energy

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energy stores

Energy stores: thermal. kinetic. gravitational potential. elastic potential, chemical, magnetic, electrostatic and nuclear.

When a system changes energy is transferred into or away from the system, between different objects or between different types of energy stores.

In closed systems energy can't enter or leave. The net change in the total energy in a closed system is always 0 because no energy is being lost or gained.

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Work done

Work done is basically energy transferred.

Work is done when: current flows or a force moves an object.

When something is dropped from a height it is accelerated by gravity so the gravitational force does work.

if there is no air resistance on a falling object:

energy lost from the g.p.e = energy gained in the kinetic store

Air resistance acts on all falling objects in real life and it causes some energy to be transferred to other energy stores 

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kinetic and potential energy stores

Any moving object has energy in it's kinetic energy store. When an object speeds up energy is being transferred into the store and when it slows down energy is transferred away. The greater the mass and speed of an object the more energy in the kinetic energy store.

 kinetic energy = 1⁄2 × mass × speed²

Lifting an object transfers energy into the gravitational potential energy store. The higher an object is lifted the more gravitational potential energy it has. The amount of energy depends on the object's mass, the height and the gravitational field strength (10N/kg on earth) 

gravitational field strength = mass × gravitational field strength × height

stretching or squashing an object transfers energy into the elastic potential energy store as long as the limit of proportionality has not been overreached.

elastic potential energy = 1⁄2 × spring constant × extension²

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specific heat capacity

Specific heat capacity is the amout of energy required to heat 1kg of a substance by 1°c.

materials gain energy in their thermal energy store to warm us and lose energy from their thermal store to cool down. 

change in thermal energy = mass x specific heat capacity x temperature change

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Required practical- specific heat capacity

  • get a block of a solid material with two holes in it
  • mesure the mass of the block
  • cover it in an insulating layer to reduce the energy transferred into the surroundings
  • insert the thermometer and heater into the two holes in the material
  • measure the initial temperature
  • make the potential difference at the power supply 10V and start the stopwatch
  • the current does work on the heater transferring energy electrically from the power supply to the heaters thermal energy store. It is then transferred to the materials thermal store.
  • measure the temperature every minute
  • the current on the ammeter should not change
  • once 10 readings are collected turn the power suppply off

power = potential difference x current

you can calculate the power and energy

energy = power x time 

specific heat capacity = 1÷(gradient x the mass of the block)

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conservation of energy

conservation of energy principle - energy can be transferred usefully, stored or transferred out. Some energy is always dissipated when an energy transfer takes place, it is sometimes called wasted energy. 

Power is the rate of doing work. power is measured in watts

one watt = 1 joule of energy transferred per second

power = energy transferred / time

power = work done / time

something that is powerful transfers a lot of energy in a short space of time

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conduction

Conduction - vibrating particles in a a solid transfer energy to neighbouring particles.

  • When heated energy is transferred to the thermal energy store of the object, the energy is transferred to kinetic energy in the particles 
  • The particles in the part of the object that is being heated vibrate more and collide more frequently. The collisions cause energy to be transferred between the particles kinetic energy stores. This is conduction.
  • This continues through the rest of the object until the whole object is heated, the energy is then transferred to the surroundings or other objects touching it. 
  • Thermal conductivity measures how quickly energy is transferred through a material. A high thermal conductivity transfers energy quickly between particles
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convection

Convection is where energetic particles move away from hotter to cooler regions in liquids and gases.

when you heat the liquid or gas the particles move faster and the space between individual particles increases, decreasing the density of the reigon being heated. As the particles are free to move the less dense region will rise and will be replaced by the cooler regions. The heated particles cool when they have risen to the top and fall back down as they become more dense. if the heat source is constant a convection current is created.

a convection current is basically a the cycle of the convection process explained above.

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reducing unwanted energy transfers

Lubrication

whenever something moves there is at least one frictional force acting upon it, this causes some of the energy to be dissapated. lubricants (usually liquids) can be used to reduce the friction between two objects being rubbed together so that they flow easily along eachother.

Insulation

  • thick walls made made from a material with a low thermal conductivity- a slower rate of energy exchange
  • cavity walls- an inner and outer wall with a gap of air in between them as air is a very poor conductor of heat so less heat enters/ leaves
  • loft insulations- fibreglass wool is a good insulator as it has pockets of air in it. Prevents convection currents from forming, reduces energy loss by conduction
  • double glazed windows- have an air gap between the two sheets of glass to prevent conduction
  • draught exluders reduce energy transfers by convection
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Required practical- investigating energy transfers

  • boil water and put into a sealable container (a beaker and a lid) 
  • measure the mass of water in the container
  • measure the initial temperature of the water
  • seal the container and leave it for 5 minutes timed on a stopwatch
  • remove the lid and measure the final temperature
  • pour out the container and allow it to cool to room temperature 
  • repeat using the same mass of water but wrap the container in different materials

you could also test the thickness of the material rather than different materials

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energy resources

non-renewable energy resources - nuclear fuel and fossil fuels.

  • These will all run out one day, finite resources
  • do damage to the environment
  • provide most of our energy

Three main fossil fuels: Coal, oil, natural gas

renewable energy resources- the sun(solar), wind, water waves, hydro-electricity, bio-fuels, tides, geothermal.

  • never run out and can be renewed as it's used 
  • do less damage to the earth than non-renewable energy resources
  • don't provide much energy and unreliable if depending on the weather
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uses of renewable and non renewable energy resourc

transport

non renewable:

  • petrol and diesel powered vehicles use fuel created from oil
  • coal in old fashioned steam trains to boil water to make the steam

renewable:

  • vehicles run on pure biofuels or a mix of biofuels and petrol or diesel(only the biofuel part is renewable)
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uses of renewable and non renewable energy resourc

heating

non renewable:

  • natural gas used to heat water which is pumped in radiators throughout houses
  • coal burnt in fireplaces

renewable:

  • solar water heaters use the sun to heat water which is pumped through radiators
  • burning biofuel or using electricity generated from renewable resources can be used for heating
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wind power

  • each turbine has a generator inside it, the rotating blades turn the generator to produce electricity
  • no pollution except when it's being manufactured
  • 1500 are needed to replace one coal fired power station so they take up a lot of space 
  • very noisy may be inconveniencing for people that live by them
  • when wind stops the turbines or if the wind is too strong they stop
  • produce electricity 70-85% of the time
  • initial costs are high but no fuel costs and minimal running cost
  • no permenant damage as if removes the scenery will go back to how it was
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solar cells

  • best to charge batteries in things like watches and calculators which do not use much electricity
  • used in remote places where there is not much choice and to power electric road signs and satellites
  • no pollution( some in the production of the cells)
  • very reliable in sunny countries but only at daytime 
  • can't increase the power output when there is an increased demand
  • initial costs are high but after that cost basically nothing
  • generate electricity on a small scale
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geothermal power

  • only possible in volcanic areas where hot rocks are near to the surface. the source of the energy is the slow decay of radioactive elementsm including uranium
  • free energy that is reliable
  • can generate electricity or heat buildings directly
  • there aren't many suitable locations for power plants and the cost is very high compared to the amount of energy it produces
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hydro-electric power

  • no pollution
  • floods a valley by creating a big dam which allows rainwater through the turbines
  • possible loss of habitat for some species 
  • rotting vegetation releases methane and carbon dioxide
  • putting them in remote valleys reduces the effect they have upon humans
  • cam provide immediate response to an increase in demand
  • no problems with reliability unless theres a drought
  • initial costs are hig but running costs are minimal
  • generate electricity on a small scale in remote areas
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water power

  • loads of small wave powered turbines around the coast, the moving turbines are connected to a generator
  • no pollution
  • disrupt the seabeds and the habitats of marine animals
  • unreliable as waves drop with the wind
  • initial costs are high low running costs
  • useful on small islands
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tidal barrages

  • big damd built across river estuaries with turbines in them
  • as the tide comes in it fills up the estuary, the water is allowed through the turbines at a controlled speed
  • tides are produced at the gravitational pull of the sun and moon
  • no pollution
  • prevents free access by boats
  • reliable as tides happen twice a day
  • the height of tides is variable so the amount of electricity produced daily would be inconsistent
  • initial high cost but cheap to run
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bio-fuels

bio-fuels- renewable energy resources made from plant products or animal waste. They can be solids, liquids, or gases.

pros

  • carbon neutral, as carbon is being used it is being reproduced so the amout of carbon it uses is equal to the amount of carbon that is produced
  • reliable, take a relatively short time to grow crops

cons

  • costs are very high
  • people fear that growing crops for biofuels will reduce the space and water used to grow food
  • forests are cleared to make space to grow biofuels, so lots of species lose their natural habitats
  • decay and burning vegetation increases carbon dioxide and methane emmissions
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non-renewable resources

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