full chapter explanation of NCERT of class 8 'FRICTION' i hope you understand it clearly and if you have any queries leave a comment i will try to reply it. there are some videos you can go through it which make your concept more clear ;). i have written everything in a very simple language to make you all understand clearly . there are some textbook exercise in the ppt try to solve it so that you can make your chapter more clear. and last and final there is a recap you can take it as your notes and make your concept more clear

1. FRICTION
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2. HAVE YOU EVER THOUGHT ??
Why any ball moving on a surface stops after travelling certain distance
without the act of external force?
Why vehicles slow down when brakes are applied ?
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3. Why it is difficult to walk on smooth and wet floor ?
Why we fall when we step on banana peel?
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4. It is an opposing force that opposes the motion of one body over
the surface of another body.
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5. • Frictional force comes to notice only when two surfaces
comes in contact with each other (contact force).
• It is offered by solid, liquids and gases.
• It is maximum in solids and minimum in gases.
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6. • The surfaces of solids that appear to be smoother are not actually
smooth they posses some irregularities that is ridges and grooves.
• When these type of surfaces come in contact with other surface their
ridges and grooves get interlocked and opposing force comes into
notice which opposes the motion. Force of friction
always act in
opposite direction
to motion of
applied force.
CAUSES OF FRICTION
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7. FACTORS AFFECTING FRICTION
1. NATURE OF SURFACES :
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8. Swati Mathur, Science teacher, MLZS Hayathnagar 8

9. Weight is a force
acting on a
matter due to
gravity.
10N= 1kg
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10. ACTIVITY
cloth
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11. 2. WEIGHT (NORMAL FORCE):
More is the weight of the body more is the friction.
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12. Swati Mathur, Science teacher, MLZS Hayathnagar 12

13. •Friction is the force that opposes motion
between any surfaces that are in contact.
•There are four types of friction: static,
sliding, rolling, and fluid friction.
•Static, sliding, and rolling friction occur
between solid surfaces.
•Fluid friction occurs in fluids, which are
liquids or gases.
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14. • Sliding friction is
slightly smaller
than the static
friction.
• We find it
somewhat easier
to move the box
already in motion
to get it started.
• Static friction > Sliding friction > Rolling friction
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15. INCREASING AND REDUCING FRICTION
INCREASING :
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16. Reducing:
In some situations friction
is undesirable and we
would want to minimize it.
When oil or grease is
applied between the
moving parts of a
machine, a thin layer
is formed there and
moving surfaces do
not directly rub each
other. Interlocking of
irregularities is
avoided to a great
extent and movement
becomes smooth.
The substances which
reduce friction are called
lubricants.
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17. Wheels reduce friction
• When one body rolls over
the surface of another
body, the resistance to its
motion is called rolling
friction.
• Rolling reduces friction.
• Rolling friction is smaller
than sliding friction.
• Sliding is reduced in most
machines by using ball
bearings.
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18. Swati Mathur, Science teacher, MLZS Hayathnagar 18

19. Friction: A Necessary Evil
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20. FLUID FRICTION
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21. What we have learnt :
• Force is an opposing force that opposes the motion of one body over the surface of another body.
• Frictional force comes to notice only when two surfaces comes in contact with each other (contact force).
• It is offered by solid, liquids and gases.
• The surfaces of solids that appear to be smoother are not actually smooth they posses some irregularities that
is ridges and grooves. When these type of surfaces come in contact with other surface their ridges and grooves
get interlocked and opposing force comes into notice which opposes the motion.
• Factors affecting friction:
✓ nature of surfaces….rough and smooth surfaces
✓ weight (normal force)….more is the weight of the object, more is the friction
• There are four types of friction: static, sliding, rolling, and fluid friction.
• Static, sliding, and rolling friction occur between solid surfaces.
• Fluid friction occurs in fluids, which are liquids or gases.
• Sliding friction is slightly smaller than the static friction.
• Rolling friction is smaller than sliding friction.
• Friction can be increased by making a surface rough.
• Friction is sometimes undesirable.
• Sliding is reduced in most machines by using ball bearings.
• Friction can be reduced by lubricants.
• Fluid friction can be minimized by giving suitable shapes to bodies, moving in fluids.
https://youtu.be/M8LlytVuABA
Friction
https://youtu.be/Fd9a24c1iy4
Friction (5min)
https://youtu.be/B6mi1-YoRT4
Frictional force
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