LAWS OF FRICTION LAWS OF MOTION LAWS OF
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LAWS OF FRICTION LAWS OF MOTION
LAWS OF FRICTION
LAWS OF FRICTION Laws of friction Ø Leonardo Da Vinci conducted a number of experiments and studied the motion of bodies on horizontal planes and inclined planes. Ø He proposed the rules governing the motion under friction as laws of friction.
LAWS OF FRICTION 1. The frictional force between the body and the surface is independent of the area of contact 2. Frictional force is always directly proportional to the normal reaction Both these laws are applicable to Static as well as Kinetic friction.
LAWS OF FRICTION If ‘N’ is the normal reaction, then the frictional force is given by f N or f = N = Co-efficient of friction v It is defined as the ratio of frictional force and normal reaction.
LAWS OF FRICTION Ø It has no units and dimensions. It can be determined experimentally. Ø It depends upon molecular nature of the surfaces in contact and their smoothness. Ø Dust and impurities on the surface drastically affect the value of frictional force and hence the co-efficient of friction.
LAWS OF FRICTION MCQ S 1) The friction between two surfaces in contact is independent of …. a) nature of surfaces in contact b) normal reaction between the surfaces c) area of surfaces in contact d) all the above
LAWS OF FRICTION 2) Normal reaction depends only on the …. . a) nature of contact b) area of contact c) both (a) & (b) d) none of these
LAWS OF FRICTION 3) Frictional force is always a) inversely proportional b) directly proportional c) equal d) none of these to the normal reaction
LAWS OF FRICTION 4) The co-efficient of friction a) has only units b) has only dimensions c) has units and dimensions d) does not have units and dimensions .
LAWS OF FRICTION LAWS OF STATIC FRICTION
LAWS OF FRICTION Laws of static friction Ø Limiting friction is independent of the area of contact, so long as the normal reaction remains the same. Ø Limiting friction depends on the materials of the surfaces in contact and their state of polish. Ø The limiting friction is directly proportional to the magnitude of normal reaction between the two surfaces. Where s = co-efficient of static frictional force f. L = limiting frictional force N = normal reaction
LAWS OF FRICTION v The static frictional force fs � s. N when the bodies do not slide over each other.
LAWS OF FRICTION 1) The coefficient of static friction is…. . a) The ratio of normal force to the limiting friction b) The ratio of tangential force to the limiting friction c) The ratio of limiting friction to the normal force d) none of these MCQ S
LAWS OF FRICTION LAWS OF KINETIC AND ROLLING FRICTION
LAWS OF FRICTION LAWS OF KINETIC FRICTION: Ø Kinetic frictional force is directly proportional to normal reaction. Ø It is independent of area of contact as long as magnitude of normal reaction remains the same. Ø Kinetic friction is almost independent of velocity, provided the velocity is not too large or not too small.
LAWS OF FRICTION Laws of rolling friction Ø The rolling friction is directly proportional to the normal reaction. Ø It depends on the area of contact. Ø If the area of contact is small, the rolling friction is less. Ø If the radius of the rolling body is more, then it possesses less rolling friction. Ø The co-efficient of rolling friction is the ratio of rolling frictional force to the normal reaction.
LAWS OF FRICTION Ø Let fr be the rolling frictional force and N be the normal reaction the co-efficient of rolling friction. Note : Ø For similar surfaces the co-efficient of rolling friction ( r) is smaller than the co-efficient of kinetic friction ( k). r < k
LAWS OF FRICTION 1) When a body is moving with we can apply laws of kinetic friction. a) more b) less c) equal d) greater than or equal to MCQ S velocity then
LAWS OF FRICTION 2) The co-efficient of kinetic friction is the ratio of kinetic frictional force to the of a body. a) normal reaction b) tangential force c) parallel force d) none of these
LAWS OF FRICTION 3) Rolling friction is to the normal force a) inversely proportional b) directly proportional c) equal d) greater
LAWS OF FRICTION 4) For same surfaces the co-efficient of rolling friction r is much _____ than co-efficient of kinetic friction k. a) smaller b) greater c) equal d) greater than equal to
LAWS OF FRICTION Thank you…
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