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Station 1: Mechanical Energy The concept of energy was first introduced in the chapter States of Matter, where it is defined as the ability to cause change in matter. Energy can also be defined as the ability to do work. Work is done whenever a force is used to move matter. When work is done, energy is transferred from one object to another. For example, when the batter in Figure below uses energy to swing the bat, she transfers energy to the bat. The moving bat, in turn, transfers energy to the ball. Like work, energy is measured in the joule (J), or newton·meter (N·m). It takes energy to swing a bat. Where does the batter get her energy? Energy exists in different forms, which you can read about in the lesson “Forms of Energy” later in the chapter. Some forms of energy are mechanical, electrical, and chemical energy. Most forms of energy can also be classified as kinetic or potential energy. Kinetic and potential forms of mechanical energy are the focus of this lesson. Mechanical energy is the energy of an object that is moving or has the potential to move. It is the sum of an object’s kinetic and potential energy. In Figure below, the basketball has mechanical energy because it is moving. The arrow in the same figure has mechanical energy because it has the potential to move due to the elasticity of the bow. What are some other examples of mechanical energy? Kinetic and potential energy add up to mechanical energy. Station 2: Kinetic Energy Moving things have kinetic energy. The heavier a thing is and the faster it moves the more kinetic energy it has. All moving things have kinetic energy, even very large things, like planets, and very small ones, like atoms. What do all the photos in Figure below have in common? All of them show things that are moving. Kinetic energy is the energy of moving matter. Anything that is moving has kinetic energy—from the atoms in matter to the planets in solar systems. Things with kinetic energy can do work. For example, the hammer in the photo is doing the work of pounding the nail into the board. You can see a cartoon introduction to kinetic energy and its relation to work at this URL:http://www.youtube.com/watch?v=zhX01toLjZs. All of these photos show things that have kinetic energy because they are moving. The amount of kinetic energy in a moving object depends on its mass and velocity. An object with greater mass or greater velocity has more kinetic energy. The kinetic energy of a moving object can be calculated with the equation: This equation for kinetic energy shows that velocity affects kinetic energy more than mass does. For example, if mass doubles, kinetic energy also doubles. But if velocity doubles, kinetic energy increases by a factor of four. That’s because velocity is squared in the equation. You can see for yourself how mass and velocity affect kinetic energy by working through the problems below. Problem Solving Problem: Juan has a mass of 50 kg. If he is running at a velocity of 2 m/s, how much kinetic energy does he have? Solution: Use the formula: You Try It! Problem: What is Juan’s kinetic energy if he runs at a velocity of 4 m/s? Problem: Juan’s dad has a mass of 100 kg. How much kinetic energy does he have if he runs at a velocity of 2 m/s? Station 3: Potential Energy Did you ever see a scene like the one in Figure below? In many parts of the world, trees lose their leaves in autumn. The leaves turn color and then fall from the trees to the ground. As the leaves are falling, they have kinetic energy. While they are still attached to the trees they also have energy, but it’s not because of motion. Instead, they have stored energy, called potential energy. An object has potential energy because of its position or shape. For example leaves on trees have potential energy because they could fall due to the pull of gravity. Before leaves fall from trees in autumn, they have potential energy. Why do they have the potential to fall? Gravitational Potential Energy Potential energy due to the position of an object above Earth is called gravitational potential energy. Like the leaves on trees, anything that is raised up above Earth’s surface has the potential to fall because of gravity. You can see examples of people with gravitational potential energy in Figure below. At the URL below, you can watch a cartoon introduction to gravitational potential energy. Elastic Potential Energy Potential energy due to an object’s shape is called elastic potential energy. This energy results when elastic objects are stretched or compressed. Their elasticity gives them the potential to return to their original shape. For example, the rubber band in Figure below has been stretched, but it will spring back to its original shape when released. Springs like the handspring in the figure have elastic potential energy when they are compressed. What will happen when the handspring is released? A) C) B) D) E) Station 4: Sound energy A vibrating drum and a plucked guitar string transfer energy to the air as sound. Kinetic energy from the moving air molecules transfers the sound energy to your eardrum. The drummer in Figure below is hitting the drumheads with drumsticks. This causes the drumheads to vibrate. The vibrations pass to surrounding air particles and then from one air particle to another in a wave of energy called sound energy. We hear sound when the sound waves reach our ears. Sound energy can travel through air, water, and other substances, but not through empty space. That’s because the energy needs particles of matter to pass it on. Vibrating objects such as drumheads produce sound energy. If an object is vibrating quickly, it has a higher frequency and shorter wavelength. As a result, the sound is more high-pitched. On the other hand (or claw), if it is vibrating more slowly, the wave has a lower frequency and longer wavelength, emitting a more low-pitched sound. This quality is measured in units of Hertz, with more Hertz indicating higher pitches. If the sound wave is larger in height, it has greater amplitude and therefore a louder sound. If the sound wave is smaller in height, it has lower amplitude and a quieter sound. Station 5: Thermal energy Thermal energy is what we call energy that comes from heat. A cup of hot tea has thermal 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. The atoms that make up matter are in constant motion, so they have kinetic energy. All that motion gives matter thermal energy. Thermal energy is defined as the total kinetic energy of all the atoms that make up an object. It depends on how fast the atoms are moving and how many atoms the object has. Therefore, an object with more mass has greater thermal energy than an object with less mass, even if their individual atoms are moving at the same speed. You can see an example of this inFigure below. Atoms are moving at the same speed in the pasta on the fork as they are in the pasta on the plate. However, there are more atoms of pasta on the plate, so it has more thermal energy. Heat and temperature are not the same thing, although both are concerned with thermal energy. The heat an object contains is the amount of its thermal energy, measured in joules or J. 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 °C, (not °c or oC). A thermometer is used to measure the temperature of an object Let's look at two examples to see the difference between heat and temperature. Example 1 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 than the cup of tea. Example 2 To boil water we must increase its temperature to 100°C. It takes longer to boil a large beaker of water than a small beaker because the large beaker contains more water and needs more thermal energy to reach 100°C. Thermal energy can be transferred in three different ways: conduction, convection, and radiation. Station 6: Conduction (Thermal Energy Transfer) Thermal energy can be transferred by the process of CONDUCTION. 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. Stages in conduction This is how the handle of a metal spoon soon gets hot when the spoon is put into a hot drink. 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. Station 7: Convection (Thermal Energy Transfer) Thermal energy can be transferred by 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. Station 8: Radiation (Thermal Energy Transfer) All objects transfer thermal energy by infrared radiation. The hotter an object is, the more infrared 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 how we can feel the heat of the Sun, even though it is millions of kilometres away in space. Infrared cameras give images even in the dark, because they are detecting heat, not visible light. Conduction and convection need moving particles to transfer the thermal energy, but radiation does not. Station 9: Chemical energy Chemical energy is stored in wood and released when the wood burns. Some chemical reactions release energy. For example, when an explosive goes off, chemical energy stored in it is transferred to the surroundings as thermal energy, sound energy and kinetic energy. Energy is stored in the bonds between atoms that make up compounds. This energy is called chemical energy, and it is a form of potential energy. If the bonds between atoms are broken, the energy is released and can do work. The wood in the fireplace in Figure below has chemical energy. The energy is released as thermal energy when the wood burns. People and many other living things meet their energy needs with chemical energy stored in food. When food molecules are broken down, the energy is released and may be used to do work. Station 10: Electrical energy Electrons are negatively charged particles in atoms. Moving electrons have a form of kinetic energy called electrical energy. If you’ve ever experienced an electric outage, then you know how hard it is to get by without electrical energy. Most of the electrical energy we use is produced by power plants and arrives in our homes through wires. Two other sources of electrical energy are pictured in Figure below. A lightning bolt is a powerful discharge of electrical energy. A battery contains stored chemical energy and converts it to electrical energy. Bulb and battery A battery transfers stored chemical energy as electrical energy in moving charges in wires. For example, electrical energy is transferred to the surroundings by the lamp as light energy and thermal energy. Station 11: Nuclear Energy The nuclei of atoms are held together by powerful forces. This gives them a tremendous amount of stored energy, called nuclear energy. The energy can be released and used to do work. This happens in nuclear power plants when nuclei fission, or split apart. It also happens in the sun and other stars when nuclei fuse, or join together. Some of the sun’s energy travels to Earth, where it warms the planet and provides the energy for photosynthesis (see Figure below). In the sun, hydrogen nuclei fuse to form helium nuclei. This releases a huge amount of energy, some of which reaches Earth. Station 12: 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 to the left. 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: Station 13: 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. This Sankey diagram for the lamp 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. Station 14: Electromagnetic Energy Energy that the sun and other stars release into space is called electromagnetic energy. This form of energy travels through space as electrical and magnetic waves. Electromagnetic energy is commonly called light. It includes visible light, as well as radio waves, microwaves, and X rays (Figure below). Radio waves, microwaves, and X rays are examples of electromagnetic energy. Station 15: Non-renewable Sources of Energy: FOSSIL FUELS We get energy from many different types of energy resources, including fuels, 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. On the this page we'll look at non-renewable resources. Fossil fuels Coal, oil and natural gas are called fossil fuels. They formed millions of years ago from the remains of living things. Coal was formed from plants. Oil and natural gas were formed from sea creatures. 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 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. 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. Once we have used them all up, they will take millions of years to replace, if they can be replaced at all. For this reason we call fossil fuels non-renewable energy resources. 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. 1. the fuel is burned to boil water to make steam 2. the steam makes a turbine spin 3. the spinning turbine turns a generator which produces electricity 4. the electricity goes to the transformers to produce the correct voltage As the fossil fuels are non-renewable energy resources, and they also produce pollution when they burn, we are aiming to produce more of our electricity using other, renewable energy resources. This will reduce the rate at which the fossil fuels are used up. Reducing energy use We can also reduce the rate at which the fossil fuels are used up by saving energy. For example, we can: walk to instead of getting using cars where possible turn down the heating turn off the lights when leaving the room Station 16: Renewable Resources Renewable energy resources can be replaced, and will not run out. Be careful - it is not true to say that they can be re-used. 1) BIOMASS Biomass fuels come from living things. 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 came originally from the Sun. 2) WIND 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 so high it would damage them. 3) WATER 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 gravitational potential energy which is released when it falls. As the water rushes down through pipes, this stored energy is transferred to kinetic energy, which turns electricity generators. An energy transfer diagram for an HEP scheme: 4) GEOTHERMAL In some places the rocks underground are hot. Deep wells can be drilled and cold water pumped down. The water runs through fractures in the rocks and is heated up. It returns to the surface as hot water and steam, where its energy can be used to drive turbines and electricity generators 5) SOLAR POWER Solar cells are devices that convert light energy directly into electrical energy. You may have seen small solar cells on calculators. Larger arrays of solar cells are used to power road signs, and even larger arrays are used to power satellites in orbit around Earth. Solar panels are different to solar cells. Solar panels do not generate electricity. Instead they heat up water directly. A pump pushes cold water from a storage tank through pipes in the solar panel. The water is heated by heat energy from the Sun and returns to the tank. They are often located on the roofs of buildings where they can receive the most sunlight. Generating electricity 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.