Energy stores and transfers Flashcards
system
an object or a group of objects
object in equilibrium
nothing changes and so nothing happens
change to an object
energy is transferred
kinetic
moving objects have energy
gravitational
objects gain energy in their gravitational potential store as they are lifted above ground
elastic
objects have energy in their elastic potential store if they are streched
electostatic
objects with charge interacting with one another have energy in their electrostatic store
magnetic
magnetic interacting with each other
chemical
objects with energy in their chemical store can release energy
nuclear
atomic nuclei release enrgy from their nuclear store during reactions
thermal
all objects have energy in their thermal store, the hotter the object the more energy it contains
energy pathways
mechanical
electrical
heating
radiation
mechanical working
when a force acts on an object
electrical working
a charge moving through a potential differencee
heating by particles
energy is transferred from a hotter object to a colder one
heating by radiation
energy transferred by EM waves
principle of conservation of energy
energy cannot be created, or destroyed it can only be transferred from one store to another
total amount of energy=
closed system
remains constant
efficiency
the ratio of the useful energy output from a system to its total energy output
system with high efficiency
most of the energy transferred is useful
effieciency equation
efficiency= (useful energy output/total energy output) x 100%
sankey diagrams
used to represent energy transfers
left hand side sankey diagram
represents the energy transferred into the system
straight arrow in sankey diagram
the useful energy output
bended arrow in sankey diagrams
wasted energy
total energy in equation
useful energy out + wasted energy
how is energy transferred by heating and radiation
conduction
convection
radiation
how is energy from a mug of hot coffee transferred
through radiation from the surface of the mug to the surroundings due to the infrared radiation being emitted from its surface
until when do objects continue to lose heat
until they reach thermal equialibrium
what are good conductors
metals
what are poor conductors called
insulators
what happens when a substance is heated
atoms start to move around and vibrate more, as they bump into each other transferring energy from atom to atom
why are metals good at conducting heat
due to delocalised electrons which collide with the atoms, helping to transfer the vibrations through the material.
convection
thermal energy transferred through liquids and gases
convection current explain
- molecules push apart, fluid expands
- makes hot fluid less dense than surroundings
- hot fluid rises and cool fluid moves in to take place
- hot fluid cools and sinks back down
the more hotter the object=
the more infrared radiation it radiates
what colour is the best abosrber and emitter
black
what objects are the worst emitting and absorbing thermal radiation
shiny
how do you reduce conduction
use materials with low thermal conductivity (insulators)
reduce convection
currents need to be prevented from forming.
- fluid that forms the current has to prevented from moving
what reduces energy transfers from conduction and convection
insulation
what does the effectiveneness of a insulator depend on
- thermal conductivity of material
- density of material
- thickness of material
what is insulation made of
fibre glass
why is glas fibre a good insulation
- air is trapped between the fibres which makes is a good insulator
cavity wall insulation
gaps or cavities between external walls being filled with insulation.
how is work done
when an object is moved over a distance by a force applied in the direction of its displacement
energy transferred is equal to
work done
equation for work done
W ( J)= F x d (m)
GPE
the energy an object has due to its height in a gravitational field
equation for G.P.E
G.P.E= mass x graviational field strength (N/kg) x height (m)
what is the gravitational field strength of the earth?
10 N/kg
why is it easier to life a mass on the moon
its gravitational field strength is less
when is it harder to lift mass more than on earth
on bigger planets
kinetic energy
the amount of energy an object has as a result of its mass and speed
equation for kinetic energy
K.E= 1/2 X m x V^2
V is speed of the object
why are pendulums an example of perfect energy trasnfers
all of the energy in the kinetic store is transferred mechanically to its gravitational potential store
power
the rate of the energy transfer or the rate of work done
equation for power
Power (W) = Word done/ time
reneweable energy
an energy source that is replenished at a faster rate than the rate at which it is being used
examples of renewable energy
solar energy, wind, bio fuel, hydroelectricity, geo thermal, tidal
turbine
turned which turns a generator which generates electricity
how can water be used to turn turbines
energy in the K store of the flowing water is transferred to the K store of the turbine and then to the K store of the generator which is trans electrically to the national grid.
what can fossil fuels be used to turn turbines?
fossile fuels combusted to heat water which produced steam to turn it
how can nuclear fuels be used to produce electricity
- nuclear fuels are used to heat water to produce steam to turn it
- nuclear store -> thermal store of water -> kinetic store of turbine -> kinetic store of generator
advantages of reneweable energy
- reliable as it won’t run out
- sometimes not reliable such as wind energy
pros and cons of fossiul fuels
- reliable and can produce a large amount of energy
- produces GHG and pollution
pros and cons of nuclear energy
- reliable and doesn’t pollute
- produces radioactive waste that takes thousands of years to decay
pros and cons of hydroelectricity energy
- reliable and can produce large amounts of energy
- flooding large areas, destroy wildlife
pros and cons of wind energy
- no GHG, no pollution
- not reliable, turbines are ugly and noisy
