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NAVODAYA VIDAYALAYA SAMITI , NOIDA

E-CONTENT PREPARATION FOR CLASS VIII

SUBJECT- SCIENCE

CHAPTER-12 ‘FRICTION’

PREPARED BY – MRS. ANUPMA

[TGT SCIENCE, J.N.V BEGUSARAI, BIHAR]

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LEARNING OUTCOMES -

EXPLAIN THE TERMS FRICTION AND DRAG.
LIST ADVANTAGES AND DISDVANTAGES OF FRICTION
DIFFERENTIATE BETWEEN STATIC FRICTION AND SLIDING FRICTION.
TABULATE METHODS OF INCREASING AND REDUCING FRICTION.

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CONTENT TO BE COVERED

1.INTRODUCTION TO FRITION
2.CAUSE OF FRICTION
3.TYPES OF FRICTION
4.DIFFERENCE BETWEEN TYPES OF FRICTION
5.NECESSITY OF FRICTON
6. DISADVANTAGES OF FRICTION
7.METHODS TO REDUCE FRICTON
8.RECAP
9.BIBLIOGRAPHY

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INTRODUCTION

WHAT IS FRICTION?

Friction is the force that opposes motion between surfaces that are in contact.

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It comes in notice when only when two surfaces are in contact with each other. It is called contact force . It is offered by Solid , Liquids, and gases but It is maximum in case of solids and least in case of gases.

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CAUSES OF FRICTION

The surface of solids etc. That appears to be smoother are not actually smooth they posses some irregularities that is ridged and grooves.
When these type of surfaces come in contact with other surface their

ridges and grooves get

interlocked .

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FACTORS AFFECTING FRICTION

1. NATURE OF THE SURFACE – MORE IS THE ROUGHNESS MORE IS THE FRICTION .

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2.WEIGHT{NORMAL FORCE} – MORE IS THE WEIGHT OF BODY, MORE IS THE FRICTION.

3.SURFACE IN CONTACT- MORE IS THE SURFACE OF CONTACT ,MORE IS THE FRICTION.

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TYPES OF FRICTION

STATIC FRICTION

SLIDING FRICTION

ROLLING FRICTION

FLUID FRICTION (DRAG)

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TYPES OF FRICTION:

1.STATIC FRICTION- It is friction between two or more solid objects that are not moving relative to each other. For example- pushing anything etc.

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2.SLIDING FRICTION- It is the resistance created by any two objects when sliding against each other. This friction is also known as kinetic friction .

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3. ROLLING FRICTION-Rolling friction is the frictional force that occurs when one object rolls on another, like a car's wheels on the ground.

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4. FLUID FRICTION- (drag) It is friction that occurs when objects move across or through a fluid. For ex- Swimming – swimmer’s body and surface of water

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FACTORS AFFECTING DRAG

1. SPEED OF THE OBJECT WITH RESPECT TO FLUID- MORE IS THE SPEED OF THE OBJECT MORE IS THE FRICTION
2.NATURE OF FLUID- DENSER THE FLUID, GREATER THE FRICTION
3.SHAPE OF THE OBJECT-MORE IS THE SURFACE AREA OF THE OBJECT , MORE IS THE FRICTION

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ORDER OF STRENGTH OF DIFFERENT TYPES OF FRICTION

Static Friction > Sliding Friction > Rolling Friction

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APPLICATION/ NECESSEITY OF FRICTION

Friction finds application when matchsticks are ignited.
Motion of pistons in a cylinder is an application of friction.
It is possible to write on books and board as there is friction between pen and the board.
Friction is also responsible for the wear and tear on bike gears and other mechanical parts.

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It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it becomes difficult to walk due to low friction of ice.
We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
A horse can not pull a cart unless friction furnishes him a secure Foothold.

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DAILY LIFE EXAMPLES OF FRICTION

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DISADVANTAGES OF FRICTION

The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
Due to friction we have to exert more power in machines.
It opposes the motion.
Due to friction, noise is also produced in machines.
Due to friction, engines of automobiles consume more fuel which is a money loss.
It causes wear and tear of sole of shoes.

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METHODS OF REDUCING FRICTION

1.USE OF LUBRICANTS:

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

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2.USE OF BALL BEARING:

In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.

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3.DESIGN MODIFICATION:

Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.

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4.STREAMLINED BODY-

A streamlined body is a shape such that it helps to reduce the friction between a fluid and an object moving through that fluid.

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RECAPTULATION

FRICTION IS A TYPE OF FORCE WHICH RESIST MOTION.
INTERLOCKING BETWEEN SURFACE CAUSES FRICTION
TYPES OF FRICTION- 1. STATIC, 2.SLIDING , 3.ROLLING 4.FLUID FRICTION
FRICTION IS A NECESSARY EVIL.
METHODS OF REDUCING FRICTION-1. USE OF LUBRICANTS, 2. USE ODF BALL BEARING, 3. DESIGN MODIFICATION, 4.STREAMLINED BODY