Energy
- Created by: Jmsmcn
- Created on: 14-09-17 17:01
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- Energy
- Energy stores and systems
- Energy is transferred between stores
- The stores are: Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, and nuclear
- Energy can be transferred mechanically, electrically, by heating, or by radiation
- Whrn a system changes energy is tranfered
- A system is a word for an object or group of objects you are interested in
- In a kettle energy is transferred from the heating element to water by heating
- Work done is another way of saying energy tranfered
- When a person throws a ball up chemical energy in the arm transfers to kinetic energy in the ball
- Energy is transferred between stores
- Kinetic and potential energy stores
- Movement means energy in an object's kinetic energy store
- Energy is transferred to the store when it speeds up and away from the store when it slows down
- The amount of energy in the store depends on the mass and speed
- Kinetic Energy = 0.5 X mass X VELOCITY^2
- Raised objects store energy in gravitational potential energy
- Liftign an object in a gravtional filed requires work
- Energy is transferred to the store when the item is raised up
- The amount of nice of G.P.E depends on the mass, the height, and the gravitational field strength
- G.P.E = mass X gravitational field strength X height
- When an object falls energy from the G.P.E store is transferred to kinetic energy
- In real life air resistance causes some energy to be transferred to thermal energy stores
- Energy lost from G.P.E store = Energy gained in kinetic energy store
- Stretching or squashing an object can transfer energy to elastic potential enegry stores
- Elastic potential energy = 0.5 X spring constant X extension
- This applies if the limit of proportionality has not been exceeded
- Elastic potential energy = 0.5 X spring constant X extension
- Movement means energy in an object's kinetic energy store
- Conservation of energy and power
- Energy can be transferred, stored, or dissipated but never created or destroyed
- Not all energy is transferred usefully, some energy is dissipated
- This is often called wasted energy
- In a closed system no energy leaves the system so there is always a net change of zero
- Power is the rate of doing work (1 watt is 1 joule per second)
- Power = Energy transferred / Time
- A powerful machine means it can convert energy quickly
- Conduction and convection
- Conduction is the process where vibrating particles transfer energy to neighboring particles
- The particles in the object that are being heated vibrate more and collide with others
- These collision cuase energy to be transfred between particles
- This continues until the heat is evenly distributed
- These collision cuase energy to be transfred between particles
- Thermal conductivity is a measure of how quickly energy is transferred in this way
- The particles in the object that are being heated vibrate more and collide with others
- Convection is where energetic particles move away from hotter to colder regions
- This happens in gases and liquids as the particles can move
- When you heat a region the particles move fsater and the distnce between the particles increases this reduces the density
- The less dence region will then rise up taking the heat with it
- When you heat a region the particles move fsater and the distnce between the particles increases this reduces the density
- Radiators create convection currents
- This happens in gases and liquids as the particles can move
- Conduction is the process where vibrating particles transfer energy to neighboring particles
- Reducing unwanted energy transfer
- Lubrication reduces friction
- When something moves there is always friction which causes energy to be wasted (usually to heat)
- Lubricants reduce the friction so things can flow easier
- Lubricants are usually liquids like oil
- Insulation reduces the rate of energy transfer
- You don't want energy to escape outside as you have to put more energy in to keep it warm
- Thicker walls and walls with a lower thermal conductivity slow the rate of energy loss
- Cavity wall insulation (reduces energy transfer by convection), loft insulation (reduces convection currents)
- Double glazed windows (prevent loss by conduction), draft excluders (reduce convection)
- Lubrication reduces friction
- Efficiency
- Most energy transfers involve some waste energy
- Devices are useful as they transfer energy between stores, but some is wasted and the less that is wasted the more efficient the device is.
- You can improve efficiency by insulating, lubricating, or making something more streamlined
- Efficiency = useful output/total power input
- Useful output is not usually equal to input
- Wasted energy is usually transferred to thermal energy stores.
- However electric heaters are usually 100% efficient as all the energy is transferred to heat.
- Ultimately all energy ends up as heat
- Most energy transfers involve some waste energy
- Energy resources
- Non-renewable energy sources will run out
- They are fossil fuels (coal, gas and oil) and nuclear fuel (uranium and plutonium)
- They damage the environment but provide most of our energy
- Renewable energy resources will never run out
- Solar, wind, waves, tides, HEP, bio-fuel, geothermal
- Most of them damage the environment but in less nasty ways then fossil fuels
- They don't provide much energy and many are unreliable
- Energy resources can be used for transport
- Petrol and diesel are used in cars, coal is used in steam trains
- Some vehicles run on bio-fuels, or petrol/diesel and bio-fuels
- They can be used for heating
- Natural gas is used to heat water and it is then pumped into radiators (most common fuels for heating in the UK)
- Coal is used in fire places, electric heaters generally use electricity from nonrenewable sources.
- Geothermal is used to heat buildings, solar water heaters use the sun to warm water, bio-fuels can be used fro electricity in electric heaters
- Non-renewable energy sources will run out
- Wind, Solar and Geothermal
- Wind-power involves putting up lots of wind turbines in exposed (windy places)
- Each turbine has a generator that is turned by the blades.
- There is no pollution (except when they are made)
- They spoil the view and can be very loud
- Around 1,500 are needed to replace 1 coal fired power station but that uses a lot of land.
- If the wind stops there is no power and you cannot produce more if there is high demand
- They produce electricity roughly 75%-80% of the time
- The initial costs are quite high but there are minimal maintenance costs
- There is no permanent damage
- Solar Cells
- They use the sun's energy to generate electric currents
- It is used in remote places when there are no other electricity sources
- No pollution (energy is used to make them)
- It can be reliable in sunny countries (only in the day)
- This makes it cost efficient
- Generally used on a small scale as it is cheap
- High initial costs low running costs
- Geothermal power
- Can bue used in volcanic areas, or areas with hot rocks nesar the surface
- Most of the energy is because of the decay of radioactive elements in the earth.
- It is reliable and does little damage
- It can be used to generate electricity or to heat buildings directly
- There are high startup costs and not many suitable locations
- Can bue used in volcanic areas, or areas with hot rocks nesar the surface
- Wind-power involves putting up lots of wind turbines in exposed (windy places)
- Bio-fuels and non-renewables
- Bio-fuels are made from plants and water
- They are brunt to produce electricity or they can be used in cars in similar ways to fossil fuels
- Burning them produces CO2 but growing them absorbs it
- They are quite reliabel but cost a lot of money
- Some areas of woodland have be removed to farm bio-fuels which destroyes habitats
- Fossil fuel are reliable as there is a large supply
- They are slowly running out
- Set up costs are high but running costs are low
- They are bad for the enviroment
- CO2 emissions contribute to the greenhouse gas effect
- Sulfur dioxide causes acid rain
- Coal mining ruins the landscape
- Oil spills can kill animals
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- Bio-fuels are made from plants and water
- HEP, Waves and Tides
- Hydroelectric power uses falling water to generate power
- A big dam is built and a reservoir is made, water is allowed out via a turbine
- There us a big impact because of the flooding
- Rotting vegetation produces carbon dioxide and methane
- Loss of habitat and villages
- Dry reservoirs can look very unsightly
- It can provide a response to increased demand
- Initial costs are high but there are low running costs
- Unreliable if there is a drought
- Wave power uses wave-powered turbines
- The turbines turn a generator which produces electricty
- There is no pollution but it may disturb the sea bed, marine animals (and their habitats, and be a hazard to boats
- It can be an eyesore
- They are quite unreliable and initial costs are high but there are no running costs
- Tidal barrages use the sun's and moon's energy
- A tidal barrage is the most common way to use tides
- A dam is built across a river estuary and water is allowed in, water is then allowed out through turbines
- There is no pollution but it prevents access for boats and animals.
- It is reliable but the height of the tides changes so neap tides will produce less energy
- Iniral costs are quite high but running costs are very low and it can produce a lot of electcity
- A tidal barrage is the most common way to use tides
- Hydroelectric power uses falling water to generate power
- Trends in resource energy use
- We rely on fossil fuels
- Energy use went up but it is now going down as appliances become more efficient
- We use them for electricity, to fuel cars and heat homes
- People want to use more renewable resources
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- We rely on fossil fuels
- Specific Heat Capcity
- More energy need to be transferred to different things to raise its temperature
- Materials that need lots of energy to heat up release lots of energy as they cool
- Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1C
- Change in thermal energy = mass X specific heat capacity X temperature change
- Energy stores and systems
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