ME 242 Lecture 18 03.11

ME 242 Lecture 18 03.11 - ME 242 Dynamics Today's Key...

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1 ME 242 Dynamics March 11, 2009 Eric Wang Today’s Key Concepts Chapter 4: Energy of Particles Positive vs. Negative Work Conservative forces Potential energy Positive vs. Negative Work • Positive work increases KE of system • Negative Work decreases KE of system KE 2 = KE 1 + W 1 2 Two Ways to determine sign (+/-) of Work • Visual • Mathematical W A B = mgj 0 h dy j = mgh W B A = h 0 dy j = mgh W A B = mgh W B A = mgh B h A mg dy j i Not that kind of Conservative… Conservative Forces Definitions: • A force is conservative if the work done by the force is path independent . • A force is conservative when it does no net work on an object moving around a closed path, starting and finishing at the same point. Implications: • The work done by a conservative force is totally reversible • You can get out exactly what you put in
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2 No net work for a closed path 60 Joules -60 Joules A B Work done by gravity g y 1 x 1 y 2 x 2 y 3 x 3 y 4 W A B = mg ( y
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This note was uploaded on 09/19/2009 for the course ME 242 taught by Professor Kam during the Spring '06 term at Nevada.

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ME 242 Lecture 18 03.11 - ME 242 Dynamics Today's Key...

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