1. Energy Elastic Potential Energy Systems Power Varying Forces

2. Elastic Force, F s, is Conservative Force required to stretch/compress spring Force is _____________ to the amount of stretching or compression (____________) Newton’s 3 rd Law means the spring exerts an ______ ____ ___________ force The force is described by Hooke’s Law It is a ___________ force

3. Potential Energy Stored in a Spring The average restoring force exerted by a spring when compressed (or stretched) is: x i = 0x f = −x F1F1 F0F0

4. Elastic Potential Energy Include work done by spring in work-energy theorem

5. Systems and Energy Conservation The total amount of energy in the universe remains _________. Energy can _______ _____, but it can never be created or destroyed. Apply to a ________ of objects that changes from initial state to final state. The system may, in general, have energy transferred into or out of it (___________).

6. Systems W c changes ____ Rewrite in terms of mechanical energy If E changes, it goes somewhere For example, friction creates thermal energy

7. Nonisolated Systems Energy is transferred into or out of the system Ways to transfer energy Work Heat Mechanical Waves Electrical Transmission Electromagnetic Radiation

8. Power Power is the _____ _____ of energy transfer The energy transfer can change over time Δt so we use the average power Unit is Watt: 1 W = 1 J/s = 1 kg  m 2 /s 3

9. Power Energy (or work) is sometimes listed in terms of power · time Electricity usually billed for kilowatt-hours (kWh) U.S. units are the horsepower (hp)

10. Varying Forces For small displacements  x, F x nearly __________ Add up all small rectangles Work is _____ under graph Fig. 5.28, p. 148

11. For A Spring Compress or stretch _________ (no heat) Work is done by applied force Spring does same work (but it’s ____________) Change in potential energy is negative of work done by spring Fig. 5.29, p. 148