Lecture10_Pushkar_2011

Lecture10_Pushkar_2011 - Lecture 10 Purdue University...

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Unformatted text preview: Lecture 10 Purdue University, Physics 220 1 Lecture 10 Potential Energy and Energy Conservation PHYSICS 220 Lecture 10 Purdue University, Physics 220 2 Potential Energy • Work done by gravity is independent of path • W g = -mg (y f- y i ) = - ∆ PE g • Define PE g = mgy • Only the difference in potential energy is physically meaningful, i.e., you have the freedom to choose the reference (or zero potential energy) point. • Works for any CONSERVATIVE force • There is a fact, or if you wish, a law, governing natural phenomena that are known to date. There is no known exception to this law; it is exact, so far we know. The law is called conservation of energy; it states that there is a certain quantity, which we call energy, that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number, and when we finish watching nature go through her tricks and calculate the number again, it is the same. Richard Feynman Lecture 9 Purdue University, Physics 220 3 Lecture 9 Purdue University, Physics 220 4 Energy • Energy is “conserved” meaning it can not be created nor destroyed – Can change form – Can be transferred • Total Energy of an isolated system does not change with time • Types – Kinetic Energy – Potential Energy – Rest Energy (E=mc 2 ) – Thermal Energy – … … • Units: Joule (J) = N m = kg m 2 / s 2 Lecture 10 Purdue University, Physics 220 5 Work by Variable Force W = F x ∆ x Work is the area under the F vs x plot-W= ∆ PE s = 1/2 k x 2 Spring: F spring = -k x Potential Energy: Lecture 10...
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This note was uploaded on 04/10/2011 for the course PHYS 220 taught by Professor Chang during the Spring '09 term at Purdue.

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Lecture10_Pushkar_2011 - Lecture 10 Purdue University...

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