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Energy Resources and Energy Transfer This section is about energy and energy resources. It has these parts in it: Energy basics Energy transfer diagrams Temperature and heat Transfer of thermal energy Non-renewable energy resources Renewable energy resources Saving energy Energy basics Energy allows things to happen. If you leap around wildly, people often say that you have lots of energy. Energy allows you to move around and keep warm. It allows you to see and to hear. Energy cannot be created out of thin air or destroyed - it can only be stored or transferred from place to place in different ways. Let's look at some examples. The vibrating drum and the plucked guitar string transfer energy to the air as sound. This sound energy can be transferred to your eardrum as kinetic energy (movement energy). The battery transfers stored chemical energy as electrical energy in the moving charges in the wires. The electrical energy is transferred to the surroundings by the lamp as light energy and thermal energy (heat energy). The rock on the mountain has stored energy because of its position above the ground and the pull of gravity. This energy is called gravitational potential energy. As the rock falls to the ground, the gravitational potential energy is transferred as kinetic energy. A cup of hot tea has heat energy in the form of kinetic energy from its particles. Some of this energy is transferred to the particles in cold milk, which you pour in to make the tea cooler. When the explosive goes off, chemical energy stored in it is transferred to the surroundings as thermal energy, sound energy and kinetic energy. Energy transfer diagrams Energy transfer diagrams show the locations of energy stores and energy transfers. For example, consider the energy transfers in the simple electrical circuit below. We can show the transfers like this: The battery is a store of chemical energy. The energy is transferred by electricity to the lamp, which transfers the energy to the surroundings by light. These are the useful energy transfers - we use electric lamps to light up our rooms. But there are also energy transfers that are not useful to us. In the example above, the lamp also transfers energy to the surroundings by heating. If we include this energy transfer, the diagram looks like this: Sankey diagrams Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved. The Sankey diagram for the lamp (below) shows that it transfers most of the energy by heating, rather than by light. Notice that the total amount of energy transferred to the surroundings is the same as the amount of electrical energy. We say that the energy has been conserved. Energy is always conserved, it is never "lost" or "wasted", although some energy transfers are useful and some are not. Temperature and heat Temperature and heat are not the same, although both are concerned with thermal energy. The temperature of an object is to do with how hot or cold it is, measured in degrees Celsius. Note that the unit of temperature is written as oC, not oc or oc. A thermometer is used to measure the temperature of an object The heat an object contains is the amount of its thermal energy, measured in joules or J. Let's look at two examples to see the difference between temperature and heat. A swimming pool at 30°C is at a lower temperature than a cup of tea at 80°C. But, the swimming pool contains more water, so it stores more thermal energy or heat than the cup of tea. To boil water, we must increase its temperature to 100°C. It takes longer to boil a large beaker of water than to boil a small beaker of water, because the large beaker contains more water and needs more thermal energy or heat to reach 100°C. The small beaker of water boils first Transfer of thermal energy Thermal energy can be transferred by: conduction convection radiation Thermal energy can also be transferred when a liquid evaporates. The liquid particles with the most energy leave the liquid and enter the surroundings. This is why your skin feels cold if you lick the back of your hand and blow over it gently. Conduction and convection also need moving particles to transfer thermal energy. Conduction Thermal energy can move through a substance by conduction. Substances that allow thermal energy to move easily through them are called conductors. Metals are good conductors of thermal energy. Substances that do not allow thermal energy to move through them easily are called insulators. Air and plastics are insulators. When a substance is heated, its particles gain energy and vibrate more vigorously. The particles bump into nearby particles and make them vibrate more. This passes the thermal energy through the substance by conduction, from the hot end to the cold end. This is why the handle of a metal spoon soon gets hot, as well as its rounded part, when the spoon is put into a hot drink. Convection The particles in liquids and gases can move from place to place. Convection happens when particles with a lot of thermal energy in a liquid or gas move, and take the place of particles with less thermal energy. Thermal energy is transferred from hot places to cold places by convection. Radiation All objects transfer thermal energy by radiation called infrared radiation. The hotter an object is, the more radiation it gives off. No particles are involved in radiation, unlike conduction and convection. This means that thermal energy transfer by radiation can even work in space, but conduction and convection cannot. Radiation is why we can feel the heat of the Sun, even though it is millions of kilometres away in space. The police use infrared cameras to track down criminals in the dark. Non-renewable energy resources Energy resources provide us with energy. There are different types of energy resource, including fuels such as coal or food, and stores of energy such as batteries or the wind. We can divide energy resources into two categories, non-renewable and renewable. Non-renewable energy resources cannot be replaced once they are all used up. Renewable energy resources can be replaced, and will not run out. Non-renewable: fossil fuels The fossil fuels are coal, oil and natural gas. They formed millions of years ago from the remains of living things. Coal was formed from plants, and oil and natural gas from sea creatures. When the living things died, they were gradually buried by layers of rock. The buried remains were put under pressure and chemical reactions heated them up. They gradually changed into the fossil fuels. You can find out more about this here Fossil fuels . Coal is a fossil fuel The fossil fuels are non-renewable energy resources. Once we have used them all up, they will take millions of years to replace, if they can be replaced at all. The energy stored in the fossil fuels originally came from sunlight. Plants used light energy from the Sun for photosynthesis to make their chemicals. This stored chemical energy was transferred to stored chemical energy in animals that ate the plants. When the remains of the plants and animals became fossil fuels, their chemical energy was stored in the fuels. The energy is transferred to the surroundings as thermal energy and light energy when the fuels burn. Renewable energy resources Renewable energy resources can be replaced, and will not run out. Take care: it is not true to say that they can be re-used. Renewable: biomass Biomass fuels are fuels from living things such as trees. Wood is a biomass fuel. As long as we continue to plant new trees to replace those cut down, we will always have wood to burn. Just as with the fossil fuels, the energy stored in biomass fuels ultimately came from the Sun. Renewable: wind power Wind is caused by huge convection currents in the Earth's atmosphere, driven by heat energy from the Sun. The moving air has huge amounts of kinetic energy, and this can be transferred into electrical energy using wind turbines. Wind turbines cannot work if there is no wind, or if the wind speed is high enough to damage them. A wind turbine Renewable: water power Moving water has kinetic energy. This can be transferred into useful energy in different ways. For example: wave machines use the up and down movement of waves to turn electricity generators tidal barrages are built across the mouths of rivers. As water moves in or out of the river mouth when the tide turns, the kinetic energy in the water is used to turn electricity generators. Hydroelectric power (HEP) schemes store water high up in dams. The water has stored gravitational potential energy. As the water rushes through pipes, this stored energy is transferred to kinetic energy, which turns electricity generators. An energy transfer diagram for an HEP scheme Saving energy Electricity can be generated in many ways, including: in power stations using fossil fuels or biomass fuel using wind turbines using hydroelectric power schemes using wave power or tidal power using solar cells. Most of the UK's electricity is generated in power stations using fossil fuels. Thermal energy released from the burning fuel is used to boil water to make steam, which expands and turns turbines. These drive the generators to produce electricity. As the fossil fuels are non-renewable energy resources, and they produce pollution when they burn, we are aiming to produce more of our electricity using renewable energy resources. This will reduce the rate at which the fossil fuels are used up. We can also reduce the rate at which the fossil fuels are used up by saving energy. For example, we can walk to school instead of getting a lift in a car. We can turn down the heating a bit and we can turn off the lights when we leave the room.