance of the body B from the body A.Thus, FAB =- FBA

THE VALUE OF g' AT HEIGHTS:How does the value of 'g' decrease if we go up a dista

3Re above the surface of the earth?GMe

Ans.: We known, g =Re

Here Me and Re refer to the mass and radius of the earth.

If we go up a distance Re from the surface of the earth (i.e

total distance from the center of the earth is 2 Re), then 'g'

decreases to g/4.(i)

If we go up a distance 2 Re (i.e. total distance is 3R.), then g

decreases to g/9.

If we go up a distar.ce 3 Re (i.e. total distance is 4 R), then g

decreases to g/16.