Energy (Energy stores and systems (When energy transferred to object,…
Energy stores and systems
When energy transferred to object, energy stored in energy store:
Energy is transferred mechanically (doing work), electrically (work done by moving charges), heating or radiation.
System- single object or group of objects. When system changes, energy is transferred into or away from system between different objects in system or between different types of energy stores.
Closed system- neither matter or energy can enter or leave. Net change in total energy of closed system=0.
Kinetic and potential energy stores
Energy transferred to kinetic when object speeds up and transferred away when object slows down.
Lifting object in gravitational field requires work- transfer of energy to g.p.e store of raised object.
When something falls, energy from g.p.e transferred to kinetic. Energy lost from g.p.e store= energy gained from kinetic.
Stretching or squashing an object can transfer energy to elastic potential energy store. So long as limit of proportionality has not been exceeded, energy in elastic potential can be found:
Reducing unwanted energy transfers
When something moves, at least 1 frictional force acting against it- some energy dissipated. Lubricants used to reduce friction- liquids that can flow easily between objects and coat them.
When object heated, energy transferred to kinetic energy stores of particles. Causes particles to vibrate more and collide with each other. Collisions cause energy to transfer between particles kinetic energy stores- conduction.
Thermal conductivity - measure of how quickly energy is transferred through a material. Materials with high thermal conductivity transfers energy between particles at faster rate.
If particles free to move, particles move faster so space between individual particles increase. Causes density of region being heated to decrease. As liquids and gases flow, warmer and denser regions will rise above denser, cooler regions. Energetic particles move away from hotter to cooler regions- convection.
Prevent energy losses through heating:
Thick walls made from material with low thermal conductivity- slower rate of energy transfer.
Thermal insulation- cavity walls made of inner and outer wall with gap- air gap reduces energy transferred by conduction through walls.
Cavity wall insulation gap filled with foam - reduce energy transfer by convection.
Loft insulation- reduce convection currents being created in lofts.
Double glazed windows- air gap between 2 sheets of glass to prevent energy transfer by conduction.
Draught excluders- reduce energy transfers by convection.
Bio-fuels and non-renewables
Biofuels- renewable energy resource from plant products or animal dung- solid, liquid or gas- burned to produce electricity or run cars. Carbon neutral. Reliable as crops take short time to grow and different crops can be grown all year round. But do not respond to immediate demands- continuously produced and stores.
The cost to refine biofuels is high and can mean there isn't space or food and water to meet crop demands. Can mean large forests cleared- loss of natural habitats. Decay and burning of vegetation- CH4 and CO2 emissions.
Fossil fuels and nuclear energy is reliable- able to meet current demand; extracted fast enough to keep in stock- responds quickly to demand. Running out. High initial cost but cheap running. Cost effective but release CO2 into atmosphere when burned- greenhouse effect and global warming. Sulfur dioxide; acid rain- harmful to trees, soil and ecosystems. Acid rain can be reduced by taking sulfur out before burning or cleaning up emissions.
Coal mining- mess of landscapes. Oil spillages- environmental issues. Nuclear power- clean but waste is dangerous and difficult to dispose of. Nuclear fuel cheap but overall cost of power is high due to power plant cost and final decommissioning.
Energy resources and uses
Non-renewable; fossil fuels and nuclear fuel (uranium and plutonium). 3 main fossil fuels= coal, oil and natural gas. Will run out, do damage to environment and provide most of our energy.
Renewable; Sun, wind, water waves, hydro-electricity, bio-fuel, tides, geothermal. Never run out, do damage but less than non-renewable- don't provide much energy and some unreliable as depend on weather.
Can be used for transport: petrol and diesel powered, coal; steam trains. Bio-fuels or mix with petrol and diesel.
Used for heating: natural gas to heat water that is pumped around radiators, coal for fires, electric heaters from non-renewable energy resources. Geothermal heat pump to heat buildings, solar water heaters. Burning bio-fuel or use electricity generated from renewable resources.
Wind, solar and geothermal
Wind-turbines in exposed places. Each turbine has generator- rotating blades turn generator and produce electricity. No pollution but spoil view- 1500 needed to replace 1 coal fired power station. Cover a lot of ground. Noisy. Relies on wind and problem if too strong wind. May not replenish extra demand. Produce electricity 70-85% of time. High initial costs but no fuel cost and minimal running cost. No permanent damage to landscape.
Solar cells generate electric current from sunlight- best source for small material which don't use much electricity (calculator). Used in remote places and power electric road signs and satellites. No pollution; little in manufacture. Reliable in sunny countries- only in daylight. Can't increase power output when extra demand. High initial cost but then free and minimal running cost.
Geothermal- volcanic areas or hot rocks near surface. Energy from slow decay of radioactive elements (uranium) deep inside Earth. Free, reliable and little damage to environment. Generate electricity or heat buildings directly. Not enough suitable locations and cost to build power plant is higher than energy produced.
Hydro-electricity, waves and tides
Hydro-electricity- flooding of valley by buildings dam. Water allowed out through turbines. No pollution. Big impact on environment (rotting vegetation releases CH4 and CO2) and loss of habitat for species. Putting power stations in remote areas reduces impact on humans. Can provide immediate response to increase in demand. Reliable except in drought. High initial costs but no fuel costs and minimal running costs. Useful in remote areas on small scale.
Wave- lots of small wave-powered turbines located around coast. Moving turbines connected to generator. No pollution. Disturbs seabed and habitat of marine animals, spoil view and hazard to boats. Unreliable as waves die out when wind drops. High initial costs but no fuel costs and minimal running costs. Useful on small islands.
Tidal barrage- big dams built across river estuaries, with turbines. As tide comes in, fills up estuary and then through turbine at controlled speed. Tides produced by gravitational pull of Sun and Moon. No pollution. Prevents free access by boats, spoils view and altering habitat of wildlife. Reliable as tides happen at least twice a day near to predicted height- height is variable so lower tides provide less energy than big ones. Don't work when water level is same as either side of barrage- happen 4x a day. Moderately high initial costs. No fuel costs and minimal running costs. Can provide significant amount of energy.
Conservation of energy and power
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed- conservation of energy.
Power- rate of energy transferred or rate of doing work. 1 watt = 1 joule of energy transferred per second.
Powerful machine= one which transfers a lot of energy in a short space of time.
The less energy wasted, the more efficient a device is. Improve efficiency of energy transfers by insulating objects, lubricating or making streamlined.
Electric heaters exception- 100% efficient as all energy in electrostatic energy store is transferred to useful thermal energy stores.
Trends in energy resource use
Since 21st century, electricity use in UK has been decreasing- more efficient appliances. Most produced by fossil fuels and nuclear plant to generate electricity. oil- fuel cars. Gas- heat homes.
People try to take care of environment so reduce non-renewable usage. Also use less as know will run out- find alternatives. Electric and hybrid cars. Building renewable power plants costs money so reluctant to change as fossil fuels cost effective. Minimal space for power plans. Some energy resources e.g. wind power- not as reliable as fossil fuels and cannot increase power output on demand; so use variety of power plants; expensive. Research- improving reliability- time and expense.So use dependable non-renewable. Personal changes can be expensive- hybrid cars and solar panels- expensive.
Specific heat capacity
Specific heat capacity- raising 1 kg of a substance by 1 degrees.
Different materials have different specific heat capacities. Materials that need to gain lots of energy in thermal energy store to warm up, also transfer lots of energy when cool down- can store a lot of energy.