class 8 friction - Morescorecbse

Define Friction??

It is also called as Force of Friction
Force acting along the two surfaces in contact which opposes the motion of one object over the other is called Force of Friction.

What are the Causes of Friction??

Friction always act in the direction opposite to the direction of motion.
Friction depends upon the nature of the surface in contact. It also depends on the weight of the body.
Friction is greater than rough surface and smaller than smooth surface.
Friction is caused by interlocking of irregularities between the two surfaces
Friction is independent of area of contact.
Friction is also caused due to the Force of adhesion.

Write a short note on Spring Balance??

It is a device used to measure the force acting on a object.
It consists of a spring enclosed in a metal case.

Working Principle:

Spring stretchers when the force is applied.
The extent to which the spring extends it indicates the measure of applied force.
Stretching of the spring is indicated by the pointer and corresponding reading gives the magnitude of force.

List the various types of Friction??

There are Three types of friction

Static friction
Limiting friction
Kinetic friction

Static friction: The opposing force that comes when one object tends to move over the surface of another but the actual motion is not started.

Limiting friction: It is the maximum opposing force that comes when one object is at the verge of moving over the surface of another object.

Kinetic friction: It is the opposing force that comes when one object is actually moving over the surface of another object.

There are two types of Kinetic Friction: Sliding Friction and Rolling Friction.

Sliding Friction:

The opposing force that comes when one object is sliding over the surface of another object.
Ex: When a log of wood is moved on a flat surface, its slides

Rolling Friction:

The opposing force that comes when one object is rolling over the surface of another object.
Ex: When a wheel rolls over the flat surface.

How the Sliding friction is replaced by Rolling friction give example and explain??

Whenever possible sliding friction is replaced by rolling friction. It is achieved by wheels, ball bearings, rolling bearings, etc.
Ex: roller skates used by the children.
Roller skates have tiny wheels
These wheels have very small rolling friction and helps in the fast motion of the skater.
The same principle is applied in the suitcases and bags that have tiny wheels, so that they are convenient to pull.

What are the Factors affecting the Friction??

The force of the friction depends on the

Nature of the surface in contact with each other – Rough surface have more friction, Smooth surface have less friction.
Weight of the object – More Weight, More Friction. Less weight, Less friction.

Friction due to liquids:

Liquids and gases exert of friction on a solid surface or the object moving over them. This is called a Fluid Friction.
Liquids and gases exert lesser friction compared to the solid surface.
Frictional force exerted by the fluids is called as “drag”
When a person swims in water, the water opposes his motion. This is because, water exerts are force of friction on the swimmer in the opposite direction of his motion.

Define Streamlined shape??

Special shape of a body or an object around the fluid ( liquid or air) can flow offering minimum friction called Streamlined shape.
Ex: Fish bodies are streamlined, so that they experience least amount of friction in water. The bodies of the ships are also made streamlined up for the same purpose.

Friction due to air:

Air exerts force of friction on all the objects that move through it and opposes their motion.
But friction of the air is so small that we are not able to experience it.
The bodies of the birds are streamlined so that are the experience least amount of the friction in air.
The bodies of the aeroplane and bullet trains are streamlined so that they experience less friction while moving through the air.

List out some advantages of the Friction??

Help us to walk- The Friction between our feet and the ground help us to walk without slipping.
Movement of vehicles – The Friction between the tyres of various vehicles and the ground helps them to move without slipping. In Tyres friction is increased by making the grooves in them.
Spike shoes – The spikes in the shoes are provided for the athletics and players to increase the friction and have better grip on the ground.
Writing work – Friction between the tip of the Pen and the Paper help us to write.
Brakes – When we apply the brakes in our vehicle its stops due to the force of friction between the brake lining and the drum of the wheel.
Lightning of the Matchstick: When matchstick is striked against the rough surface of the Matchbox it catches fire. The force of friction raises the temperature of the matchstick head to such an extent that chemicals in it catch fire to produce the 🔥 Flame

What are the ways of Increasing the Friction??

By Making the Surface Rough

Friction can be increased by increase in the roughness of the surface in contact.
Ex: The surface of the head of the matchstick and the sides of the Matchbox is made rough to produce more heat and catches fire easily.

By making Grooves

The tyres of the vehicles are increased by making the grooves in them. Due to greater friction, tyres get better grip on the road and prevents kidding of the vehicles.

List out the disadvantages of the friction??

Damage to machine:

When moving, parts of the vehicles are rubbed together it produces lot of heat between them and can damage the machine gradually.

Wear and Tear

Friction causes wear and tear of the parts of the machines in contact, so their lifetime is reduced. Ex: Soles of shoes and tyres of vehicles.

Loss of energy

Friction always opposes the relative motion between any two objects in contact. So extra energy is spent in overcoming the friction.

Reduces the efficiency of the machine

Some of the force applied to run a machine is always wasted in overcoming the friction between its moving parts. This reduces the efficiency of the machines.

List the few ways of reducing friction??

Note: friction can only be reduced but can’t be zero

By Lubricating:

The substances that reduce the friction are called as Lubricants. Ex: oil or grease.
Lubricants is applied between the moving parts of the vehicle, a thin layer is formed on the moving surfaces do not directly rub each other.
It fills up the irregularities and make them smoother.
Talcum powder is a dry lubricant used in the carrom boards. Graphite powder is used in the machines to reduce the friction.

By Polishing:

Friction is greatly reduced by polishing. Polishing covers the irregularities of the surface and makes them smoother, so friction is reduced.
By using ball bearings
Ball bearings is a hollow circular device that have small metal balls that are fitted around the moving parts of a machine.
Ball bearing reduces the friction by converting the sliding friction into a rolling friction.
Ball bearings are used in the free wheels of bicycle, axle of the cars, shaft of the motors.

By using Rollers and Wheels:

Many heavy objects like suitcases are provided with the small wheels called as rollers, to reduce the friction so that they can be carried easily by pulling.

By Streamlining

The bodies of the car and aeroplane, boats and ships are streamlined to reduce the friction in air and water.

Note:

Wheels of the train and tracks are made up of Steel. This reduces the rolling friction and the train runs fast.
There is a heat shield at the nose of the space ships. This is done because, when the spaceship enter the atmosphere they do not catch fire due to the friction of air.

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