The document discusses friction and its various aspects in 3 paragraphs or less: Friction is a force that opposes the relative motion between two objects in contact. It causes moving objects to slow down and stop, like a rolling ball or pedaling bicycle. Friction depends on the nature and smoothness of the surfaces in contact and how hard they are pressed together. There are three main types of friction: static, sliding, and rolling, with rolling friction being the smallest. While friction can be useful to hold objects or enable motion, it also causes unwanted wear and tear over time.

1. B.J.P.S Samiti’s
M.V.HERWADKAR ENGLISH MEDIUM HIGH SCHOOL
CLASS 8th: FRICTION
Program:
Semester:
Course: NAME OF THE COURSE
Staff Name: VINAYAK PATIL 1

2. FRICTION
• Force of Friction : Force of friction is a force which
opposes the motion of an object over a surface.
• Example: A ball is rolling on ground gradually slows
down and comes to rest due to friction between the ball
and the ground.
• If we stop pedaling a bicycle it gradually slows down
and comes to a stop due to force of friction between the
wheel and the road.
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•If you apply the force along the left,
friction acts along the right.
•If you apply the force along the right, the
friction acts along the left direction.
•The force of friction always opposes the
applied force.

5. FACTORS AFFECTING FRICTION
•Friction depends upon two factors they are
 Nature of the surface in contact ( The
smoothness of the surfaces).
 How hard the surface press together.
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7. CAUSES OF FRICTION
• Friction is caused by the
irregularities on the two surfaces
in contact.
• Smooth surfaces, have a large
number of minute irregularities
on them
• On rough surfaces, there are a
larger number of irregularities.
So the force of friction is greater
if a rough surface is involved.
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8. TYPES OF FRICTION
•There are three main types of friction
Static friction: static friction is the friction
exerted on object at rest.
Sliding friction: sliding friction is the
friction exerted when an object slides over
a surface .
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9. Rolling friction: rolling friction is the friction exerted when
an object rolls over a surface .
Sliding friction is slightly smaller than the static friction.
Rolling friction is smaller than the sliding friction and
static friction.
Rolling reduces friction. It is always easier to roll than to
slide a body over another. That is the reason it is convenient
to pull luggage fitted with rollers.
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11. FRICTION IS SOMETIMES USEFUL
• It is possible to hold tumbler due to friction between
the hand and the tumbler.
• It is possible to write with a pen or pencil on a paper
due to friction between the pen and the paper.
• It is possible to write on a blackboard due to friction
between chalk and blackboard.
• Friction between the tyres and the roads helps
automobiles to move on roads.
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13. FRICTION IS SOMETIMES
UNDESIRABLE
•Friction is an evil, too. It wears out the
materials whether they are screws, ball
bearings or soles of shoes You must
have seen worn-out steps of foot over-
bridges at railway stations.
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15. INCREASING FRICTION
• Friction can be increased by increasing the roughness of the
surfaces in contact.
• Example: the sole of your shoe is grooved. It is done to provide the
shoes better grip on the floor.
• The treaded tyres of cars, trucks and bulldozers provide better grip
with the ground.
• The brake pads of a vehicles are rough to stop moving vehicles when
the brakes are applied.
• Gymnasts apply some coarse substance on their hands to increase
friction for better grip.
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17. REDUCING FRICTION
• Friction can be reduced by
 Using lubricants like powders or oils and grease
 Using rollers or wheels.
 Using ball bearings.
• Example: sprinkle fine powder on the carrom board to reduce friction.
• Oil, grease or graphite is applied between the moving part of a machine to
reduce friction.
• The substances which reduce friction are called lubricants.
• In some machines, it may not be advisable to use oil as lubricant.
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19. FLUID FRICTION
• Fluid friction is the force of friction exerted by liquids and gases on
objects moving through them.
• Fluid friction depends on:
 The speed of the object.
 Shape of the object.
 The nature of the fluid.
• The frictional force exerted by fluids is also called drag.
• Birds and fishes have to move about in fluids all the time. Their
bodies must have evolved to shapes which would make them lose less
energy in overcoming friction
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21. HOMEWORK
1) Define friction.
2) Name the three types of friction.
3) Write the factors which are affecting the
friction?
4) Define rolling friction.
5) How friction can be reduced
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