Energy Stores and Systems
- When energy is transferred to an object, the energy is stored in one of the object's energy stores
- Some of the energy stores are: thermal energy stores, kinetic energy stores, GPE stores, EPE stores, chemical energy stores, magnetic energy stores, electrostatic energy stores and nuclear energy stores.
- A system is a single object or a group of objects that you are interested in
- When a system changes, energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy stores.
- Closed systems = systems where neither matter nor enrgy can enter or leave (the net change in total energy of a closed system is always 0)
- Energy can be transferred either by heating or by doing work
- E.g. energy is transferred to water by heating, into the water's thermal energy stores
- Work done basically means energy transferred and it can be done when current flows or by an object being moved by a force
- E.g. a ball is dropped and gravity does work and causes energy to be transferred from the ball's gravitational potential energy store to its kinetic energy store
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Kinetic and Potential Energy Stores
- If an object is moving, it has a kinetic energy store and energy is transferred to this store when an object speeds up and is transferred away from the store if it slows down
- The greater the mass and the faster its going, the more energy there will be in the KE store
- Lifting an object in a gravitational field requires work, which causes an energy transfer to the GPE store of the raised object. The higher it is lifted, the more energy is transferred
- When something falls, energy from its GPE store is transferred to its KE store
- For a falling object without air resistance : energy lost from GPE store = energy gained in KE store
- Air resistance acts against all falling objects and causes some energy to be transferred to other energy stores
- Stretching or squashing an object can transfer energy to its EPE store
- KE = 1/2mv^2
- GPE = mgh
- EPE = 1/2ke^2
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Specific Heat Capacity
- More energy needs to be transferred to the thermal energy stores of some materials to increase the temperature than others (e.g. you need 4200J of warm 1kg of water by 1 degree)
- These materials that need to gain lots of energy in their thermal energy stores to warm uo also transfer loads of energy when they cool back down (i.e. they can store a lot of energy)
- Specific heat capactiy is the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree.
- Change in Thermal Energy = m x c x change in θ
- Change in thermal energy measured in joules (J)
- m = mass measured in kg
- Specific heat capacity measure in J/kg degree celsius
- Temperature change measured in degrees celsius
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Conservation of Energy
- "Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed."
- When energy is transferred between stores, not all of it is transferred usefully into the store you want it to go in to. Some enrgy is dissipated when an energy transfer takes place.
- Dissipated energy basically means wasted energy because the energy is stored in a way that isn't useful (usually into the thermal stores)
- E.g. when you use your phone, energy is usefully transferred from the chemical energy store of the battery. However some of this energy is dissipated to the thermal energy store (when your phone gets warm)
- E.g. if you drop a cold spoon into a flask of hot soup and put a lid on it, you expect that the flask is a perfect thermal insulator so, the spoon and flask are now a closed syste. Energy transfers from the soup's thermal energy store to the useless thermal energy store of the spoon (so the soup cools down a bit). Energy transfers have occurred, but no energy has left the system, therefore the net change in energy is 0.
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Reducing Unwanted Energy Transfers
- Whenever an object moves, there is usually a frictional force acting on it, which causes some energy int he system to be dissipated (e.g. air resistance can tranfer energy from a falling object's KE store to the thermal energy store)
- To reduce the friction between two objects rubbing together, lubrication can be added (usually liquids, so they can flow easily between objects)
- When an object is heated, there is an energy transfer to the KE stores of its particles, which causes the particles to vibrate more frequently and to collide more. During these collisions, energy transfers occur between the particle's KE stores. This is called conduction.
- Thermal conductivity is a measure of how quickly energy transfers occur through a material this way. If a material has a high thermal conductivity, they will transfer energy at a faster rate.
- When particles are free to move the fast-moving particles mean that the space between individual particles increase, causing the density of the region to decrease.
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- Efficiency is a measure of how good a device is at changing energy from one form to another. The more efficient it is, the less wasted energy there is.
- Some ways of improving efficiency include: insulation, lubrication and streamlining.
- Efficiency = useful output energy / total input energy
- Efficiency can be given as a decimal or a percentage
- No device is 100% efficient and wasted energy generally goes to the thermal energy stores
- Electric heaters are the exception because they are usually 100% efficient due to all of the electrostatic energy in the energy store being transferred to useful energy stores
- All energy ends up transferred to thermal energy stores (e.g. in a drill energy is transferred to lots of different stores but it quickly ends up in the thermal energy stores.
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- Non-Renewable energy is energy that will eventually run out and includes fossil fuels and nuclear fuels .
- Fossil fuels form underground over millions of years and are usually burnt to supply energy for us. The main forms of this is: coal, oil and natural gas
- They will all run out one day and all do damage to the environment, however they do provide most of our energy
- Renewable energy is energy that will never run out and still do damage to the environment, but on a smaller scale than fossil fuels. However, they don't supply much energy and some are unreliable due to weather-dependency.
- Renerwable energy resources are: solar, wind, waves, hydro-electric, bio-fuel, tidal and geothermal
- Transport is obviously one of the largest users of fuel. Most cars a run with petrol and diesel (created from oil) and sometimes coal is used for trains. A renewable way to run vehicles is by using bio-fuels or a mix of bio-fuel and petrol.
- Heating uses natural gas largely and coal is used in fire places. A renewable way to run this would be by either using solar water heaters or a geothermal hand pump.
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Types of Renewable Energy Resources 1
- Hydroelectricity comes from rivers by transferring kinetic energy from the rivers into electrical energy by building a dam for the water to continually flow through. This is renewable, has no pollution and you can store water up high and away for whenever you need it. However, it costs a lot of money to build a dam and the dam also ruins the natural environment as you sometimes have to flood a section of land and you change the course of the water.
- Tidal Energy comes from the sea tides by transferring the water's GPE into electrical energy when the tide's high. At high tide, the water gets trapped behind a dam and when low tide comes around, water is released and generates energy. It is renewable and releases no pollution, however it costs a lot to build a dam and can cause local flooding
- Solar energy comes from the sun as the heat and light from the sun are either turned into electrical energy by solar cells or used to heat water for homes. It is renewable and nothing gets burned so, there is no pollution. However, solar panels and cells are expensive and weather-dependent.
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Types of Renewable Energy Resources 2
- Wave Energy comes from waves as the KE from the waves is transferred into electrical energy for the home with the help of machines that bob up and down in the water. This is renewable and has no pollution. However, you need a lot of machines which can be costly and it can also look ugly and are at risk of being damaged by storms.
- Wind Energy is from the wind by using wind turbines to turn KE into electrical energy. It is renewable, has no pollution and is quite cheap so, can be used worldwide. However, they can look ugly and be noisy and only works when windy.
- Biomass Energy is energy from plants as chemical potential energy is turned into heat energy by burning them. It is renewable (if we keep replanting) and doesnt need special equipment and doesnt add to greenhouse effect. However, large areas of land are needed to grow trees.
- Geothermal Energy is from the Earth as the heat energy from the Earth's rocks turn into electrical energy. Its renewable and doesnt damage the environment. However, there are very few places to be able to do this in the world and it costs a lot of money to drill underground.
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