LECTURE NOTES - AOS 132 Lecture 2/6/08 *Correction from...

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AOS 132 Lecture 2/6/08 *Correction from last lecture: Mass/Volume should be < (less than) density of water for boats to float Energy Units – Joule, KWatt/hr, BTU Classification – 2 general categories Realized (happening right now, recognizable, hard to store); forms include… 1. Kinetic – motion of a body, (e.g. water flowing through hydroelectric generator) 2. Thermal or heat – proportional to temperature of the body; heat capacity for liquid water is 4.2 Joules/(gram x ˚ C), ice is 2.1 J/(g x ˚C); energy moves from higher to lower temperature 3. Electrical – flow of electrons through a conductor Potential (energy is present but hidden, becomes useful if certain conditions are met) 1. Gravitational – energy by virtue of distance from Earth’s surface (e.g. a ball tossed way in the air has gravitational potential energy); in hydroelectric generation, water is held behind dam with potential, then released through a generator energy 2. Chemical – held in chemical bonds, released or absorbed by chemical reactions (e.g. batteries); phase changes are another example where energy is either released or absorbed when water changes states Energy Transfer Mechanisms Collision – something with kinetic energy hits something else and transfers it Conduction – movement of thermal/heat energy through a solid or still fluid Electromagnetic radiation – invisible energy transfer from warmer to cooler bodies by radiation (e.g. this is how the sun warms the earth; giving off body heat) Convection – movement of energy in a moving fluid (e.g. Gulfstream –“Learn@UW, Content, Gulfstream” for picture) Phase Change Solid-----> melting ----->Liquid-----> evaporating ----->Gas (vapor) Gas-----> condensing ----->Liquid-----> freezing-----> Solid To change from the solid phase to liquid or vice versa requires 354 J/g of energy transfer (heat of fusion) To change from a liquid to gas (vapor) or vice versa requires 2450 J/g of energy transfer These two numbers are referred to as Latent heats Sedentary human – daily metabolic energy 8.4 mega Joules (MJ), how much is burned up; by latent heat values, this is enough energy to evaporate about 3.4 L of water Phase Transition Temperatures Solid to liquid = O˚C, 32˚F Liquid to gas = 100˚C, 212˚F (boiling point – when water vapor bubbles form in liquid) At transition temperature, system stays at that temperature until phase change is complete (e.g. full glass of ice and water stays at 0˚C until all ice is melted) Phase transition temperatures are affected by elevation Vapor Phase
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If the water is covered (such as by a plate) are will have a concentration of water vapor that stays steady; an equal number of water molecules jumps from the water to the air and back to the water This is called “saturation vapor concentration” If it is uncovered, water molecules will move in and out but some will escape, and slowly it will run out (evaporation)
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This note was uploaded on 04/07/2008 for the course AOS 132 taught by Professor Martin during the Spring '08 term at Wisconsin.

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LECTURE NOTES - AOS 132 Lecture 2/6/08 *Correction from...

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