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4 Energy and Heat Transfer

4 Energy and Heat Transfer - Energy and Heat Transfer...

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Unformatted text preview: Energy and Heat Transfer GEOG345 Sep 12 2006 Textbook: chapter 2 (1 st half) Energy • energy – energēs (Greek): at work • energy is the ability or capacity to do work on some form of matter • various forms exist – mechanical energy – position and movement of objects – radiant energy • it can change from one form to another • total amount of energy in a closed system remains constant – law of conservation of energy – first law or thermodynamics Mechanical energy • gravitational potential energy (PE) PE=m∙g∙h – m: mass of the object – g: acceleration of gravity – h: height above ground • kinetic energy (KE) KE=½∙m∙v 2 – m: mass of the object – v: velocity • SI unit of energy: Joule (J) 1 J=1 N∙m=1 kg∙m 2 /s 2 Temperature, internal energy and heat • air (atoms and) molecules have kinetic energy due to their motion • temperature is a measure of the average kinetic energy • internal energy is the total energy (potential and kinetic) stored by the molecules • heat is energy in the process of being transferred due to temperature difference (or temperature gradient ) Fig. 2-1, p. 29 Temperature and density Temperature scales • absolute zero: no thermal motion • Kelvin scale (K) – starts at the absolute zero • Celsius scale (˚C) – same units as the Kelvin scale – 0˚C: freezing temperature of pure water – 100˚C: boiling temperature of water at sea level • Fahrenheit scale (˚F) – freezing temperature of pure water: 32˚F – boiling temperature of water at sea level: 212˚F Temperature conversions K= ˚C + 273.15 ˚C = 5/9 (˚F-32) ˚F = 9/5 (˚C+32) K = 5/9 (˚F-32) + 273.15 Fig. 2-2, p. 30Fig....
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4 Energy and Heat Transfer - Energy and Heat Transfer...

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