Physics 9-1 GCSE AQA Energy

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  • Created by: Will Lang
  • Created on: 10-11-17 17:20

Potential energy

When a spring is stretched, it stores energy

Potential energy = the amount of energy that is stored in an object

The spring stores potential energy

gravitational potential energy = energy stored in an object due to its position above ground

gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

Ep = mgh

elastic potential energy (J) = 0.5 x spring constant (N/m) x extension^2 (m)

Ek = 0.5 x ke^2

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Kinetic energy

energy must be transferred to objects to make them move

greater mass or speed = more energy transferred to kinetic energy store

kinetic energy = energy of a moving object

kinetic energy (J) = 0.5 x mass (kg) x velocity^2 (m/s)

Ek = 0.5mv^2

dropping an object transfers energy from gravitational potential energy store to kinetic energy store

when the object bounces, energy is transferred back to gravitational potential energy store

it does not bounce back up to its original height because some energy was lost to the surroundings

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Work done and energy transfer

work done = a force moving an object

increase in force applied = increase in work done

increase in displacement of object = increase in work done

work done (J) = force (N) x distance moved (m)

W=Fs

work done can change the kinetic energy stores of an object

work is done to reduce the kinetic energy of a car so that it stops

there is a force of friction between the brakes and the wheels

work done against friction causes the temperature of the brakes to increase as thermal energy is transferred to the brakes

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Understanding power

power = the rate of energy transfer or the rate of work done

more powerful machines transfer more energy per second

more powerful machines do more work

1W = 1J/s

power (W) = work done (J) / time (s)

P = W / t

power (W) = energy transferred (J) / time (s)

P = E / t

work done on an object = energy transferred to an object

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Specific heat capacity

different materials need different amounts of energy to raise the temperature of it by a given amount

amount of energy needed depends on objects mass, material and temperature change required

heating = transferring thermal energy

temperature = measure of how hot or cold an object is

specific heat capacity if the amount of energy needed to rais the temperature of 1Kg of an object by 1 degree C

change in thermal energy (J) = mass (Kg) x specific heat capacity (J/kgdegrees C) x temperature change (degrees C)

assume that the decrease in thermal energy stores of one object = the increase in thermal energy stores of the object that energy is transferred to.

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Dissipation of energy

lubrication = oiling moving parts of a machine to reduce friction so less thermal energy is wasted

thermal insulation = wrapping an object in insulating material that is a poor thermal conductor less less energy is transferred from it

buildings are insulated to keep them warm

trapped air reduces energy loss by conduction and convection but not by radiation

decrease in thermal conductivity of an object = decrease in energy transfer from the object

increase in thickness of insulation = decrease in energy transfer from the object

total energy in a closed system is always constant because energy is never created or destroyed

wasted energy = energy transferred to a store where it cannot be used

dissipates = enegry spreads out during a transfer

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Energy efficiency

not possible for useful energy to be greater than the total energy

not all energy is stored or transferred usefully

some energy always dissipates (thermal waste, sound waste etc)

reduces amount of energy that is usefully transferred

efficiency (%) = useful energy output / total energy input (x100)

law of conservation of energy = enegry cannot be created or destroyed, just transformed from one form to another

in a closed system, the input energy = the output energy

conservation of energy = no net change to the total energy of a system

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Using energy resources

electrical appliances convert electrical energy into different stores to serve the purpose of that particular aplliance

fossil fuels - non renewable - coal, oil and gas - will run out

wind - renewable - wind turns a turbine - not always available

wave - renewable - waves turn a turbine - not always available

solar - renewable - sun heats water - not always available

geothermal - renewable - hot rocks heat water - only available in certain countries

hydroelectric - renewable - falling water turns a turbine - spoils the environment

nuclear - non renewable - splitting an unstable atom - radioactive waste is dangerous for years

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Global energy supplies

increase in population = increase in energy demand = increase in energy consumption

fuel burning power stations (coal) releases carbon dioxide (global warming) and sulphur dioxide (acid rain)

nuclear power station waste reamins radioactive for hundreds of years and must be stored underground to reduce risk of radioactive contamination of the surrounding environment

nuclear power stations are dangerous in the event of a core meltdown

energy resources can be preserved

use them as efficiently as possible

reduce unwanted energy transfers from a particular applaince/generator

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