Physics 9-1 GCSE AQA Energy
- 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
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
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
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
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.
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
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
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
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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