The document discusses friction, including the factors that affect friction, the causes of friction, the different types of friction, and how friction can be both useful and undesirable. Friction is the force that opposes the motion of objects in contact with each other. It depends on the nature and roughness of the surfaces, as well as how hard the surfaces are pressed together. There are different types of friction including static, sliding, and rolling friction. Friction can be increased by making surfaces rougher and decreased by using lubricants.

1. CHAPTER -
12
FRICTION

3. 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.

5. FACTORS AFFECTING
FRICTION
Friction depends upon two factors. They are :-
i)Nature of the surfaces in contact. ( The smoothness of the
surfaces).
i) How hard the surfaces press together.
Friction is less on a smooth surface.

6. Friction is more on a rough
surface.

7. Is friction more if the surfaces are pressed harder?

8. Friction is more if the surfaces are
pressed harder
Friction is less if the surfaces are
not pressed harder

9. CAUSE OF FRICTION
Friction 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.

10. Phet simulation
Phet simulation
https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

11. TYPES OF FRICTION
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. .
a)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
surface.
Sliding friction is slightly less than static friction.
Rolling friction is less than sliding friction and static friction.

14. Sliding friction

15. 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 blackboard.

16. Friction between the tyres and the road
helps automobiles to move on roads.
Rubbing both hands together to create heat.

18. Give more examples of useful
applications of friction in our daily life

19. 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.

21. INCREASING FRICTION
Friction can be increased by increasing the roughness of the
surfaces in contact.
Eg :-
● The soles of shoes are grooved to have a better grip on the
floor. The tyres of vehicles are treaded to increase the
grip on the road.
● The break pads of vehicles are rough to stop moving vehicles
when the breaks are applied.
● Gymnasts apply some coarse substance on their hands for a
better grip.

23. REDUCING FRICTION
FRICTION 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 vehicles
to reduce friction.

25. Summarize what
you’ve just learned:

26. FLUID FRICTION
Fluid friction is the force of friction exerted
by liquids and gases 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.