Presentation on theme: "BHORANIYA AHEMAD ABBAS A."— Presentation transcript:
1BHORANIYA AHEMAD ABBAS A. FRICTION AND ITS TYPESBYBHORANIYA AHEMAD ABBAS A.( )
2What is Friction Friction is a force A frictional force can exist when two substances contact each other.The molecules of each surface interact according to Newton’s Laws of Motion.Friction always opposes motion, i.e., it is opposite to the direction of velocity.If there is no motion, then friction opposes the sum of all the other forces which are parallel to the surfaces in contact.
3Friction ForceWhen an object is in contact with a surface there is a force acting on that object. The component of this force that is parallel to the surface is called the friction force.This resistive force is exerted on a moving object due toviscosity or other types of frictional property of the medium in or surface on which the object moves.Always opposite to the movement!!3
4Contact ForceForce that occurs between objects that are in contact with each other.Contact forces can be resolved into components that are perpendicular and parallel to the surfaces in contact.The perpendicular component is called the normal force.The parallel component is called friction.
5Contact Force in Running Resultant force on runnerrunner’s pushNormal ForceFriction ForceDuring the push off phase in running, the normal force acts upward on the runner, while the friction force acts forward on the runner. The friction force is the only force capable of moving the runner horizontally down the track. The normal force can only accelerate the runner upwards.
6Friction and the Normal Force The maximum frictional force is proportional to the normal contact force.An increase in the normal force results in an increase in the maximum friction.This is because the molecules on the two surfaces are pushed together more, thus increasing their interactions.
7“Normal” Forces and Frictional Forces 4/18/2008“Normal” Forces and Frictional Forces“Normal” meansperpendicularReaction ForceFrom RampNormalForceFrictionDecompose VectorWeight of blockWeight of blockFriction Force = Normal Force (coefficient of friction)Ffriction = FnormalLecture 8
8Friction and Surface Area Friction is not affected by the size of the surface area in contact.If the normal force remains constant, but the contacting surface area is increased, then the normal force is spread out over more molecules, thus the force on each molecule is reduced.Amontons (1699)What about race car tires?
9Calculating Friction Ff_max = FN Ff_max is the maximum force of friction (Mu) is the coefficient of frictionFN is the normal forceFriction can range in value from -Ff_max to +Ff_max depends on the types of surfaces that are interacting. It would be low for rubber on ice, but high for rubber on asphalt. It also depends on whether the surfaces are moving relative to each other ( static or dynamic )4/15/2017Dr. Sasho MacKenzie - HK 376
10> Types of Friction Dry Friction Fluid Friction Static Friction Occurs with fluids,or lubricated surfacesDry FrictionOccurs between the non-lubricated surfaces of solid objectsStatic FrictionWhen dry friction acts between two surfaces that are not moving relative to each otherDynamic FrictionWhen dry friction acts between two surfaces that are moving relative to each other>4/15/2017Dr. Sasho MacKenzie - HK 376
11Static Frictionthe force exerted on a stationary object by a surface that prevents the object from starting to move (Fs)the object remains at rest because the static friction is equal in magnitude and opposite in direction to the applied forcefor the object to move, the applied force must overcome the maximum amount of static friction (Fsmax)
12The Force of Static Friction keeps a stationary object at rest! FNFfsFg
13Types of Kinetic Friction sliding friction : an object is scraping or sliding across a surfacerolling friction : an object rolls across a surfacefluid friction or air resistance : an object travels through water or air and experiences drag
14Kinetic FrictionOnce the Force of Static Friction is overcome, the Force of Kinetic Friction is what slows down a moving object!MotionFNFfkFg
15Kinetic or Dynamic Friction the force exerted on a moving object by a surface (Fk)acts in the opposite direction of the motionif applied force is equal in magnitude to the force of friction, the object will move with a constant velocityif the applied force increases, the object will accelerate
16“Fluid” FrictionThis type of friction is what happens with liquids and gases (In Physics, liquids and gases are both called "fluids". They behave in similar ways.)Fluid friction is also known as "drag". On aircraft it's also called "air resistance". It depends on:-how thick the fluid is (its "viscosity")the shape of the objectthe speed of the object
17Coefficient of friction Normal force (N)Ff = m FnFriction force (N)Coefficient of friction