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Thursday, 13 September 2012

Energy, Conservation of Energy and Machines to save Human Energy

ENERGY:

Picture of Energy Page in my (Manash Kundu) Physics-World Software

WORK AND ENERGY:

A man carrying sacks of potatoes up some stairs is doing work.The amount of work that he does depends not only on the weight of the sacks but also on the height to which they are carried.One man carrying a sack to height of 12 meters is doing twice as much work as man who carries a similar sack up 6 meters.Also man who carries a 20 kg sack up 6 meters has done twice as much work as a man who only carries  a 10 kg sack up to the same height. So work involves both force and distance the work done equals the force used multiplied by the distance for which the force is used. According to this idea work is only done when a force moves.
EQUATION:-

W = F * s  (where W = work, F = force, s = distance).

POTENTIAL AND KINETIC ENERGY:

Strictly speaking if you hold the heavy book above your head no work is done on the book because it has not moved. However some work is done by the contraction and expansion of your muscles. If you lift weight on to a self you have to do work and put it there. This work is not wasted .The weight has more energy than it had when it was on the floor.This stored energy is called potential energy.If the weight falls from the shelf it losses this potential energy .It falls faster and faster gains a new kind of energy called kinetic energy ,kinetic energy is a kind of energy due to the motion of a body.

Paddle a Cycle produce movement of man who Paddle and produce kinetic energy for movement 

If the weight drops on to some sand or soft soil it makes a hollow where it falls .The kinetic energy has been used up in doing work to move the soil it makes a hollow where it falls.The kinetic energy has been used up in doing work to move the soil.The energy of a body is its ability to do work.Energy is never lost but it can be changed or converted from one from to another.

OTHER FORMS OF ENERGY:
What happens if a falling weight hits a hard floor? Where does it energy go? some of the kinetic energy is used in making a noise.Some of it may be used to knock the weight out of shape.The remainder is turned into another form of energy which it call heat. The weight is slightly hotter.You can show how kinetic energy is turned into heat by hitting a small piece of metal with a  hammer a number of times.The metal quickly become quite hot.

Of course hitting things is not the best way to make  them hot .Burning things is much  better  way of producing heat when coal burns , heat is given out.We say that the coal is source of energy the energy is stored in the coal and when the coal burns it forms a new chemicals. These have less energy than the coal .The rest of the energy is converted into heat.

The heat from coal can be used to make steam which drives steam engine. In turn the steam engine can be used to do work.

You also use up a fuel when you do work such as lifting a weight or pushing something. The fuel is the food you eat.


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                                                                              3D animation showing lifting a weight and pushing something


You also use up a fuel when you do work such as lifting a weight or pushing something. The fuel is the food you eat. Chemical changes in the food provide the energy. The energy stored in things like food, coal , petrol,and gas is called chemical energy.

Coals and fuels are burn to produce electricity in Electric Power Station

There other forms of energy. For example when things burn they give out light as well as heat.Part of the energy is converted into light energy.In an electric fire heat and some light are produced from electrical energy.   

FORCE:
If you lift  a box you exert a force on it to overcome the force of gravity .You also move this force through a certain distance in other words you do work on the box .If you push the box along the ground you also exert a force on it to overcome the friction between the ground and the box.

James Watt(1736-1819)

James Watt(1736-1819): was a Scottish engineer and inventor . He designed an efficient steam engine with many improvements shortly after such machines had been invented.

James Watt Steam Engine

When the arrow is released the potential energy of the bent bow is changed into the kinetic energy of the moving arrow.


Picture of Conservation of Energy Page in my (Manash Kundu) Physics-World Software

CONSERVATION OF ENERGY :
Imagine a car is moving along the road and the driver has to stop quickly. She applies the brakes. -That is, applies a force to the wheels to stop them going round. If the car is moving at 70 mph it takes more force to stop it than if it in moves at only 30 mph.Now think of a lorry moving at 70 mph. It takes more force to stop a lorry than to stop a car moving at the same speed .This is because the lorry is heavier than the car .We say that the car and the lorry have momentum.

If the car is moving at 70 mph it takes more force to stop it than if it in moves at only 30 mph.Now think of a big Double Decker Bus moving at 70 mph. It takes more force to stop a lorry than to stop a car moving at the same speed


Momentum depends not only on the speed of a thing but also on its mass. A lorry traveling at 70 mph has more momentum than a car traveling at 70 mph.A car traveling at 70 mph has more momentum than if it travels at 30 mph.The momentum of anything is its mass multiplied by its velocity.

EQUATION IS:-

M = m * v (where M = momentum, m = mass, v = velocity)

LAW OF CONSERVATION OF MOMENTUM:

Scientists have found out that when things collide their total momentum is unchanged .This is called the law of conservation of momentum. Suppose you are sliding on ice and you catch hold of someone as you are going past them .You will both move together but your combined speed will be less than your original speed .This is because your original momentum is being shared between two people.

Energy Conservation


LAW OF CONSERVATION OF ENERGY:
The law of conservation of momentum is one of the important principles in physics.There is a similar law concerning energy. It says that energy is neither created nor destroyed but it simply changed from one form to another .It is called the law of conservation of energy.



EQUATION:-

Em = Ek + Es (whereas Em = mechanical energy, Ek = kinetic energy, Es = static energy)

Static energy of any material or body can be turned into kinetic energy and vise versa  but total mechanical energy of any material remain same. When a body fall of mass m, from height h, at initial stage or at rest,its whole mechanical energy is its static energy ,therefore Em = Es = mgh (where m = mass, g = gravity, h = height) during the falling its height and static energy gradually decrease but it kinetic energy Ek = mv (where m = mass and v = velocity) is increasing. When a body fully fall its static energy turned totally into kinetic energy (Em = Ek = mv). So here total mechanical energy is remained
same.

Coal is burned in a power station and gives heat .This is used to produce steam for driving a turbine .The turbine turns a generator and gives electricity


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                                                                                            3D animation showing how electricity produced in power station by burning coal and steam energy drive turbine which turns generator.


Coal is burned in a power station and gives heat .This is used to produce steam for driving a turbine .The turbine turns a generator and gives electricity.In an electric fire the electrical energy is converted into heat.In this way the chemical energy in the coal has been used to provide heat energy in the electric fire. However all the chemical energy in the coal does not reach electric machines.some of the energy is lost along the way .For example in the turbine and generator ,friction in the moving parts causes heat. Some of the electrical energy is used in warming the wires and cables carrying the electric current .This energy is not used for any useful purpose .However the important thing is that no energy is really lost overall .It is just converted to other forms.

In prehistoric times heat and light energy from the sun was used by growing trees and plants .These eventually changed to fuels such as coal,oil, and natural gas

In prehistoric times heat and light energy from the sun was used by growing trees and plants .These eventually changed to fuels such as coal,oil, and natural gas .When we burn these fuels. We release the energy that reached the earth from the sun many years ago .This is stored in the fuel as chemical energy.

Over the last fifty years people have discovered and developed a new source of energy called nuclear energy.  


 NEWTON`S CRADLE:


Imaginative 3D picture of Newton`s Cradle created by me (Manash Kundu)



When the ball at one end strikes the line of stationary balls, its energy is transmitted along the line and ball at the other end flies up . 

Imaginative 3D picture of Newton`s Cradle created by me (Manash Kundu)



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                                                                                      3D animation showing imaginative Newton`s Cradle

With highly polished steel balls on fine supporting threads, very little energy is lost and the movement continues for a long time without anyone touching the cradle.



powerful laser beam is sufficient to bore a hole through a thick Aluminium plate.

The energy in the powerful laser beam is sufficient to bore a hole through a thick Aluminium plate.

Picture of Machines Page in my (Manash Kundu) Physics-World Software

MACHINES:

A machine in any device that overcomes a force at one place by enabling a force to be applied some where else.A knife is a very simple example of a machine.

Claw Hammer pushing nail into the table


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                                                                                                   3D Animation showing utility of Hammer and Screw Driver.

when you push on the knife , you produce a cutting force in the blade .Another example is a claw hammer ,which is use to pull out nails .Both of these  machines are levers. Through machines we can do work  more efficiently.

A pulley is a wheel with a groove along its edge, for holding a rope or cable. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load

Another type of machine is a pulley.A simple pulley enables a heavy to be lifted up by pulling downwards .It is much easier to lift something heavy ,Such as the engine from a car ,by pulling downwards .We can use the natural downward pull of gravity on the weight of our bodies.

If a large load can be raised using a small effort, this is an advantage .The mechanical advantage, as it is called, is equal to the load divided by the effort .The greater the load than can be raised for a govern effort, the greater is the mechanical advantage.

Wooden Pulley with rope used to pull up water filled large heavy bucket of water from the deep village well

However we cannot get something for nothing. Pulley allow us to lift a large weight by using small force .But we have to move the rope much further down-ward than the weight moves upwards. So the effort we apply moves much further than the load.In fact the work we do raising a weight with a pulley is not less than the work we would do lifting the weight directly. Work in physics, is defined as the force applied to anything, multiplied by the distance through which the things moves. To raise a car engine weighing 100 kilograms a distance of 2 meters might require an effort of 50 kg applied to a pulley rope. This effort would have to move 4 meters.We say that the work done by the effort is the same as the work done on the load.

Wooden Pulley with rope used to pull up water filled large heavy bucket of water from the deep village well


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                                                                                         3D animation showing how rope pulley pull out heavy water filled bucket from the deep well easily in village.

In practice the figures would not work out quite like this because no machine is 100% efficient. That is not all the work put as an effort can be used to raise the load. Some work is lost in friction.The efficiency of a machine is the work actually applied to the load divided by the work put in as effort .It is usually multiplied by 100 so that it can be expressed as percentage.The efficiency is never greater than 100 % and in practice is always much less.

SCREWS AND GEARS:

Screw Driver used to fixed the screw tightly into the wooden furnitures

Another machine in which the effort moves a larger distance than the load is the screw.Again. Large forces are produced by smaller ones .For every turn of the screwdriver the screw moves only a small distance into the wood. Overcoming very large friction forces as it does so . Imagine how difficult it would bet to insert a screw into wood without a screwdriver.

Screw Driver

The same principle is used in the car jack. In this device a large turn on the handle lifts the  car a very small distance .

Gears are also machines and they can operate in two ways .They can make large forces from small ones and they can make small forces from large ones.

Claw hammer show how loads are overcome using levers. Hammer is a simple machine

Gears in a car carry forces from the engine to the wheels

Gears in a car carry forces from the engine to the wheels . they also change the size of the forces depending on the load.When the car is starting or climbing a hill the engine has to be turn quickly although the wheels are only turning slowly.

















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