Question

Friction Chapter full notes Class 8

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Answer 1

$\huge{\tt{\red{}\green{A}\purple{N}\pink{S}\blue{W}\orange{E}\red{R}}}$

Friction :

• Friction is a force between two surfaces that are sliding, or trying to slide, across each other.
• For example, when you try to push a book along the floor, friction makes this difficult.
• Friction always works in the direction opposite to the direction in which the object is moving, or trying to move.
• There are four types of friction: static, sliding, rolling, and fluid friction.
• Static, sliding, and rolling friction occur between solid surfaces.
• Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest.
• Fluid friction occurs in fluids, which are liquids or gases.

Everyday Examples of Friction :

• Rubbing both hands together to create heat.
• A sled sliding across snow or ice.
• Skis sliding against snow.
• A person sliding down a slide is an example of sliding friction.
• A coaster sliding against a table.
• A washing machine pushed along a floor.
• An iron being pushed across material.

Answer 2

Friction is a force that opposes the relative motion between two surfaces of objects in contact. The force of friction always acts in a direction opposite to that of the applied force.

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$\red{ \underline{ \large \bold{Cause \: of \: friction:- }}}$

» Friction is caused by the interlocking of irregularities in the surfaces of two objects which are in contact with each other. In order to move one object over the other, we have to apply force to overcome interlocking.

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$\blue{ \underline{ \large \bold{Factors \: affecting \: friction:- }}}$

» The nature of the two surfaces (roughness of the two surfaces)

» The force with which two surfaces are pressed together

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$\pink{ \underline{ \large \bold{Spring \: balance :- }}}$

» A force can be measured using a spring balance.

» The unit of force is Newton (N)

» The pointer of the spring balance will be at zero, when nothing is hung from the hook of the spring balance.

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$\green{ \underline{ \large \bold{Calculating \: frictional \:force \: using \: a \: spring \: balance:- }}}$

» To determine the coefficient of friction between two surfaces, pull an object placed on a surface using a spring balance that is used to measure weight/ force in the unit Newton(N).

» Pull a spring balance connected to the object and slowly increase the force until the object begins to slide on the surface.

» Make sure the spring balance is parallel to the surface. The reading on the spring balance scale when the load/ object begins to slide is a measure for the static friction, while the reading when the block continues to slide is a measure of sliding friction.

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$\purple{ \underline{ \large \bold{Friction \: is \: of \: three \: types :- }}}$

» Static friction: The Frictional force that comes into play until an object starts moving is called static Friction. When a body is at rest, the force of friction is called the static friction

» Sliding friction: The frictional force present when one object slides over the surface of another object is known as sliding friction.

»Rolling friction: When an object rolls over the surface of another object, then the frictional force that comes into picture is called rolling friction.

NOTE: Static friction > Sliding friction > Rolling friction

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$\red{ \underline{ \large \bold{Advantages \: of \: friction :- }}}$

» Frictional force is necessary for various purposes in our daily lives such as:

» It is the friction between the sole of our shoes & ground that enable us to walk without slipping.

» It is the friction between brake pad and rim that prevents the wheel from moving ahead. Due to this, the running bicycle slows down & finally stops.

» Friction enables us to write with a pen on a surface or a paper. It is due to the friction between tip of the pencil & paper that rubs off black graphite particles from the tip of the pencil which stick to the paper & leave black marks on paper.

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$\blue{ \underline{ \large \bold{Disadvantages \: of \: friction :- }}}$

» Friction wears away the soles of our shoes.

» Due to friction between the surface of tyres & the surface of road, the tyres wear out gradually.

» Friction wears out the brake pads of vehicles gradually. As a result brake pads of cycles have to be replaced quite often.

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$\pink{ \underline{ \large \bold{How \: can \: we \: reduce \: or \: incerease \: friction :- }}}$

Methods of increasing friction:

» The sole of the shoes is grooved so that the Friction between our feet and ground increases and we can walk safely

» The tyres are treaded so that they can have a better grip over the ground and allow the smooth movement of the vehicles.

» Brake pads are used in bikes to stop them suddenly from moving by increasing the amount of Friction

»Kabaddi players rub their hands with soil which helps in increasing the Friction between the hands and allows them to have an easy grip of the opponent.

Methods of increasing friction:

» The powder is sprinkled over the carrom board to decrease the Friction between the board’s surface and the striker.

» By making the surface smooth by polishing.

» By applying lubricants (like oil or grease).

» Applying oil or grease helps in avoiding interlocking between the two rubbing surfaces to a large extent. As a result, friction is reduced.

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$\green{ \underline{ \large \bold{Fluid \: friction :- }}}$

Friction exerted by fluids i.e. gases or liquid is termed as fluid friction or drag.

The magnitude of drag (fluid friction) depends on

» Speed of the object with respect to the fluid.

» Shape of the object

» Nature of the fluid.