Energy

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Energy Stores and Systems

When energy is transferred to an object, energy is stored in one of the object's energy stores

Thermal Energy

Kinetic Energy

Gravitational Potential Energy

Elastic Potential Energy

Chemical Energy

Magnetic Energy

Electrostatic Energy

Nuclear Energy

Energy is transferred mechanically, electrically, by heating or radiation

System - a single object or group of objects

When a system changes, energy is transferred

Can be transferred into or away from system, between objects or between different types of energy

Closed systems - neither matter nor energy can enter or leave - net change in total energy of a closed system is always zero

For example, in a kettle energy is transferred to the water by heating into the water's thermal energy store

Energy is transferred electrically to the thermal energy store of the kettle's heating element - transfers energy by heating to the water's thermal energy store

Work done is just another way of saying energy transferred

Work can be done when current flows or by a force moving an object

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Kinetic and Potential Energy Stores

Anything that is moving has energy - kinetic energy stores

Energy transferred to this store - when an object speeds up and is transferred away as it slows down

Energy in kinetic energy store depends on object's mass and speed

Greater the mass and the faster it's going, the more energy there will be

Kinetic Energy = 1/2 x mass x speed^2

Lifting an object in a gravitational field requires work

Causes transfer of energy

Higher object is lifted, more energy is transferred to this store

Amount of energy in gpe depends on object's mass, it's height and strength

GPE = mass x gravity x height

When something falls, energy from its gravitational potential potential energy store is transferred to its kinetic energy store

For a falling object, there's no air resistance:

Energy lost from gpe store = energy gained in kinetic energy store

Air resistance acts against all falling objects

Causes some energy to be transferred to other energy stores

Stretching or squashing an object can transfer energy to its elastic potential energy store

As long as the limit of proportionality has not been exceeded - energy in the elastic potential energy store can be found

Elastic potential = 1/2 x spring constant x extension^2

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Specific Heat Capacity

Specific Heat Capacity - amount of energy needed to raise temperature of 1kg of a substance by one degree

Materials that need to gain lots of energy to warm up also transfer loads of energy when they cool down again - can store a lot of energy

Change in thermal energy = mass x shc x change in temp

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Conversation of energy and power

Energy can be transferred usefully, stored or dissipated, but never be created or destroyed

When energy is transferred, not all energy is transferred usefully

Some is always dissipated when an energy transfer takes place

Power is the rate of energy transfer/rate of doing work

Measured in watts

One watt = 1 joule of energy transferred per second

Power = energy transferred / time

Power = work done / time

Powerful machine isn't necessarily one that exerts a strong force

Power machine is one which transfers a lots of energy in a short space of time

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Reducing unwanted energy transfers

When something moves, there's usually at least one frictional force acting against it

Causes some energy to be dissipated

Lubricants can be used to reduce the friction between the objects' surfaces when they move

Lubricants are usually liquids so they can flow easily between objects and coat them

When an object is heated, energy is transferred to the kinetic energy stores of its particles

Causes particles to vibrate more and to collide with each other - energy is transferred between particles' kinetic energy stores - conduction

Thermal conductivity - measure of how quickly energy is transferred through a material this way

Materials with a high thermal conductivity transfer energy between particles at a faster rate

If particles are free to move

Particles moving faster means space between individual particles increases - causes density of the region being heated decrease

Liquids and gases can flow

Warmer and less dense region will rise above denser, cooler regions

So energetic particles move away from hotter to cooler regions convection

Few things you can do to prevent energy losses through heating

Have thick walls - material with low thermal conductivity

Thicker walls and lower thermal conductivity, slower the rate of energy transfer will be (building will cool more slowly)

Use thermal insulation:

Cavity walls - made up of an inner and outer wall with an air gap in the middle. Air gap reduces amount of energy transferred by conduction

Loft insulation - reduce convection current being created

Double- glazed windows - work in same way as cavity walls - air gap between two sheets of glass to prevent energy transfer by conduction

Draught excluders - around doors and windows reduce energy transfers by convection

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Efficiency

Useful devices are useful - can transfer energy from one store to another

Some of input energy is usually wasted by being transferred to useless energy store - usually a thermal energy store

Less energy that is wasted in this energy store, the more efficient device is

Can improve efficiency by insulating objects, lubricating them or making them more streamlined

Efficiency = useful energy transfer/total energy transfer

Efficiency = useful power output/total power input

For any given example you can talk about the types of energy being input and output, but remember: NO device is 100% efficient

Wasted energy is usually transferred to useless thermal energy stores

Electric heaters are the exception to this

Usually 100% efficient as all energy in the electrostatic energy store is usually transferred to "useful" thermal energy stores

Ultimately, all energy ends up transferred to thermal energy stores

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Energy Resources and Their Uses

Fossil fuels and nuclear fuel

Fossil fuels - natural resources that form underground over millions of years

Typically burnt to provide energy:

Coal

Oil

(Natural) Gas

Will run out one day

All do damage to the environment

Provide most of our energy

Renewable energy resources never run out

Most of them damage environment - less harmful than non-renewable

Don't provide much energy and some of them are unreliable - depend on weather

Non-renewable energy resources:

Petrol and diesel powered vehicles use fuel created from oil

Coal - used in old-fashioned stream trains to boil water to produce steam

Renewable energy resources:

Vehicles that run on pure bio-fuels or a mix of a bio-fuel and petrol or diesel (only bio-fuel is renewable)

Non-renewable resources:

Natural gas - most widely used fuel for heating homes in UK. Gas is used to heat water, which is then pumped into radiators

Coal is commonly burnt in fireplaces

Electric heaters - use electricity generated from non-renewable resources

Renewable resources:

Geothermal heat pump - geothermal energy resources to heat buildings

Solar water heaters - use the sun to heat water, them pumped into radiators

Burning bio-fuel/using electricity generated from renewable resources can also be used for heating

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Wind, Solar and Geothermal

Wind Power

Involves putting lots of wind turbines in exposed places

Each has a generator inside it - rotating blades turn generator and produce electricity

No pollution

Do spoil views - need about 1500 wind turbines to replace one coal- fired power station

Can be very noisy - can be annoying

Stop when wind stops or if wind is too strong

Impossible o increase supply when there's extra demand

Initial costs are quite high - no fuel costs and minimal running costs

No permanent damage to landscape

Solar cells

Generate electric currents directly from sunlight - often best source of energy to charge batteries

Often used in remote places and to power electric road signs and satellites

No pollution

Very reliable source - only in daytime

Solar power can still be cost-effective even in cloudy countries

Can't increase power output when there's extra demand

Initial costs are high - energy is free and running costs are low

Generally generates electricity on relatively small scale

Geothermal power

Possible in volcanic areas or where hot rocks lie quite near to surface

Source is slow decay of various radioactive elements

Brilliant free energy - reliable and does very damage to environment

Can be used to generate electricity/heat buildings directly

Aren't many suitable locations for power plants

Cost of building power plant is often high compared to amount of energy produced

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Hydro-electricity, waves and tides

Hydro-electric power

Requires flooding of valleys - to build large dams

Water is allowed out through turbines

No pollution

Big impact on environment - loss of habitat/look unsightly

Immediate response to increased demand for electricity

Initial costs are high - no fuel costs/minimal running costs

Useful way to generate electricity on a small scale in remote areas

Wave power

Lots of small wave-powered turbines around the coast

Moving turbines are connected to a generator

No pollution - disturbing the seabed, habitats of marine animals, spoiling views and being a hazard to boats

Fairly unreliable - waves tend to die out when wind drops

Initial costs are high - no fuel costs and minimal running costs

Wave power - never likely to provide energy on a large scale

Can be useful on small islands

Tidal Barrages

Big dams are built across river estuaries with turbines in them

As tide comes in, it fills up the estuary - water then allowed out through turbines at controlled speed

No pollution - prevents free access for boats, spoiling views and altering habitat

Height of tides are variable

Initial costs are moderately high

No fuel costs and minimal running costs

Can only be used in some of the most suitable estuaries

Potential for generating significant amount of energy

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Bio-fuels and Non-renewables

Bio-fuels

Are renewable energy resources created from either plant products or animal waste

Can be solid, liquid or gas - can be burnt to produce electricity or run cars in the same way as fossil fuels

Supposedly carbon neutral, although there's some debate about this as it only really true if you keep growing plants at the rate you're burning things

Bio-fuels are reliable - crops take relatively short time to grow and different crops can be grown all year round

Can't respond to immediate energy demands

Bio-fuels are fairly reliable

Crops take relatively short time to grow and different crops can be grown all year round

They can't respond immediate energy demands

To combat this bio-fuels are continuously produced and stored for when they're needed

Cost to refine bio-fuels is very high and some worry that growing crops specifically for bio-fuels will mean there isn't enough space or water to meet demands for crops

In some regions, large areas of forest have been cleared to make room to grow bio-fuels

Resulting in lots of species losing their natural habitats

Decay and burning of vegetation also increases CO2 and methane emissions

Non-Renewable

Fossil fuels and nuclear energy are reliable

Enough fossil and nuclear fuels to meet current demand

They're extracted from Earth fast enough so power plants always have fuel in stock

Means power plants can respond quickly to changes in demand

However, they're running out slowly

If no new resources are found, fossil fuels may run out

While set-up costs of power plants can be quite high compared to some other energy resources

Running costs aren't that expensive

Combined with fairly low fuel extraction costs

Using fossil fuels is cost effective when producing energy

Coal, oil and gas release CO2 into the atmosphere when they're burned

All this CO2 adds to greenhouse effect and contributes to global warming

Burning coal and oil also releases sulfur dioxide, which causes acid rain

Which can be harmful to trees and soils

And have far-reaching effects in eco-systems

Acid rain can be reduced by taking sulfur out before fuel is burned, or cleaning up emissions

Coal-mining makes a mess of the landscape

Especially "open-casting mining"

As with many energy resources, the view can be spoilt by power plants

Oil spillages cause serious environmental problems

Affecting mammals and birds that live in and around the sea

We try to avoid them, but they'll always happen

Nuclear power is clean

But is very dangerous and difficult to dispose of

Nuclear fuel is relatively cheap

But overall cost of nuclear power is high due to cost of power plant and final decommissioning

Nuclear power always carries the risk of a major catastrophe

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Trends in energy resource use

20th century

Electricity use of the UK hugely increased as population grew and people began to use electricity for more and more things

21st century

Electricity use has been decreasing as there more efficient appliances and people are more careful with energy use

Most of electricity is produced using fossil fuels and form nuclear power

Generating electricity isn't the only reason we burn fossil fuels:

Oil is used to fuel cars

Gas is used to heat homes and cook food

Trying to increase use of renewable energy resources

Move towards renewable energy resources has been triggered by many things

Burning fossil fuels is very damaging to the environment

Makes many want to use more renewable energy resources that affect environmental laws

People and governments becoming increasingly aware that non-renewables will run out

Many people think it's better to learn to get by without non-renewables

Pressure from other countries and public means governments have begun to introduce targets for using renewable resources

Puts pressure on energy providers to build new power plants - use renewable - make sure don't lose business and money

Car companies affected by this change in attitude towards environment

Electric cars and hybrids are already in use and popularity is increasing

Use of renewables is limited by reliability, money and politics

Lots of scientific evidence supporting renewables

Although scientists can give advice - they don't have power to make people, companies or governments change their behaviour

Building new renewable power plants costs money

Some energy providers are reluctant

As fossil fuels are cost effective

Cost of switching to renewable power will have to be paid ]

Either by customers in bills or governments and taxes

Some don't want to/can't afford to pay

Arguments about whether it's ethical to make them

Even if new power plants are built, there are arguments over where to put them

Arguments about whether it's ethical to make people put up with wind farms built next to them when they may not agree

Some energy resources aren't reliable as fossil fuels

Others can't increase power output

Would mean having to combine different power plants or researching ways to improve reliability

Research on improving reliability and costs takes time and money

May be years before improvements are made even with funding

Until then, we need dependable, non-renewable power

Making personal changes can be quite expensive

Hybrid cars are generally more expensive

Solar panels are expensive

Cost of these things is slowly going down - still aren't an option for many