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HEMANT BHARDWAJ

Rolling friction is the friction force acting on a body which is rolling on a surface.

in pure uniform rolling when V=RW (here W is angular speed) and acceleration is zero friction force will be also zero since body does not have tendency to RUB the surface or in other word the relative velocity of lower most point will be zero w.r.t ground.

on the other hand if V>RW then the lowermost surface will be rubbing surface in forward direction and hence friction will act backward.

IF V<RW then body will exert force(rub) in backward direction on ground and hence friction will act in forward direction

(ALWAYZ REMEMBER THAT FRICTION ALWAYS TRY TO STABLISH SITIUATION V=RW IF V>RW THEN FRICTION ACTS BACKWARD IN ORDER TO REDUCE LINEAR VELOCITY AND INCREASE ANGULAR VELOCITY(BY PRODUCING SOME TORQUE) and vice versa

if rolling body is rolling without slipping but has some acceleration coz of some external force then friction always act in opposite direction as that of external force

(for example if a body is moving either up or down on a inclined plane then froction alwayz act in upward direction coz external force=mgsinx alwayz act downward)