p1 - energy

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  • p1 - energy
    • gravitational potential energy
      • Ep = mgh
      • amount of energy in a g.p.e store depends on an objects mass, height and the strength of its gravitational field
      • when an object falls, energy from its gravitational potential energy store is transferred to its kinetic energy store
    • elastic potential energy
      • Ee = 1/2 ke²
      • as long as the limit of proportionality has not been exceeded, energy is transferred to the elastic potential energy store
      • stretching or squashing an object can transfer energy to its e.p.e store
    • kinetic energy
      • Ek = 1/2 mv²
      • anything that is moving has energy in its kinetic energy store
      • energy in the store depends on the mass and speed of this object, the greater the mass and speed, the more energy in its store
    • conservation of energy and power
      • energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
      • a mobile phone is a system. When being used, energy is usefully transferred from the chemical energy store of the battery to the phone. This is why your phone feels warm after being used
      • a closed system is a physical system that does not allow the transfer of matter in or out of the system
      • rate of energy transfer, or the rate of doing work
      • power is measured in watts, one watt = one joule of energy transferred per second
      • P = E/t or P = W/t
    • efficiency
      • useful output/total input
      • useful power output/total lower output
      • the less energy 'wasted', the more efficient the device
    • energy transfers
      • lubrication reduces frictional forces
        • when something moves, there is usually at least one frictional force acting against it
          • causes some energy to be dissipate, so lubricating, like oil, helps objects to move more smoothly
      • heating can occur by conduction and convection
        • materials with a higher thermal conductivity transfer energy between their particles at a faster rate
          • energy particles move from hotter to cooler regions - convection
        • when energy is transferred tot he kinetic energy stores of the particles, so the particles vibrate more and collide more - conduction
      • insulation reduces the rate of energy transfer by heating
        • 1. thick walls with low thermal conductivity
        • the thicker the walls, the slower the transfer of energy
        • 3. some houses have cavity walls, made up of an inner and outer wall with a gap in between them - sometimes filled with insulating foam
        • 4. loft insulation reduces convection currents
        • 5. double-glazed windows reduce conduction
        • 6. draught excluders around doors and windows reduce convection
    • energy resources
      • renewable     - solar, wind, waves, hydro-electric, bio-fuel, tides, geothermal - never run out - do damage but not as much
      • non-renewable     - coal, oil, gas - will eventually run out -  damage the environment - provide most of our energy
      • used for heating
        • natural gas for water, coal in fireplaces, geothermal, electric heaters to heat homes, solar water heaters
      • used for transport
        • petrol and diesel from oil, coal is used for steam trains, some run on biofuels, or a mix with petrol
    • types of power
      • wind power involves lots of turbines in exposed places - no pollution but they do spoil the view. Needs 1500 turbines to replace 1 coal station. They rely on wind. Initial costs are high but have minimal running costs. No permanent damage
      • solar cells generate electricity from sunlight, often in remote places. There is no pollution. Reliable but only in daylight. Initial costs are high but there are almost no running costs
      • geothermal power uses underground thermal energy stores. This is possible in volcanic areas or where hot rocks lie quite near to the surface. Reliable energy, that does little damage to the environment. However, there aren't many suitable locations and costs are high
      • non-renewables are reliable and there is enough to meet demand. However, they are slowly running out. Initial costs are high, but running costs are not as expensive.
      • water power requires flooding valleys by dams, small wave powered turbines, or tidal barriers. Wave powers are fairly unreliable, as waves die out when there is no wind. Initial costs are high but they all have minimal running costs
      • biofuels are created by plant products or animal dung. It is fairy reliable but costs are high
    • specific heat capacity
      • amount of energy needed to raise the temperature of 1kg of a substance by 1°C
      • ?E = mc??
      • some materials need more energy to increase their temperature than others
        • water requires 4200J to heat by 1°C, but mercury only needs 139J
      • practical
        • 1. have a block of the material with 2 holes in it
        • 2. measure the mass of the block, then wrap it in an insulating layer to reduce the energy transferred from the block to the surroundings
        • 3. insert the thermometer and heater and turn on the power
        • 4. as the block heats up, take readings of the temperature and current every minute for 10 minutes
        • 5. calculate the power supplied using P=VI, then calculate energy transferred to the heater using E=Pt
        • 6. plot a graph of the results
        • 7. find the gradient of the graph ??=?E
        • 8. specific heat capacity = 1 / (gradient x mass of block)
        • 9. repeat with different materials

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