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HIGH SCHOOL SCIENCE Physical Science 5: Energy WILLMAR PUBLIC SCHOOL 2013-2014 EDITION C HAPTER 5 Energy In this chapter you will: 1. Describe the relationship between work and energy 2. Relate kinetic energy to mass and speed 3. Analyze how potential energy is related to an object’s position 4. Define gravitational potential energy and elastic potential energy 5. Describe the major forms of energy 6. Describe the law of conservation of energy 7. Classify renewable and nonrenewable energy resources S ECTION 5.1 Imagine you have been swimming for a long time. You are tired. Some friends ask you to play volleyball, but you say that you do not have the energy. What exactly do you mean? What is energy? Energy Energy is the ability to do work. In other words, energy is transferred by a force moving an object through a distance. When you hit a volleyball, you move it. When you jump and run, you move yourself. Playing volleyball, jumping and running all take energy. Sound and motion are examples of energy in action. O BJECTIVES : 1. Describe the relationship between work and energy. 2. Relate kinetic energy to mass and speed. 3. Analyze how potential energy is related to an object’s position. 4. Define gravitational potential energy and elastic potential energy. Vocabulary: energy work joule kinetic energy potential energy elastic potential energy gravitational potential energy Work and energy are closely related. Work is a transfer of energy. When work is done on an object, energy is transferred to that object. Both work and energy are typically measured in joules (J). Recall that 1 joule equals 1 newton-meter, the work done when an object is moved 1 meter by a 1-newton force. Although energy can take many different forms, it can always be measured in joules. All energy can be considered to be kinetic energy, potential energy, or the energy in fields such as those produced by electromagnetic waves. Many forms of energy can be classified into two general types: kinetic energy and potential energy. The energy of motion is called kinetic energy. The kinetic energy of any moving object depends upon its mass and speed. To calculate the kinetic energy of an object in joules, 2 multiply ½ by the object's mass (m) in kilograms and the square of its speed (v) in meters per second. Kinetic Energy = 1/2 mv2 Potential energy is energy that is stored as a result of position or shape. Plucking a string and lifting a book are two examples of stored energy—energy with the potential to do work. Two forms of potential energy are gravitational potential energy and elastic potential energy. Potential energy that depends upon an object's height is called gravitational potential energy. This type of potential energy increases when an object is raised to a higher level. An object's gravitational potential energy depends on its mass (m), its height (h), and the acceleration due to gravity (g). The potential energy of an object that is stretched or compressed is known as elastic potential energy. Potential Energy = mgh Section Review: 1. How are energy and work related? 2.What unit used to measure work and/or energy? 3. What can all energies be considered? 4.What does kinetic energy depend on? 5. What is the equation for kinetic energy? 6.What are some examples of potential energy? 7. What are the two forms of potential energy? 8.What does gravitational potential energy depend on? 9.How is mechanical energy related to potential energy and kinetic energy? 10.Can an abject have both kinetic energy and potential energy at the same time? Explain. Objects can have both potential energy and kinetic energy. The total amount of potential energy and kinetic energy that an object has is called mechanical energy. Energy is not matter, because it does not have mass or take up space. You cannot see energy, but you can see what energy does. Each kind of energy can change into other kinds of energy. 3 S ECTION 5.2 Energy & Its Forms O BJECTIVES : 1. Describe the major forms of energy. Vocabulary: mechanical energy thermal energy conduction convection radiation chemical energy electric energy electromagnetic energy nuclear energy The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy, and nuclear energy. Each of these forms of energy can be converted into other forms of energy. The energy associated with the motion and position of everyday objects is mechanical energy. Mechanical energy is the energy associated with the motion and position of everyday objects and the sum of an objects potential energy and kinetic energy. A roller coaster has potential energy at the top of each hill. Each time that roller coaster moves downhill, it has kinetic energy. As it moves down the hill it has both kinetic energy, since it is moving, and potential energy, since it has the potential to keep moving> The coaster’s energy keeps changing from kinetic to potential, but the total mechanical energy stays the same. The total potential and kinetic energy of all the microscopic particles or atoms in an object make up its thermal energy. Tiny particles, or molecules, that make up matter are always moving the energy created by their movement is called thermal energy. Thermal energy is the energy of heat. When an object's atoms move faster, its thermal energy increases and the object becomes warmer. Thermal energy passes hear from one object to anther. Thermal energy can be passed from one object to another. Heat always passes from a hotter object to a cooler object. The heat energy makes the molecules in the cooler object more faster. Heat can be passed three ways: conduction, convection, and radiation. Heat passes through solids by conduction. When one object 4 passes to another by conduction, the heat keeps flowing until both objects are equally hot. Convection is the way heat passes through liquids and gases. Molecules in liquids and gases move apart when they are heated. Radiation moves in waves. Solar heat comes to you in radiation or electromagnetic energy. Chemical energy is the energy stored in chemical bonds. When bonds are broken, the released energy can do work. When there is a chemical reaction, the bonds break and chemical energy is released. All chemical compounds, including fuels such as coal and gasoline, store energy. Gasoline has chemical energy. When gasoline is burned in a car’s engine, the chemical energy is changed to mechanical energy. The mechanical energy moves the car. Wood released stored chemical energy when it is burned. energy that travels through space in the form of waves. Radiation is electromagnetic energy. Electromagnetic energy can move through empty space. All the energy in the world comes from the sun. The sun’s energy is called solar energy. Solar energy is a type of electromagnetic energy On Earth, solar energy is changed to other kinds of energy. Nothing on Earth could live without energy from the sun. The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy. The energy stored in atomic nuclei is known as nuclear energy. Nuclear energy is given off when the nucleus breaks apart or fuses with the nucleus of another atom. Nuclear energy is produced in nuclear power plants. Many devices you use every day use electricity, or electrical energy. The particles in matter have positive and negative charges. Electrons are the negatively charged particles. The movement of electrons produces electrical energy. Electrical energy is the energy associated with electric charges. Electric charges can exert forces that do work. The wires in home carry electrical energy. Electrical energy makes light bulbs light up and radios play. Lightning is a form of electrical energy. The sun radiates electromagnetic energy into space and is the source, either directly or indirectly, of most of the world's energy supplies. Electromagnetic energy is a form of 5 Section Review: 1. When you heat a pot of water over a flame, what form of energy is added to the water? 2.Give an example of each form of energy. 3. When you eat food, which form of energy are you getting? 4.Which form of energy travels through space in the form of waves? 5. Which form of energy increases as atoms within an object move faster? 6 S ECTION 5.3 Converting Energy Energy cannot be created or destroyed, but it can be converted from one form to another. The process of changing energy from one form to another is energy conversion. Energy conversions are constantly taking place all around you, often without you noticing. Energy from the sun, or solar energy, travels as light, or electromagnetic energy, to Earth. Green plants trap light energy and change it into chemical energy. When an animal eats the plants, the chemical energy is released. When energy changes from one form to another, the total energy remains unchanged even though many energy conversions may occur. This is one of the most important concepts in science, the law of conservation of energy. The law of conservation of energy states that energy cannot be created or destroyed. According to the law of conservation of energy, energy can be converted from one form to another. O BJECTIVES : 1. Describe the law of conservation of energy. Vocabulary: energy conversion law of conservation of energy One of the most common energy conversions is between potential energy and kinetic energy. The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls. Physicist Albert Einstein (1879–1955) developed his special theory of relativity in 1905. This theory included the nowfamous equation E = mc2. In Einstein's equation, E is energy, m is mass, and c is the speed of light. E = mc2 says that energy and mass are equivalent and can be converted into each other. In other words, energy is released as matter is destroyed, and matter can be created from energy. 7 Section Review: 1. What happens to the total amount of energy as it changes from one form to another? 2.What is the law of conservation of energy? 3. What is the most common energy conservation? 4.What does E = mc2 say about energy and mass? 5. In the equation E = mc2, what does the c represent? 6.What happens when matter is destroyed? 7. Can matter be created from energy? 8 S ECTION 4 Conserving Energy O BJECTIVES : 1. Classify renewable and nonrenewable energy resources. Vocabulary: nonrenewable energy fossil fuels nuclear fission nuclear fusion renewable energy hydroelectric energy turbine generator solar energy geothermal wind energy Most of Earth’s resources are used as energy resources. Energy is used for transportation, manufacturing, and countless other things that are important to life as we know it. Energy resources can be classified as either nonrenewable or renewable. Nonrenewable energy resources exist in limited quantities and, once used, cannot be replaced except over the course of millions of years. Nonrenewable energy resources include oil, natural gas, coal, and nuclear energy. Such resources are currently being used much faster than they can be replaced, creating concern about how long they will last. Some of the most important nonrenewable resources are buried within the Earth’s curst and are know as fossil fuels. Oil, natural gas, and coal are known as fossil fuels because they were formed underground from the remains of onceliving organisms. Fossil fuels consist primarily of compounds of carbon and hydrogen. These compounds contain stored energy originally obtained from the sunlight by plants and animals that lived millions of year ago. Currently, fossil fuels account for the great majority of the world's energy use. Energy that is produced by bombarding atomic nuclei with high energy particles is called nuclear energy. One form of nuclear energy is produced by splitting the nuclei of heavy atoms, like uranium, is called nuclear fission. Nuclear power plants use nuclear fission and burn not fossil fuels or produce no air pollution. However, nuclear fission produces 9 radioactive materials. Radiation an make people very sick. All of the energy that reaches Earth from the sun is produced by nuclear fusion. During nuclear fusion, the nuclei of hydrogen atoms combine to form larger nuclei of helium and releases energy. Renewable energy resources are resources that can be replaced in a relatively short period of time. Most renewable energy resources originate either directly or indirectly from the sun. The sun and Earth are constantly releasing large amounts of energy. This energy could be used for generating electric power, heating buildings, or other purposes. Renewable energy resources include hydroelectric, solar, geothermal, wind, biomass, and, possibly in the future, nuclear fusion. The challenge for engineers and scientists is to find efficient ways to make these energy resources inexpensive and convenient. One of the oldest sources of energy comes from moving water. Hydroelectric energy is energy obtained from flowing water. As water flows downhill, its gravitational potential energy is converted into kinetic energy. This kinetic energy can be used to turn turbines that are connected to electric generators. A turbine is like a waterwheel, but turns very fast. A generator makes electricity. Most hydroelectric power plants rely on natural flow of water in a river. But most modern power plants rely on dams across rivers. The major advantages of hydroelectric energy include its low cost to produce and lack of pollution; however, dams cause a variety of environmental problems. Another source of renewable energy is the sun. Solar energy is the sun’s energy converted into usable energy. Solar energy can be collected by passive systems or active systems. The benefits of solar energy depends on the climate. Solar energy is nonpolluting, but for areas where cloudy days are frequent, solar energy is less practical. Geothermal is the heat from beneath Earth’s surface. Water is pumped into the ground, where it turns into steam then drives a generator. Geothermal energy is nonpolluting, but is not widely available. Wind is the movement of air over Earth’s surface. Wind results from air pressure differences caused by the sun’s uneven heating of the Earth’s surface. Wind energy is energy obtained from the movement of wind. Wind turbines converts the kinetic energy into electric energy using the turbine and generator. Wind energy does not pollute; however, area with little wind cannot benefit from it. Fossil fuel supplies may become increasingly scarce and expensive in the future. An important way to make these energy resources last longer is to use them more slowly. Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use. Finding ways to use less energy or to use energy more efficiently is known as energy conservation. 10 People can reduce the use of these resources by making energy-saving decisions, for example turning off lights when they are not being used. Because cars consume an enormous amount of energy, the decisions that people make about transportation are very important. Walking or biking on short trips and carpooling can save considerable energy. Making appliances, cars, and even light bulbs more energy efficient is a way of reducing energy use while still enjoying its benefits. Much has already been done to make appliances more energy efficient. Light bulbs have been developed that provide superior lighting at a lower energy cost. The technology for further improvement, including more fuelefficient cars, is already known in many cases. Section Review: 1. What resources are considered nonrenewable? 2.What is the concern about nonrenewable resources? 3. What are fossil fuels? 4.What resources are considered renewable? 5. Which energy resource would be best used in the dessert? Why? 6.How can you conserve energy? 11