conservation of energy Flashcards
equation to calculate change in gravitational Potential energy when an object is raised above ground
change in GPE = m * g * change in h
joule kg n/kg m
equation to calculate the amounts of energy associated with a moving object
KE = 0.5 * m * v squared
Joule 0.5 kg speed squared
interpret diagrams to represent energy transfers
- boxes show stores
- arrows show transfers
(looks like box with energy store written, arrows showing way of transferring energy ((ex mechanically)), arrow goes to other energy transfers, ex kinetic energy -> mechanically -> thermal energy store of ball)
*can be more arrows and boxes
explain what is meant by conservation of energy
- energy can be stored, transferred between stores and dissipated
-BUT IT CAN NEVER BE CREATED OR DESTROYED - total energy in a closed system has no net change
Analyse the changes involved in the way energy is stored when
a system changes for an object projected upwards or up a slope
- ball works against gravitational force
- so energy transferred mechanically from kinetic energy store of ball
- to its gravitational potential energy store
Analyse the changes involved in the way energy is stored when
a system changes a moving object hitting an obstacle
ex bat hitting ball
- energy in kinetic energy store
- some energy transferred mechanically to ball’s kinetic energy store
- some energy is transferred mechanically to thermal energy stores of bat and ball (and surroundings by heating)
- rest carried away by sound
Analyse the changes involved in the way energy is stored when
a system changes an object being accelerated by a constant force
ex rock dropped from cliff
- assuming no air resistance, gravity works on rock, so rock constantly accelerates towards the ground
- energy transferred mechanically from rock’s gravitational potential energy store
- to its kinetic energy store
Analyse the changes involved in the way energy is stored when
a system changes a vehicle slowing down
(without braking)
- energy in kinetic energy store of car transferred mechanically (due to friction between tires and road)
- then by heating, to the thermal energy stores of the car and road
Analyse the changes involved in the way energy is stored when
a system changes bringing water to boil in an electric kettle
- energy transferred electrically from mains to heating element of kettle
- then by heating to the thermal energy store of water
Explain that where there are energy transfers in a closed
system there is no net change to the total energy in that system
- total energy in a closed system has no net change
because - closed system is a system (collection of objects) that can be treated on its own without any energy being exchanged to or from the surroundings
- if energy incr. or decr. its not closed
- you can make it into a closed system by incr. number of things you treat as part of it
ex pan of water heating on hob = not closed, but pan, gas and oxygen that burn to heat it and their surroundings are a closed system
Explain that mechanical processes become wasteful when they
cause a rise in temperature so dissipating energy in heating the
surroundings
- mechanical (force acting on object) work done means frictional forces need to be overcome
- ex moving parts rubbing together and air resistance
- energy needed to overcome frictional forces is transferred to thermal energy stores of whatever is doing the work and the surroundings
- this energy isn’t useful and so is dissipated
Explain, using examples, how in all system changes energy is
dissipated so that it is stored in less useful ways
- energy is only useful when it is transferred from one store to a useful store
- not useful energy gets dissipated (often to surroundings or thermal energy stores)
ex - - radio or speakers - electrical work is transferred into useful sound waves
- thermal energy is dissipated = rise in temperature (internal energy store) of the surroundings
ex - - tumble dryer - electrical work is transferred into useful internal (thermal) energy - helps dries clothes
- energy is dissipates wastefully by sound waves = rise in temperature of surroundings
*dissipated = energy is spread out so “lost”
Explain ways of reducing unwanted energy transfer
through lubrication
- lubrication reduces energy transferred by friction
- something moves = at least one friction force acting against it
- this transfers energy mechanically to thermal energy store of objects involves - then dissipated by heating to surroundings
- lubricants can be used to reduce friction between object’s surfaces when they move
- usually liquids like oil so they can flow easily between objects and coat them
Explain ways of reducing unwanted energy transfer
through thermal insulation
- insulation reduces rate of energy transfer by heating
- fabrics like wool and cotton are good insulators
- as usually low density or contain pockets of trapped air
- makes them effective as air is a poor conductor
- Surrounding a warm object with a material that contains trapped air will reduce the rate at which it loses heat
Likewise, surrounding a cold object with such a material will reduce the amount of heat reaching the object
Describe the effects of the thickness and thermal conductivity of
the walls of a building on its rate of cooling qualitatively
(qualitatively = good or bad something is )
- in a building the lower the thermal conductivity of its walls the slower the rate of energy transfer through them (building cools down slower)
- cavity walls with air gap in middle reduces amount of energy transferred by conduction as air has a low thermal conductivity
- thicker walls hep = slow energy transfer
what is thermal conductivity
how well a material transfers energy by conduction
ex metals = high thermal conductivity
gases (like air) = low thermal conductivity
recall efficiency equation
efficiency = (useful energy transferred by the device) (J) / (total energy supplied to the device) (J)
*if want percentage *100
explain how efficiency can be increased
- reduce energy wasted ex lubrication and thermal insulation
- decreasing amount of wasted energy = higher proportion of supplied energy is transferred to useful stores
(so efficiency of the process is increased)
Describe the main energy sources available for use on Earth: bio-fuel and sate adv/dis
- renewable
- created from either plant products or animal dung, can be solid liquid gas
- burnt to produce electricity or run cars in same way as fossil fuels
adv- carbon neutral if you grow plants at rate your burning things
- reliable, plants take short time to grow
dis- high cost
- demand for these crops might leave no room for food crops
- sometimes large areas of forest has been cleared to make room to grow them
Describe the main energy sources available for use on Earth: wind
- wind turbine has generator, wind rotates blade - turned generator = electricity
adv- no pollution
- running costs are minimal
dis- high initial costs
- lots needed to produce enough power
- can spoil view
- only work when windy, cant always supply electricity or respond to high demand
Describe the main energy sources available for use on Earth: hydro-electricity
- involves flooding valley or building dam
- rainwater is caught and goes through turbines
adv- no pollution
- immediately responds to increased electricity demand - more water can be let through
- low running costs
- reliable
dis- high costs
- impact on environment as flooding valley may destroy habitats
Describe the main energy sources available for use on Earth: tidal
- big dams across river estuaries with turbines
- tide comes in and fills up estuary- water let through turbines at controlled speed to generate electricity
adv- no pollution
- reliable
-no fuel costs and minimal running costs
dis- high initial costs
- height of tides is variable and barrages don’t work when the water level is the same either side
- can affect boat access
-spoil view
- alter habitat for wildlife ex wading birds
compare ways in which both renewable and non-renewable sources are used
-non-renewable = reliable, lots of energy, meet current demand. contributes to greenhouse effect, finite
- renewable = never run out- energy can be “renewed” as it’s used, most do no damage to environment or at least are less bad than non-renewables, don’t provide as much energy, unreliable and may depend on weather
Describe the main energy sources available for use on Earth: nuclear fuel
- nuclear power plants
adv- reliable
- meet current demand and can respond quickly to changes in energy demands (use more fuel to release more energy)
dis- high cost to build and safely decommission
- finite
- nuclear waste in dangerous and difficult to dispose of
Describe the main energy sources available for use on Earth: fossil fuels
- natural resources from underground that form over millions of years that are typically burnt to provide energy
- main = coal, oil, (natural) gas
adv- reliable
- still enough to meet current demand - respond quickly to changes in demand (use more fuel to release more energy)
- costs are low to extract and pretty cheap to build and run
dis- finite
- greenhouse effect - global warming
- can release sulfur dioxide - acid rain
- oil spillages
Describe the main energy sources available for use on Earth: sun
- solar cells are from materials that use energy transferred by light to create an electrical current
- often used in remote places where there’s not much choice and to power electric road signs and satellites
adv- no pollution
- basically no running costs
dis - high initial costs
- slightly unreliable depending on weather and time of day
- mainly used to generate electricity on a small scale
- can’t increase production when there’s extra demand
- (use quite a lot of energy to make)
Explain patterns and trends in the use of energy resources
-currently we still depends on fossil fuels - electricity in UK increased due to bigger population
- impact of fossil fuels has made science and society to develop the use of renewables
