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FRICTION AND ITS TYPES BY BHORANIYA AHEMAD ABBAS A. (130460106008)

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Presentation on theme: "FRICTION AND ITS TYPES BY BHORANIYA AHEMAD ABBAS A. (130460106008)"— Presentation transcript:

1 FRICTION AND ITS TYPES BY BHORANIYA AHEMAD ABBAS A. ( )

2 2 What is Friction Friction is a forceFriction is a force A frictional force can exist when two substances contact each other.A frictional force can exist when two substances contact each other. The molecules of each surface interact according to Newton’s Laws of Motion.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.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.If there is no motion, then friction opposes the sum of all the other forces which are parallel to the surfaces in contact.

3 When 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. Friction Force This resistive force is exerted on a moving object due to Always opposite to the movement!! viscosity or other types of frictional property of the medium in or surface on which the object moves.

4 4 Contact Force Force that occurs between objects that are in contact with each other.Force 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.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 perpendicular component is called the normal force. The parallel component is called friction.The parallel component is called friction.

5 5 Contact Force in Running Normal Force Friction Force During 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. runner’s pushResultant force on runner

6 6 Friction and the Normal Force The maximum frictional force is proportional to the normal contact 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.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.This is because the molecules on the two surfaces are pushed together more, thus increasing their interactions.

7 “Normal” Forces and Frictional Forces Weight of block Decompose Vector Normal Force Friction Force Weight of block Reaction Force From Ramp “Normal” means perpendicular Friction Force = Normal Force  (coefficient of friction) F friction =  F normal

8 8 Friction and Surface Area Friction is not affected by the size of the surface area in contact.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.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?What about race car tires?

9 5/10/2015Dr. Sasho MacKenzie - HK 3769 Calculating Friction F f_max =  F NF f_max =  F N F f_max is the maximum force of friction  (Mu) is the coefficient of friction F N is the normal force Friction can range in value from -F f_max to +F f_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 )

10 5/10/2015Dr. Sasho MacKenzie - HK Types of Friction Dry Friction Occurs between the non-lubricated surfaces of solid objects Fluid Friction Occurs with fluids,or lubricated surfaces Dynamic Friction When dry friction acts between two surfaces that are moving relative to each other > Static Friction When dry friction acts between two surfaces that are not moving relative to each other

11 Static Friction  the force exerted on a stationary object by a surface that prevents the object from starting to move (F s )  the object remains at rest because the static friction is equal in magnitude and opposite in direction to the applied force  for the object to move, the applied force must overcome the maximum amount of static friction (F s max )

12 Static Friction FNFN fsfs F FgFg The Force of Static Friction keeps a stationary object at rest!

13 Types of Kinetic Friction  sliding friction : an object is scraping or sliding across a surface  rolling friction : an object rolls across a surface  fluid friction or air resistance : an object travels through water or air and experiences drag

14 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

15 Kinetic or Dynamic Friction  the force exerted on a moving object by a surface (F k )  acts in the opposite direction of the motion  if applied force is equal in magnitude to the force of friction, the object will move with a constant velocity  if the applied force increases, the object will accelerate

16 “Fluid” Friction This 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 object the speed of the object

17 Friction Friction F f =  F n Normal force (N) Coefficient of friction Friction force (N)

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