FRICTION

Friction is a force that opposes motion betweentwo surfaces that touch each other.

2.FORCE OF FRICTION

Force of friction is the force which opposes the motion of an object over a surface.The force of friction acts between the object and the surface.

Eg :- A ball rolling on ground gradually slows down and comes to rest due to force of friction between the ball and the ground.

If we stop pedalling a bicycle, it gradually slows down and comes to a stop due to force of friction between the wheel and the road.

3.FACTORS AFFECTING FRICTIONFriction depends upon two factors. They are :-

i) Nature of the surfaces in contact. ( The smoothness of the surfaces).

Ii) How hard the surfaces press together. Friction is less on a smooth surface Friction is more on a rough surface.

Friction is more if the surfaces arepressed harder…………….?

Friction is less if the surfaces arenot pressed harder…………..?

4.CAUSE OF FRICTIONFriction is caused due to the interlocking of irregularities between the two surfaces in contact.

Smooth surfaces have minute irregularities between the two surfaces.

Rough surfaces have larger irregularities between the two surfaces.So force of friction is more if the surfaces are rough.

5. TYPES OF FRICTIONThere are two kinds of friction: static frictionand kinetic friction:Static friction is the force between two stationary objects.static friction is always greater than kinetic friction.Static friction prevents an object from moving against asurface. It is the force that keeps a book from slidingoff a desk, even when the desk is slightly tilted, and thatallows you to pick up an object without the object slippingthrough your fingers.In order to move something, you must first overcome theforce of static friction between the object and thesurface on which it is resting.There are three main types of friction. They are static friction,sliding friction and rolling friction.a) Static friction is the friction exerted on a object at rest. .b) Sliding friction is the friction exerted when an object slides over a surface.

c) Rolling friction is the friction exerted when an object rolls over a surface.Sliding friction is slightly less than static friction.Rolling friction is less than sliding friction and static friction.

6. FRICTION IS SOMETIMES USEFUL Friction is useful for many of our daily activities. Friction between the feet and ground helps us to walk on the ground. It is possible to write with a pen or pencil on a paper due to friction

between the pen or pencil and the paper. It is possible to write on a blackboard due to the friction between the

chalk and black board. Friction between the tyres and the road helps automobiles to move

on roads. Friction between the bricks helps in the construction of buildings.

7. FRICTION IS SOMETIMES UNDESIRABLE Soles of shoes wear out due to friction. Tyres of bicycles and automobiles wear out due to friction. Steps of staircases and foot over bridges in railway stations wear out due to friction. Knives and razors lose their sharp edges due to friction.

8. INCREASING FRICTIONFriction can be increased by increasing the roughness of thesurfaces in contact.Eg :-1.The soles of shoes are grooved to have a better grip on the floor.2.The tyres of vehicles are treaded to increase the grip on the road.3.The break pads of vehicles are rough to stop moving vehicles when the

breaks are applied.4.Gymnasts apply some coarse substance on their hands for a bettergrip.

9. REDUCING FRICTIONFRICTION CAN BE REDUCED BY :- Using lubricants like powders or oils and grease. Using rollers or wheels. Using ball bearings. We sprinkle powder on a carrom board to reduce friction. Oil or grease is applied between moving parts of machines to

reduce friction. Rollers are used in luggage bags to reduce friction. Wheels are used in vehicles to reduce friction. Ball bearings are used in ceiling fans, bicycles and vehiclesto reduce friction.

10. FLUID FRICTIONFluid friction is the force of friction exerted by liquids andgases on objects moving through them.Fluid friction depends upon :-1.The speed of the object.2.Shape of the object.3.The nature of the fluid.

Eg:-Birds flying in air have streamlined body to reduce fluidfriction.Fishes living in water have streamlined body to reduce fluidfriction.Aeroplanes and spacecrafts have streamlined body toreduce fluid friction.

How to measure friction Measures of friction are based on the type of materials thatare in contact.Each material has what is known as a coefficient offriction. The coefficient is a measure of how easily oneobject moves in relationship to another.

When you have a high coefficient of friction, you have a lotof friction between the materials.Concrete on concrete has a very high coefficient offriction.A material such as Teflon (on most things) has a very lowcoefficient. Teflon is used on surfaces where we don't wantthings to stick; such as pots and pans.