Physics 1

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Energy Stores and Systems

System= object/ group of objects

Changes in the way energy is stored when a system changes:

-object projected upwards

-moving object hitting obstacle

-object accelerated by constant force

-vehicle slowing down

-bringing water to a boil in an electric kettle

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Changes in Energy

Equation for kinetic energy(energy of a moving object):

kinetic energy= 0.5 x mass x (speed) squared

Equation for elastic potential energy (energy stored in stretched spring):

elastic potential energy= 0.5 x spring constant x (extension) squared

Equation for gravitational energy (energy gained by an object raised above ground level):

g.p.e.= mass x gravitational field strength x height

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Energy Changes in System

Equation of temperature (amount of energy stored in/ released from a sysetm as temp changes:

change in thermal energy= mass x specific heat capacity x temp change

The specific heat capacity of substance= amount of energy required to raise temp of 1kg of substance 1 degree celsius

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Power

Power= rate energy transferred/ rate work is done

-power= energy transferred/time

-power= work done/time

Energy transfer of 1J per sec= power of 1W

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Energy Transfers in a System

Energy is transferred usfully, stored or dissipated (cannot be destroyed or created)

Energy transfers in a closed system= no net change to total energy

Higher thermal conductivity of a material = higher rate of energy transfer by conduction

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Efficiency

Energy efficiency for energy transfer equation:

efficiency= useful output energy transfer/ total input energy transfer

Another equation:

efficiency= useful power output/ total power input

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National and Global Energy Resources

Main resources are:

fossil fuels, nuclear fuel, biofuel, wind, hydro-electricity, geothermal, tides, the sun & water waves

Renweable resources= can be replenished as it is used

Energy used for:

-transport

-heating

-electricity generation

-heating

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