Energy, Temperature, & Heat Energy is the ability to do work (push, pull, lift) on some form of matter. Chapter 2 Potential energy is the potential for work (mass x gravity x height) Kinetic energy is energy of a moving object (half of mass x velocity squared) Temperature is the average speed of atoms and molecules 1 2 Energy, Temperature, & Heat Which has more energy? A lake or a cup of hot tea? Heat is the energy in the process of being transferred from one object to another because of a difference in temperature. Energy cannot be destroyed or created; First Law of Thermodynamics Fig. 2-1, p. 331 4 Temperature Scales Fahrenheit: 32 freeze, 212 boil Celsius: 0 freeze, 100 boil Kelvin: absolute; 0K = -273 C 5 6 1
Specific Heat Heat capacity is the heat energy absorbed to raise a substance to a given temperature Specific heat is the heat capacity divided by mass or the amount of energy required to raise one gram of a substance 1 C High specific heat equates to slow warming and vice versa 7 Table 2-1, p. 832 Latent Heat Change of state or phase change represents change between solid, gas, and liquid. Latent heat is the energy involved in the change of state. What does latent mean? Ice to vapor: absorb energy, cool environment (melt, evaporation, sublimation) Vapor to ice: release energy, heat environment (freeze, condense, deposition) 9 Fig. 2-3, p. 1033 Heat Transfer in the Atmosphere Conduction: transfer heat from one molecule to another in a substance Energy travels from hot to cold Air a poor conductor, metal a good conductor 11 12 2
Heat Transfer in the Atmosphere Convection: transfer of heat by the mass movement of a fluid (water or air) Convection circulation: warm air expands and rises then cools and sinks; thermal cell Table 2-2, p. 1334 14 Heat Transfer in the Atmosphere Special Topic: Rising and Sinking As air rises part of it s energy is lost as it expands and cools and when the air sinks it is compressed and the energy of molecules increase causing temperature to increase. 15 16 Radiation Energy from the sun travels through the space and the atmosphere in the form of a wave (electromagnetic waves) and is called radiation. Radiation and Temperature All objects with a temperature greater than 0K radiate energy. As temperature of an object increases, the more total radiation that is emitted by an object Fig. 2, p. 1736 Stefan Boltzmann Law: E = σt 4 18 3
19 20 Radiation Radiation of the Sun and Earth Sun 6000k emits radiation, electromagnetic spectrum Shortwave radiation (high energy) from the Sun Longwave radiation (low energy) from the Earth 21 Fig. 2-9, p. 2239 Radiation Environmental Issue: Sunburn UV index is a weather forecast product that indicates the potential for sun burn due to high energy or short wavelengths emitted by the sun. http://www.epa.gov/sunwise/uvindex.html Fig. 2-10, p. 2339 24 4
Balancing Act Selective Absorbers If the Earth is radiating energy all the time, why is it not very cold? Radiative equilibrium Absorb > emit = warm Emit > absorb = cool Good absorbers are good emitters at a particular wavelength and vice versa. Greenhouse effect: the atmosphere selectively absorbs infrared radiation from the Earth s surface but acts as a window and transmits shortwave radiation 25 26 Fig. 2-11, p. 2742 28 Greenhouse Enhancement Incoming Solar Radiation Global warming is occurring due to an increase in greenhouse gases Carbon dioxide Methane Nitrogen Oxide Chlorofluorocarbons Greenhouse Effect vs. Atmospheric Greenhouse Effect Positive feedbacks continue the warming trend. Negative feedbacks decrease warming. 29 Conduction, convection, and infrared radiation warm the atmosphere from below, not sunlight or insolation from above. Scattering Reflection, albedo 30 5
1/17/11 Table 2-3, p.3148 Fig. 2-12, p.3243 Fig. 2-17, p. 49 Fig. 2-18, p.3649 The Energy Balance On an overall annual average for the whole planet, Earth and atmosphere absorb energy from the sun and each other. A balance is maintained so the planet s average temperature remains constant year-to-year. The planet absorbs 70% of the sun s radiant energy and reflects the same amount into space. Stepped Art 33 Fig. 2-17, p.3549 34 6
Incoming Solar Radiation Observation: Blue skies, red skies, and white clouds Selective scattering of incoming solar radiation causes reflectance in portion of the electromagnetic spectrum that correspond with the colors our eyes detect. 37 38 39 40 Particles and Aurora Solar wind or plasma is charged traveling through space from sun to Earth. Solar wind interacts with Earth s magnetosphere and creates auroras Aurora borealis Aurora australis 41 42 7
43 44 45 46 Homework for Chapter 2 Chapter 2 Questions for Review, p. 53 #1-3, 5, 7, 9-14, 16, 21 Chapter 2 Problems and Exercises, p. 54 #1 47 48 8
Project for Chapter 2 None 49 9