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Energy (Heat capacity (If needs lots of energy to warm up they transfer a…
Energy
Heat capacity
If needs lots of energy to warm up they transfer a lot when cool (they can store a lot)
diffrent materials have diffrent capacities
specific heat capacity = energy to get temputure of 1kg by 1º
triangleE = mctrianglehomes
pratical???
efficiency
often energy is wasted on transfer i.e. to a thermal energy store
efficiency = useful power output total input energy
efficiency is a product output / input
measured in watts
useful energy input isn't normal = to total energy output
energy stores and systems
Energy stores
theremal
kinetic
GPE (gravitatatinal potential energy)
elastic potential
chemical
magnetic
electrostatic
nuclear
transfered
electrically
heating
macanicaly
radiation
light
sound
system changes
A system is a fancy word for single, group
can be open or closed
closed - matter can neither enter or leave
methods of transfer
heating
doing work
conservation of energy and power
transferred, never created / destroyed
example
open system - Useful transferred chemical energy from battery to phone but some thermal energy dissipates to heat
closed system - cold spoon in hot soup flask, spoon hat energy transfers to spoon (isles thermal energy)
power (W)
power = energy/time
power = work done/time
power = watts
kenetic and potential energy (J)
Kenetic
Ek = 1/2 mv2
mass = kg
v = m/s2
potential
GPE = mgh
mass = Kg
g = N/kg
h = m
9.8 = GPE
GPE = J
EPG
elastic potential energy
Ee = 1/2ke2
k = spring constant (N/m)
e = extension (m)
conduction and convection (heating)
convection
particles move away from hotter to colder regions
can happen in gasses and liquids
transfer by heating store
conduction
vibrating particles transferring energy to neighbouring particles
high thermal conductivity
transfer energy quickly between particles
solids
examples
radiator - energy transferred to air by conduction (air particle collide with radiator), warm air rises, goes away from radiator, cools then goes back to radiator, cycle repeats = convection current
reducing unwanted energy transfers
thermal insolation
house - thick walls with low thermal conductivity material
lubrication
reduce frictional force (i.e. prevent dissipation from genetic to thermal energy store)
examples
cavity walls, loft insulation, double glass windows, draft excluder
check units are the same