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body placed on an inclined plane just begin to, 1 on an inclined plane. Let 0 be the angle of, , , , , , , , From figure, tan 0 =, , , , , , Angle of repo:, , It is the minimum angle with which the, move Consider a body of mass m place, repose.The various forces acting on the body are, 1 the weight mg acting vertically downward, , 2 the normal reaction R vertically upwards and, , , , , , gentially upward to inclined plane, , 3 the frictional force fs tan,, in 0 and mg cos 0, , Resolving mg, we get mg, From figure , mg sin 0 = fs and mg cos 0= R, iganee fs/R = jt thus tangent of the angle of repose is equal to the coefficient of static, Advantages of fri, 1) Ithelps us to walk on road., 2) Ithelps to holt an object., 3) Ithelps to light a matchstick., Disadvantages or, 1) It decreases the efficiency of the engine., 2) It causes wear and tear of the moving parts of the machine., , 3) The friction i: air reduces the speed of the vehicle., A lubricant is substance which forms a thin layer between two surfaces in, , Lubrication;, contact.It fills depression present on the surfaces of contact and hence friction is, reduced.Generally oils and grease are used as lubricants.The application of lubricanta at, , , , , , , , , , , , , , , , the joints is called lubrication., , Uniform circular motion:, , ‘An object which moves on a circular path with a constant speed is said to be in uniforrn, , circular motion., , Period;- It is the time taken by an object for one complete revolution.(T), , Frequency:- It is the number of revolutions made by an object in one second., f=1/ T, Unit - hertz (Hz) or cycles/s or revolutions/s., , Angular displacement (0) - It ig the angle swept by the radius, , vector ina given time., Consider an object moving ina circular path of radius r with, Uniform speed v.lna time t let the position of the changes from A to B.|Now angular, , , , , , are AB / Radius, , acement is radian. Also it is vector quantity. Its direction is, It states that if the curvature of the fingers of the right hand, an the thnab represents the direction of angular displacement, rate of change of angular displacement. 0 is the, =0//t. Itis a vector quantity having the same, , displacement, 0 =, The SI unit of angular displ, given by right hand grip rule., represents the sense of rotation th, Angular velocity (o):- It i the time, acement ina time tthen @, , angular displ., : isplacement.lts SI unit is rad/s., , Sines tion as that of the angular di