Transcript Energy
Chapter 15 Energy 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy and Work Work is done when a force moves an object through a distance. Energy is the ability to do work. Energy is transferred by a force moving an object through a distance. 15.1 Energy and its Forms Energy Work and energy are closely related. When work is done on an object, energy is transferred to that object. Work is a transfer of energy. 15.1 Energy and its Forms Energy Both work and energy are measured in joules. The work done when an object is moved 1 meter by a 1-newton force equals 1 joule. Although energy can take many forms, it can always be measured in joules. 15.1 Energy and its Forms Energy Many forms of energy can be classified into two general types: • kinetic energy • potential energy 15.1 Energy and its Forms Energy Kinetic Energy The energy of motion is called kinetic energy. (Greek kinetos means moving). The kinetic energy of any moving object depends upon its mass and speed. KE=½mv2 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy Potential Energy Potential energy is energy stored as a result of position, (condition), or shape. Two forms of potential energy are • gravitational potential energy • elastic potential energy 15.1 Energy and its Forms Energy Gravitational Potential Energy Potential energy that depends upon an object’s height is called gravitational potential energy (PEg). This type of energy increases when an object is raised to a higher level. 15.1 Energy and its Forms Energy An object’s PEg depends on its mass (in kg), its height (in m), and the acceleration due to gravity (9.8 m/s2 near Earth’s surface). PEg=mgh Gravitational potential energy is measured relative to some reference level. 15.1 Energy and its Forms Energy Elastic Potential Energy The potential energy of an object that is stretched or compressed is known as elastic potential energy (PEelastic). An object is said to be elastic if it springs back to its original shape after it is stretched or compressed. PEelast=½kx2. 15.1 Energy and its Forms Energy k is defined as spring constant and depends on type of spring material x is defined as distance stretched or compressed 15.1 Energy and its Forms Energy Forms of Energy All energy can be considered to be kinetic energy, potential energy, or the energy in fields such as those produced by electromagnetic waves. 15.1 Energy and its Forms Energy The major forms of energy are • mechanical energy • thermal energy • chemical energy • electromagnetic energy • nuclear energy Each of these can be converted into other forms of energy. 15.1 Energy and its Forms Energy Mechanical Energy The energy associated with the motion and position of objects is mechanical energy. Mechanical energy is the sum of an object’s PE and KE. 15.1 Energy and its Forms Energy Mechanical energy does not include thermal energy, chemical energy or other forms of energy associated with the motion or the arrangement of atoms or molecules. 15.1 Energy and its Forms Energy Thermal Energy The total potential and kinetic energy of all the microscopic particles in the object make up its thermal energy. 15.1 Energy and its Forms Energy Chemical Energy Chemical energy is the energy stored in chemical bonds. When bonds are broken, the energy is released. 15.1 Energy and its Forms Energy Electric Energy Electric energy is the energy associated with electric charges. Batteries convert chemical energy to electric energy. Electric energy also occurs in nature in the form of lightning. 15.1 Energy and its Forms Energy Electromagnetic Energy Electromagnetic energy is a form of energy that travels through space in the form of waves. Travel at 15.1 Energy and its Forms Energy 15.1 Energy and its Forms Energy Nuclear Energy The nucleus of an atom is held together by strong and weak nuclear forces, which store tremendous amounts of potential energy known as nuclear energy. 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy Conversion Energy can be converted from one form to another in a process known as energy conversion. For example light bulbs convert electric energy into thermal energy and electromagnetic energy. 15.2 Energy Conversion and Conservation Energy Conservation of Energy When energy changes from one form to another, the total energy remains unchanged even though many conversions may occur. The law of conservation of energy states that energy cannot be created or destroyed. 15.2 Energy Conversion and Conservation Energy In a closed system, the amount of energy present at the beginning of a process is the same as the amount of energy at the end. 15.2 Energy Conversion and Conservation Energy How Can Energy Change Forms? Rube Goldberg was an award-winning cartoonist who drew complex series of devices that performed relatively simple acts. The devices were arranged so that the output of one device would act as the input of the next. 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy 1. List at least three kinds of energy in the device. 2. Describe one change, in which energy from one form is converted into energy of another form. 15.2 Energy Conversion and Conservation Energy Energy Conversions One of the most common energy conversions is between potential energy and kinetic energy. The PEg of an object is converted to KE as the object falls. Conversions between KE and PEg can happen in both directions. 15.2 Energy Conversion and Conservation Energy Energy Conversion in Pendula A pendulum consists of a weight swinging back or forth from an arm. Pendulum clocks make use of the fact that the time it takes for a pendulum to swing back and forth is precisely related to its length. KE and PE undergo constant conversion as a pendulum swings. 15.2 Energy Conversion and Conservation Energy At the highest point in its swing, the pendulum is momentarily motionless as it changes direction. At this point, the bob has KE=0 and PEg is at its maximum. 15.2 Energy Conversion and Conservation Energy As the pendulum swings downward, the PEg is converted to KE. At the bottom of the swing, KE is at its maximum and PEg=0. The pendulum continues upward and the process repeats. 15.2 Energy Conversion and Conservation Energy The period of a pendulum is the time to it takes to make one complete swing and return to its starting position. The period (T) depends only on the length (l) of the pendulum arm T 2 l g 15.2 Energy Conversion and Conservation Energy Energy Conversion Calculations When friction is small enough to be ignored, and no mechanical energy is added to a system, the mechanical energy does not change. MEi=(KEi + Pei) = (KEf + PEf ) = MEf 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy 15.2 Energy Conversion and Conservation Energy Energy and Mass Einstein’s equation, E=mc2, says that energy and mass are equivalent and can be converted into each other. The law of conservation of energy has been modified to say that mass and energy are always conserved. 15.3 Energy Resources Energy 15.3 Energy Resources Nonrenewable Energy Resources Nonrenewable energy resources exist in limited quantities and, once used, cannot be replaced except over millions of years. Nonrenewable resources include fossil fuels and uranium. 15.3 Energy Resources Energy Renewable Energy Resources Renewable energy resources are those that can be replaced in a relatively short period of time (one life span). Most renewable energy resources originate either directly or indirectly from the sun. 15.3 Energy Resources Energy Renewable energy resources include • hydroelectric • solar • geothermal • wind • biomass 15.3 Energy Resources Energy 15.3 Energy Resources Energy Hydroelectric Energy Energy obtained from flowing water is known as hydroelectric energy. As the water flows downhill, its PEg is converted into KE. This kinetic energy can be used to turn turbines that are connected to electric generators. 15.3 Energy Resources Energy 15.3 Energy Resources Energy 15.3 Energy Resources Energy Solar Energy Sunlight that is converted into usable energy is called solar energy. Passive solar designs use sunlight to heat a building without using machinery. 15.3 Energy Resources Energy 15.3 Energy Resources Energy In an active solar energy system, sunlight heats collection plates through which water flows. Sunlight can also be converted directly into electrical energy by means of solar cells, or photovoltaic cells. The benefits of solar energy depend on the climate. 15.3 Energy Resources Energy 15.3 Energy Resources Energy 15.3 Energy Resources Energy Geothermal Energy Geothermal energy is thermal energy beneath Earth’s surface. It is nonpolluting but not widely available. 15.3 Energy Resources Energy 15.3 Energy Resources Energy Other Renewable Resources The chemical energy stored in living things is called biomass energy. A hydrogen fuel cell generates electricity by reacting hydrogen and oxygen. 15.3 Energy Resources Energy Conserving Energy Resources 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.