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Announcements

Announcements. *3 rd Exam on Thursday, November 3 rd * Homework for tomorrow… (Ch. 10, Probs 4, 5, & 6) 9.26: W = -37 J 9.34: W = -6 J Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm

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Announcements

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  1. Announcements • *3rd Exam on Thursday, November 3rd * • Homework for tomorrow… (Ch. 10, Probs 4, 5, & 6) 9.26: W = -37 J 9.34: W = -6 J • Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm • Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm • 6th Annual Smashing Pumpkins Event - Monday @ noon, outside of Tomlinsion Library • Extra credit due on Tuesday

  2. Chapter 10 Potential Energy & Energy Conservation (Work & Path Dependence and Potential Energy )

  3. Different forms of Energy • Kinetic • Potential • Thermal • Light (radiant) • Sound

  4. Dissipative Forces Energy is ‘lost’ to friction by an object which goes into… • heating • sound Friction is a dissipative or nonconservative force

  5. Work done by Gravity What is the work done by gravity on the box which slides down the incline a distance ?

  6. Conservative and Nonconservative Forces Nonconservative Force… • Generally dissipative • Work done by a nonconservative force depends on the path • i.e. frictional force Conservative Force… • Work done by a conservative force is independent of the path • i.e. gravitational force, spring force

  7. General Statement about Conservative Forces… The net work done by a conservative force on a particle moving around any closed path is zero For a conservative force:

  8. Defining Potential Energy Change Potential energy change for a conservative system is defined as the negative of the internal work the system does on itself when it undergoes a reconfiguration. Potential energy is stored work!

  9. y Gravitational Potential Energy The work required to lift a box of mass m a height y is W = mgy. Where does this work go?  into Gravitational Potential Energy

  10. Gravitational Potential Energy cont.. Notice: • Potential energy is stored energy waiting to be ‘let loose’. • Potential energy is a relative energy… The zero-reference level is arbitrary & must be chosen. • Can only measure a change in PE.

  11. Spring Potential Energy The work required to stretch a spring a distance x2 is This can be recast as spring potential energy

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