Apuntes
Physics summer exam overview notes
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Energy
Types of energy:
chemical, heat, light, kinetic or movement, potential or stored, electrical, sound...
system is an object or group of objects
changes in the way energy is stored when a system changes
Changes in energy:
kinetic energy of a moving object: kinetic energy=0.5 x mass x speed squared
kinetic energy=Ek=joules=J
mass=m=kilograms=kg
speed=v=metres per second=m\s
elastic potential energy stored in a stretched spring: elastic potential energy=0.5 x spring constant x extension squared
elastic potential energy=Ee=joules=J
spring constant=k= newtons per metre= n\m
extension=e=metres=m
gravitational potential energy gained by another object raised above ground level: g.p.e=mass x gravitational field strength x height
gravitational potential energy=Ep=joules=J
gravitational field strength= g=newtons per kilograms=N\kg
height=h=metres=m
Energy changes in systems: the amount of energy stored or released from a system as its temperature changes=
change in thermal energy= mass x specific heat capacity x temperature change
change in thermal energy= AE=joules=J
specific heat capacity=c=joules per kilogram per degree celsius=J\kg degree celsius
the specific heat capacity of s substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius.
power: power is defined as the rate at which energy is transferred or the rate at which work is done.
power=energy transferred\time
power=work done\time
power=P,watts, W
energy transferred=E=joules=J
time=t=seconds
work done=W=joules=J
An energy transfer of 1 joule per second is equal to a power of 1 watt
Energy transfers in a system: energy can be transferred stored or dissipated NOT created nor destroyed.
the higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
efficiency:
efficiency= useful output energy transfer \ total input energy transfer
efficiency= useful power output\ total power input
national and global energy resources
main energy resources available for use on earth include: fossil fuels which is coal oil and gas, nuclear fuel, bio fuel, wind, hydroelectricity, geothermal, the tides, the sun and water waves.
a renewable energy resource is one that is being replenished as it is used
uses of energy resources include: transport, electricity generation and heating
wasted energy:
sometimes energy is wasted which means that some of the energy is transformed into types that are not useful. this energy is often in the form of sound and heat and it goes on to become dissipated or spread out.