1.71 Energy

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1.71 Energy

Energy

Energy

can be transformed from one type to another and stored, it cannot be

created or destroyed. This is known as the principle of conservation

of energy.

Energy is Measured in joules.

Types of Stored Energy

G.P.E

- Gravitational Potential energy

Kinetic

– The energy an object has due to its movement – e.g. a person

running gains kinetic energy

Chemical

– Stored energy, released in chemical reactions – e.g. a battery

Strain

– Energy stored when an object changes shape – e.g. a stretched

rubber band

Nuclear

– Stored energy released in nuclear reactions e.g. energy

stored in the sun

Internal

Energy – The total kinetic and potential energies of the

particles in an object

Types of Transfer Energy ( Energy

on the move from place to place)

Electric

– Energy carried by an electric current

Sound

– Energy carried by a sound wave

Thermal

(heat) energy – The energy released when the temp of a hot

object decreases due to a decrease in internal energy

Light

– Energy given off – e.g. by very hot objects

Energy is transfered during events and processes

Heat energy can be transfered from a hot object to a cooler one

Kinetic energy can be transferred from one car to another in a collision

Electrical energy can be transferred in a circuit

Principle of conservation of energy

Energy cannot be created or destroyed. It is transformed from one form to another

( view diagram on page 39 )

Kinetic energy

Change in Gravitational portential energy

Change in GPE = mgΔh

Acceleration of free fall = 10m/s²

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1.72 Energy Resources

Nuclear Fusion

The process of nuclear fusion is carried out in the Sun. Hydrogen nuclei collide at great speed in the sun and fuse together to form helium nuclei. This releases energy in the form of heat and light. The sun is therefore the source of all energy resources, except geothermal, nuclear and tidal

Coal,oil and gas fired power stations

Burn the chemical fuel to release chemical energy, which is transformed to heat energy.

The heat is then used to heat a liquid such as water and increase its internal energy which is then turned into steam.

The pressure from the steam is used to spin a turbine, transferring its kinetic energy to them.

The kinetic energy is transformed to electrical energy in the generators

Advantages

Coal will not run out for many years

Reliable source of energy

Disadvantages

Produces gaseous polution - Carbon dioxide ( contributes to global warming ) & Sulfur dioxide ( causes acid rain )

Non-renewable

Geothermal power stations

Possible to use the natural heat of the earth to generate electricity.

Cold water is first pumped underground gaining heat energy from hot rocks underground

The heat energy is then converted to kinetic energy in turbines

The turbines turn the generator to produce electrical energy

Advantages

Renewable

Doesn'tproduce carbon dioxide or sulphur dioxide

Reliable source of energy

Disadvantages

Few areas where it is available

Hydroelectric power stations

The G.P.E of falling water is transformed to kinetic energy as it passes through turbines

The turbines turn the generator, producing electrical energy

Advantages

Renewable

No carbon dioxide or sulphur dioxide

Energy can be stored as GPE of water

Disadvantages

Land is flooded to build reservoirs - destroys farmland, habitats and peoples homes

Solar Cells

The light energy from the sun is transformed to electrical energy in the solar cell

Advantages

Can be used remotely

No carbon dioxide or sulphur dioxide

Renewable

Low maintenance

Disadvantages

Solar cells are inefficient and expensive - payback time is long

Unreliable - can't be used at night and input during cloudy weather is low

Solar power station

Heat energy from the sun is concentrated by a series of mirrors , focusing energy into one place

This heat energy converts water to steam

The steam turns the turbines giving them kinetic energy.

The kinetic energy is transformed to electrical energy in the generators

Advantages

Renewable

No carbon dioxide or sulfur dioxide

Disadvantages

The array of mirrors occupy a large area

Unreliable

Wave power

Turbines bob on the surface of the sea,transforming G.P.E into kinetic energy

Kinetic energy is then transformed into electrical energy in the generators

Advantages

Renewable

No carbon dioxode or sulfur dioxide

Disadvantages

Unreliable - cannot be used in stormy conditions & output is low on a calm day

DIfficult maintenance

Interferes with shipping

Tidal Power

As the tide comes in water builds up behind a dam gaining G.P.E

When the water is released G.P.E is transformed to kinetic energy

The kinetic energy is transformed into electrical energy in the generator

Advantages

Renewable

No carbon dioxide or sulfur dioxide

Reliable - ( two tides a per day )

Disadvantages

Expensive to build

Few places with suitable conditions

Nuclear power

The nuclear energy stored in uranium-235 is released when uranium nuclei split in a process called nuclear fission ( REMEMBER this is different to nuclear fusion )

The nuclear energy is transformed to heat energy

The heat energy is used to turn water to steam

The steam turns the turbines, transforming the energy into kinetic energy

This kinetic energy is transformed into electrical energy in the generator

Advantages

Plentiful supply of uranium 235

Concerntrated energy resource - a large amount of energy for small amount of fuel

No carbon dioxide or sulfur dioxide

Reliable source of energy

Disadvantages

Non-renewable

Disposal of nucleur waste is problematic - it has a long half-life and the emitted radiatio nis dangerous

Wind power

The kinetic energy of moving air is transferred to the blades

The blades spin, turning the generators

In the generator kinetic energy is transformed into electrical energy

Advantages

Renewable

No carbon dioxide or sulfur dioxide

The area around wind turbines can be used as farmland

Disadvantages

Unreliable - cannot be used in very winds & output is low on calm days

Noisy & unsightly

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1.73 Work

To lift an object, you need a store of energy. You give the object more g.p.e. The force is your means of transfering energy from you to the object. The name given to this type of energy transfer by a force is doing work. The more work a force does, the more energy it transfers,so: Work done = energy transferred

The amount of energy transferred by a force depends on two things:

The size of the force - the greater the force, the more work it does

The distance moved in the direction of the force - the further it moves, the more work it does

So a big force moving through a big distance does more work than a small force moving through a small distance

Calculating work done

We know that the amount of work done = change in energy ( or ΔE ) so :

work done (joules) = force (n) x distance moved by the force in the direction of the force (m)

or W = F x D = ΔE

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1.74 Power

In physics the word power has a special meaning. It means the rate you do work. The more work you do, and the shorter the time in which you do it, the greater your power. Power is therefore the rate at which energy is transferred or the rate at which work is done. It is measured in watts, that is joules per second.

In summary, the power in watts is the work done per second or energy transformed per second

Power (w) = energy transferred (j) ÷ Time (s)

or

P = ΔE ÷ T