Energy

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  • Created by: Jmsmcn
  • Created on: 14-09-17 17:01
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  • Energy
    • Energy stores and systems
      • Energy is transferred between stores
        • The stores are: Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, and nuclear
      • Energy can be transferred mechanically, electrically, by heating, or by radiation
      • Whrn a system changes energy is tranfered
        • A system is a word for an object or group of objects you are interested in
      • In a kettle energy is transferred from the heating element to water by heating
      • Work done is another way of saying energy tranfered
        • When a person throws a ball up chemical energy in the arm transfers to kinetic energy in the ball
    • Kinetic and potential energy stores
      • Movement means energy in an object's kinetic energy store
        • Energy is transferred to the store when it speeds up and away from the store when it slows down
        • The amount of energy in the store depends on the mass and speed
        • Kinetic Energy = 0.5 X mass X VELOCITY^2
      • Raised objects store energy in gravitational potential energy
        • Liftign an object in a gravtional filed requires work
        • Energy is transferred to the store when the item is raised up
        • The amount of nice of G.P.E depends on the mass, the height, and the gravitational field strength
        • G.P.E = mass X gravitational field strength X height
        • When an object falls energy from the G.P.E store is transferred to kinetic energy
          • In real life air resistance causes some energy to be transferred to thermal energy stores
          • Energy lost from G.P.E store = Energy gained in kinetic energy store
      • Stretching or squashing an object can transfer energy to elastic potential enegry stores
        • Elastic potential energy = 0.5 X spring constant X extension
          • This applies if the limit of proportionality has not been exceeded
    • Conservation of energy and power
      • Energy can be transferred, stored, or dissipated but never created or destroyed
      • Not all energy is transferred usefully,  some energy is dissipated
        • This is often called wasted energy
      • In a closed system no energy leaves the system so there is always a net change of zero
      • Power is the rate of doing work (1 watt is 1 joule per second)
        • Power = Energy transferred / Time
        • A powerful machine means it can convert energy quickly
    • Conduction and convection
      • Conduction is the process where vibrating particles transfer energy to neighboring particles
        • The particles in the object that are being heated vibrate more and collide with others
          • These collision cuase energy to be transfred between particles
            • This continues until the heat is evenly distributed
        • Thermal conductivity is a measure of how quickly energy is transferred in this way
      • Convection is where energetic particles move away from hotter to colder regions
        • This happens in gases and liquids as the particles can move
          • When you heat a region the particles move fsater and the distnce between the particles increases this reduces the density
            • The less dence region will then rise up taking the heat with it
        • Radiators create convection currents
    • Reducing unwanted energy transfer
      • Lubrication reduces friction
        • When something moves there is always friction which causes energy to be wasted (usually to heat)
        • Lubricants reduce the friction so things can flow easier
        • Lubricants are usually liquids like oil
      • Insulation reduces the rate of energy transfer
        • You don't want energy to escape outside as you have to put more energy in to keep it warm
        • Thicker walls and walls with a lower thermal conductivity slow the rate of energy loss
        • Cavity wall insulation (reduces energy transfer by convection), loft insulation (reduces convection currents)
        • Double glazed windows (prevent loss by conduction), draft excluders (reduce convection)
    • Efficiency
      • Most energy transfers involve some waste energy
        • Devices are useful as they transfer energy between stores, but some is wasted and the less that is wasted the more efficient the device is.
        • You can improve efficiency by insulating, lubricating, or making something more streamlined
        • Efficiency = useful output/total power input
      • Useful output is not usually equal to input
        • Wasted energy is usually transferred to thermal energy stores.
        • However electric heaters are usually 100% efficient as all the energy is transferred to heat.
        • Ultimately all energy ends up as heat
    • Energy resources
      • Non-renewable energy sources will run out
        • They are fossil fuels (coal, gas and oil) and nuclear fuel (uranium and plutonium)
        • They damage the environment but provide most of our energy
      • Renewable energy resources will never run out
        • Solar, wind, waves, tides, HEP, bio-fuel, geothermal
        • Most of them damage the environment but in less nasty ways then fossil fuels
        • They don't provide much energy and many are unreliable
      • Energy resources can be used for transport
        • Petrol and diesel are used in cars, coal is used in steam trains
        • Some vehicles run on bio-fuels, or petrol/diesel and bio-fuels
      • They can be used for heating
        • Natural gas is used to heat water and it is then pumped into radiators (most common fuels for heating in the UK)
        • Coal is used in fire places, electric heaters generally use  electricity from nonrenewable sources.
        • Geothermal is used to heat buildings, solar water heaters use the sun to warm water, bio-fuels can be used fro electricity in electric heaters
    • Wind, Solar and Geothermal
      • Wind-power involves putting up lots of wind turbines in exposed (windy places)
        • Each turbine has a generator that is turned by the blades.
        • There is no pollution (except when they are made)
        • They spoil the view and can be very loud
          • Around 1,500 are needed to replace 1 coal fired power station but that uses a lot of land.
        • If the wind stops there is no power and you cannot produce more if there is high demand
          • They produce electricity roughly 75%-80% of the time
        • The initial costs are quite high but there are minimal maintenance costs
        • There is no permanent damage
      • Solar Cells
        • They use the sun's energy to generate electric currents
        • It is used in remote places when there are no other electricity sources
        • No pollution (energy is used to make them)
        • It can be reliable in sunny countries (only in the day)
          • This makes it cost efficient
        • Generally used on a small scale as it is cheap
        • High initial costs low running costs
      • Geothermal power
        • Can bue used in volcanic areas, or areas with hot rocks nesar the surface
          • Most of the energy is because of the decay of radioactive elements in the earth.
        • It is reliable and does little damage
        • It can be used to generate electricity or to heat buildings directly
        • There are high startup costs and not many suitable locations
    • Bio-fuels and non-renewables
      • Bio-fuels are made from plants and water
        • They are brunt to produce electricity or they can be used in cars in similar ways to fossil fuels
        • Burning them produces CO2 but growing them absorbs it
        • They are quite reliabel but cost a lot of money
        • Some areas of woodland have be removed to farm bio-fuels which destroyes habitats
      • Fossil fuel are reliable as there is a large supply
        • They are slowly running out
        • Set up costs are high but running costs are low
        • They are bad for the enviroment
          • CO2 emissions contribute to the greenhouse gas effect
          • Sulfur dioxide causes acid rain
          • Coal mining ruins the landscape
          • Oil spills can kill animals
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    • HEP, Waves and Tides
      • Hydroelectric power uses falling water to generate power
        • A big dam is built and a reservoir is made, water is allowed out via a turbine
        • There us a big impact because of the flooding
          • Rotting vegetation produces carbon dioxide and methane
          • Loss of habitat and villages
          • Dry reservoirs  can look very unsightly
        • It can provide a response to increased demand
        • Initial costs are high but there are low running costs
        • Unreliable if there is a drought
      • Wave power uses wave-powered turbines
        • The turbines turn a generator which produces electricty
        • There is no pollution but it may disturb the sea bed, marine animals (and their habitats, and be a hazard to boats
          • It can be an eyesore
        • They are quite unreliable and initial costs are high but there are no running costs
      • Tidal barrages use the sun's and moon's energy
        • A tidal barrage is the most common way to use tides
          • A dam is built across a river estuary and water is allowed in, water is then allowed out through turbines
        • There is no pollution but it prevents access for boats and animals.
        • It is reliable but the height of the tides changes so neap tides will produce less energy
        • Iniral costs are quite high but running costs are very low and it can produce a lot of electcity
    • Trends in resource energy use
      • We rely on fossil fuels
        • Energy use went up but it is now going down as appliances become more efficient
        • We use them for electricity, to fuel cars and heat homes
      • People want to use more renewable resources
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    • Specific Heat Capcity
      • More energy need to be transferred to different things to raise its temperature
      • Materials that need lots of energy to heat up release lots of energy as they cool
      • Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1C
      • Change in thermal energy = mass X specific heat  capacity X temperature change

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