Chapter 7 Review

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

This preview shows pages 1–7. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

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. ...
View Full Document

## This note was uploaded on 02/12/2012 for the course PHYSICS 104 taught by Professor Staff during the Fall '10 term at Rutgers.

### Page1 / 7

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

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online