Lecture 3 intermLecture3forPosting

Lecture 3 intermLecture3forPosting - Physics 7A -- Lecture...

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Unformatted text preview: Physics 7A -- Lecture 3 Winter 2010 Prof. Robin D. Erbacher 343 Phy/Geo Bldg erbacher@physics.ucdavis.edu E thermal E bond E movement (KE) E gravity E electric E spring ........ Energy is converted from one form to another, but never created or destroyed! Steam engine Nuclear power plant There are many different forms of energy ( energy systems) : E thermal = C T = mc T, Temperature is the indicator. Between phase changes, only thermal energy changes. E bond = | m H| , m is the indicator. At a physical phase change, only the bond-energy system changes. H is the heat of the particular phase change. m is the amount that changed phase. In a chemical reaction, there are several bond energy changes corresponding to diff. molecular species (reactants or products). Here H is the heat of formation for a particular species. E thermal E bond For a closed system : (Is it clear why theres no Q or W for a closed system?) For an open system : (Q and W can be positive or negative, as can Es.) E total = E 1 + E 2 + E 3 + ... = E total = E 1 + E 2 + E 3 + ... = Q + W Three New Energy Systems Rear shock absorber and spring of BMW R75/5 Motorcycle Kinetic energy is simply E moving . For translational energy, the indicator is speed ; the faster an object moves, the more KE it has. There is a quantitative relationship between KE and speed. Also, it is proportional to the mass of the object: The direction of motion of the object is unimportant. Baseball Work KE trans = m v 2 E total = E 1 + E 2 + E 3 + ... = Q + W Remember this equation for an open system? You have worked a lot with Q, Heat. Now we introduce Work: Work : A transfer of energy that takes place from a physical system to another physical system due to an interaction that involves a Force ....
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Lecture 3 intermLecture3forPosting - Physics 7A -- Lecture...

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