Chapter 7 Review

Chapter 7 Review - Chapter 7 Lecture Essential University...

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Unformatted text preview: Chapter 7 Lecture Essential University Physics Richard Welfeen 2nd Editien Conservation of Energy Conservative and Nonconseryatiye Forces - A oonaaryatiya foroa atoraa any work done against it, and can “give back” the stored work as kinetic energy. - For a conaawatiya foroa, the work done in rnoying between two points is inolapandant of the path: - Baoauaa the work done by a oonaaryatiya force is path independent, the work done in going around any ofoaad path is zero: if i [BF-wza - A nonoonaaryatiya foroa does not store work done against it, the work done may dapanal on path, and the work done going around a closed path naaol not be zero. Potential Energy - The “atcred wcrk” aaacciated with a ccnaeryatiye fcrce is called pctential energy. — Pctential energy ia atcred energy that can he released as kinetic energy. - The change in pctential energy is defined as the negative at the wcrk dcne by a ccneeryatiye fcrce acting cyer any path between twc pcinta: 3.. flUflz—AF-df — Pctential energy change is independent cf path. — Only changes in pctential energy matter. — We’re free tc set the aerc cf pctential energy at any canyenient pcint. Two Common Forms of Potential Energy - Gravitational potential energy stores the work done against gravity: fiU: mg .fly 5 — Gravitational potential energy increases linearly with height y. — This reflects the constant gravitational force near Earth's surface. Potential energy. if ' ii I Iciglu. _i' - Elastic potential energy stores the work done in stretching or compressing springs or t' spring-like systems: U : 53mg — Elastic potential energy increases quadratically with stretch or compression )6. — This reflects the lineany increasing spring force. "k. = [3" _ {.‘uiiiliru-isinn Eiquifihriuin le-L'Iuli spring’s equilibrium configuration. Conservation of Mechanical Energy - By the work-energy theorem, the change in an object’s kinetic energy equals the net work done on the object: AK = Wmat - When only conservative forces act, the net work is the negative of the potential-energy change: Wm,1t = —AU - Therefore when only conservative forces act, any change in potential energy is compensated by an opposite change in kinetic energy: AK + AU = 0 - Equivalently, K + U = constant = Kfl + U.;} - Both these equations are statements of the law of conservation of mechanical energy. - A spring—loaded dart gun - A spring and gravity — What’s the oert’s speed? — How high does the block go? mon- / Ir ' floor; j: _ L ' | 5:: IL Eff; ‘ __ Es __ __ __ ' IJI' JVI *1 :45 4:: ' K+ U: Kn + Ufl becomes émv2+020+éh2 ' SO vzqfk/mx wherexisthe initial spring - So 3: compression. - K+ U: KtI + Ufl becomes 0+ring?!:0+%k:r2 hi 22mg Force and Potential Energy - Force is greatest where potential energy increases most rapidly. - Mathematically, the component of force in a given direction is the negative derivative of the potential energy with respect to position in that direction: At peaks and valleys. there's no force. E a; l‘orcc is grcatcr F dU Li: Wi'lILtt'L? this. triii's't: : — — = + I ' ' 'i. I. 'i. ' Is hiLJLpt. t. I It: dx E H E C3 E‘— _ Position, .1: its-"hen the {Lii'vt is rising In IilL‘ right. l'an‘t' is 1H tho fi'fi. ...
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This note was uploaded on 02/12/2012 for the course PHYSICS 104 taught by Professor Staff during the Fall '10 term at Rutgers.

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Chapter 7 Review - Chapter 7 Lecture Essential University...

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