S. M. Dhawade Department of Civil Engineering PRMCEAM, Badnera

Topic :- Friction Hard to Live With It, Can’t Live Without It What’s Stopping You?

What is Friction? Force that acts oppose the relative motion of two surfacesForce that acts oppose the relative motion of two surfaces High for dry and rough surfacesHigh for dry and rough surfaces Low for smooth and wet surfacesLow for smooth and wet surfaces

Laws of friction The force of friction always acts in direction opposite toThe force of friction always acts in direction opposite to that in which body tends to move Till the limiting value is reached,the magnitude of friction exactly equals to the applied forceTill the limiting value is reached,the magnitude of friction exactly equals to the applied force The magnitude of limiting friction bears a constant ratio to the normal reaction between the two surface of contact and this ratio is called coefficient of frictionThe magnitude of limiting friction bears a constant ratio to the normal reaction between the two surface of contact and this ratio is called coefficient of friction The force of friction depends upon the smoothness and roughness of the surfaceThe force of friction depends upon the smoothness and roughness of the surface The force of friction is independent of the area of contact between the two surfacesThe force of friction is independent of the area of contact between the two surfaces

Free Body Diagram Normal Force F N Friction Force f f Applied Force F Gravity Force F g F g = mg F N = F g f f = F

Types of Friction Static Friction Static FrictionStatic FrictionStatic Friction Force that does not cause the object to moveForce that does not cause the object to move Sliding Friction Sliding Friction Sliding Friction Sliding Friction Very effective at opposing the movement of objectsVery effective at opposing the movement of objects Rolling Friction Rolling Friction Less than the force of sliding frictionLess than the force of sliding friction Fluid Friction Opposes the motion of objects traveling through a fluidOpposes the motion of objects traveling through a fluid

What is static friction? From Glencoe Physical Science Static friction is friction between two surfaces which are not moving Past each other IF you were trying to a push a box shown in pictured and the IF box did not move,this would be static friction FNFN fsfs F FgFg For Example :- Static friction = Fs = Us x F N

Kinetic Friction FNFN fkfk F FgFg Once the Force of Static Friction is overcome, the Force of Kinetic Friction is what slows down a moving object! Motion Graph Shows

What is sliding friction? Sliding friction occurs when a force is great enough to overcome the static friction.Sliding friction occurs when a force is great enough to overcome the static friction. Glencoe Physical Science What is rolling friction? Rolling friction is the friction which enables wheels to turn and objects to move. If there were no friction, turning wheels would not enable an object to move.

Advantage and disadvantage of friction The soles of shoesThe soles of shoes Car tiresCar tires The feet of table legsThe feet of table legs Rock climbing holdsRock climbing holds BrakesBrakes In engines In transmissions On the bottoms of skis and snowboards (To a point) When you are trying to move a box by pushing it along the floor Advantage Disadvantage

Types of Friction shown with picture I better be safe Ump!! To initiate motion of the box the man must overcome the Force of Static Friction Upon sliding, the baseball player will come to a complete stop due to the Force of Kinetic Friction

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Static & Kinetic Friction Coefficients MaterialCoefficient of Static Friction  S Coefficient of Kinetic Friction  S Rubber on Glass Rubber on Concrete Steel on Steel Wood on Wood0.25 – Metal on Metal Ice on Ice Synovial Joints in Humans