physics - conservation of momentum (3.1 - 3.14)

3.1 GPE equation

change in grav. potential energy (J) = mass (kg) x grav. field strength (N/kg) x change in height (m)

ΔGPE = mgΔh

3.2 kinetic energy equation

kinetic energy (J) = ½ x mass (kg) x speed² (m/s)²

KE = ½mv²

3.3 diagrams to represent energy transfers

3.4 conservation of energy

energy cannot be created/destroyed, only transferred from one store → another

total energy transferred by system = energy put into system

3.5 changes in energy stores - object projected upwards

energy in object (kinetic) —transferred mechanically→ energy in object (GPE)

3.5 changes in energy stores - moving object hitting obstacle

energy in moving object (kinetic) —transferred mechanically→ energy in object & obstacle (thermal & sound)

3.5 changes in energy stores - object accelerated by constant force

energy in moving object (kinetic) —transferred mechanically→ energy in moving object (kinetic)

3.5 changes in energy stores - vehicle slowing down

energy in moving vehicle (kinetic) —transferred by forces (braking)→ energy in hot brakes (thermal)

3.5 changes in energy stores - boiling water in electric kettle

energy in kettle (thermal) —transferred by heating→ energy in water & surroundings (thermal)

3.6 energy transfers in closed system

no net change to total energy in system - energy is conserved

3.7 mechanical processes - wasteful

moving parts touch → causes friction → rise in temperature

thermal energy in hot machine transferred to surroundings by heating - dissipates energy

energy can’t be used for other useful energy transfers - wasted

3.8 energy dissipated in all system changes

energy not always transferred into useful forms, stored in less useful ways

e.g. kettle - energy stored in hot water = useful, energy stored in kettle & surroundings = not useful

3.9 reducing unwanted energy transfer - lubrication

reduces friction between moving parts

conduction

vibrations passed on between particles in solid

convection

warmer part of fluid rises & sets up convection current

radiation

only way energy transferred through vacuum

infrared radiation can pass through gases & some solids

3.9 reducing unwanted energy transfer - thermal insulation

decreases rate of energy transfer by heating

low thermal conductivity = energy not transferred easily by heating

materials containing air are good insulators - air has low thermal conductivity

trapped air cannot form convection currents - doesn’t transfer much energy

3.10 effects of thickness & thermal conductivity of walls of building on rate of cooling

to decrease rate of energy transfer:

• increase thickness

• decrease thermal conductivity

• decrease temperature difference

3.11 efficiency equation

3.12 how can efficiency be increased?

reduce amount of wasted energy

mechanical processes - reduce friction

ensure all fuel put into engine is burned

use energy transferred by heating (otherwise wasted)

3.13 fossil fuels

store lots of energy

easy to store & use in engines

non-renewable

burning fossil fuels release CO₂ & other gases

• CO₂ - contributes to climate change

• other gases - contribute to pollution

expensive to reduce pollution

3.13 nuclear fuel

store lots of energy in small piece of material

useful for spacecraft - mass of fuel is important

don’t emit gases

non-renewable

produces radioactive waste

expensive to dispose of radioactive waste

expensive to decommission nuclear power station

major accident can have serious consequences

3.13 bio-fuel

renewable

used in same way as fossil fuels

made from animal wastes/any part of plants

carbon neutral - when burned, release same amount of CO₂ as took from atmosphere growing

energy needed to grow, harvest & turn crops into fuel - not carbon neutral

uses lots of land

3.13 wind

renewable

wind turbines generate electricity (if wind not too fast/slow)

need lots of wind turbines to produce same amount of energy as fossil-fuelled power station

some think they spoil landscape

not always available - depend on wind speed

3.13 hydro-electricity

renewable

falling water (trapped in high reservoirs) generates electricity

always available

can be started & stopped very quickly

3.13 the tides

renewable

tidal power generates electricity - turbines in barrage across river estuary turn as tides flow in & out

available at predictable times

not always available

not many places in UK suitable for barrages

may affect birds & other wildlife that live/feed on tidal mudflats

3.13 the sun

renewable

solar cells generate electricity - convert solar energy directly into electrical energy

not always available - depend on sun

3.14 patterns & trends in use of energy resources