physics - energy

energy transfers + stores :

• stores :

  • kinetic energy

  • gravitational potential energy

  • thermal energy

  • chemical energy

  • elastic potential energy

• transfers :

  • mechanical

    • to move object through a distance

  • electrical

    • when charge flows (electricity)

  • heating

    • energy transferred between hotter and colder regions

  • radiation

    • energy transferred as a wave e.g light

conservation of energy - energy cannot be created or destroyed

sankey diagrams - represent the flow of energy visually by identifying energy stores, transfers and points where it could be wasted

conduction, convection and radiation

conduction : main method of energy transfer in solids

• occurs when two solids of dif temp come into contact and energy is transferred from thermal store of hotter object to thermal store of colder object

• energy is transferred through vibration of atoms

• metals contain free electrons/delocalised electrons

convection : main energy transfer in fluids

• the heat source heatssurrounding fluid particles

• particles gain energy in kinetic store so move faster and further apart so become less dense

• further away from heat source the particles cool and become more dense so fall back down towards heat source

• convection current can move cold or hot fluids

radiation : main energy transfer in form of waves or particles

• all objects emit infrared radiation

• hotter object = more infrared radiation emited

• black matt objects are best emitters and absorbers + when next to heat, would heat up quicker than a lighter object

• shiny objects are worst emitters and absorbers

convection in everyday life

• boiling water

  • heat passes from burner into pot, heating water from top to bottoms

• radiator

  • puts warm air out top and draws cooler air in at the bottom

• ice melting

  • heat moves to the ice from the air

• steaming cup of tea

  • steam is showing heat being transferred into the air

reducing unwanted energy transfer

• insulation

  • creates a barrier between hot and cold object that reduces heat transfer by either reflecting thermal radiation or decreasing thermal conduction and convection from one object to another

• wall insulation

• double glazing windows

  • space between panes creates an air gap that slows down thermal transfer by conduction

• floor insulation

work done = energy transferred

work done = kinetic energy - gravitational potential energy

conservation of momentum in a pendulum

• at top of swing, it has the highest GPE (furthest from earth) and the lowest KE (as it slows to a stop)

• at the bottom of the swing, it has the lowerst GPE (closest to earth) and the highest KE (swings very quickly at this part)

  • energy is being conserved; its constantly changing between different forms, and the only reason why energy is lost from the pendulum making it slow down is because some energy is converted into heat or sound

  • 

energy transfers involved in generating electricity using:

• wind

  • wind turbines

    • wind turns the propeller-like blades of a turbine around a rotor, which spins and generator, which creates electricity

• water

  • hydropower

    • water flows through a pipe/penstock

    • spins the blades in a turbine

    • spins generator

    • creates electricity

• geothermal resources

  • reservoirs of hot water that exist or are humandmade at varying temperatures and depths below the earth’s substance

• solar heating system

  • when this material is exposed to photons of sunlight (very small packets of energy) it releases electrons and produces an electric charge

• solar cells

  • when the sun shines onto a solar panel, energy from the sunlight is absorbed by the PV cells in the panel

  • this energy creates electrical charges that move in respone to an intenral electrical field in the cell

  • causes electricity to flow

• fossil fuels

  • fossil fuels are burned to produce energy

    • they are burned in the presence of oxygen

    • as the fuel burns, the heat energy is used to heat water, as it is heated it produces steam which in turn rises and drives a turbine

• nuclear power

  • heat produced during atomic fission to boil water and produce pressurized steam

  • steam is routed through the reactor steam system to spin large turbines blades that drive magnetic generators to produce electricity

advantages and disadvantages of methods of large-scale electricity production from various renewable and non-renewable resources:

advantages :

• renewable energy sources like the sun, wind and water is that they will never run out

disadvantages :

• non - renewable resources are not only finite

  • cost more as their availability declines and requaire more extreme extraction methods with greater environmental impacts