1. Unit 5 - Work and Energy CHAPTER 8 CONCEPTUAL PHYSICS BOOK CHAPTER 6 PHYSICS BOOK

2. Part 2 CONSERVATION OF ENERGY AND POWER

3. Conservative vs. Nonconservative Forces  Conservative force – total Work on a closed path is zero. (ex: gravity)  Nonconservative force – total Work on a closed path is NOT zero. (ex: friction) Energy 3 -W+W -W Gravity- down Motion- up Friction – left Motion - right Friction - right Motion- left Gravity- down Motion- down

4. Conservation of Energy

5. Conservation of Mechanical Energy

6. Conceptual Example 1: Pendulum  Pendulum - Kinetic and Potential Energy Pendulum - Kinetic and Potential Energy  In the absence of air resistance and friction…  the pendulum would swing forever  example of conservation of mechanical energy  Potential → Kinetic → Potential and so on…  In reality, air resistance and friction cause mechanical energy loss, so the pendulum will eventually stop.

7. Conceptual Example 2: Roller Coaster  Roller Coaster - Kinetic and Potential Energy Roller Coaster - Kinetic and Potential Energy

8. With Non-Conservative Forces…

9. Conceptual Example 3: Downhill Skiing  Downhill Skiing - Kinetic and Potential Energy Downhill Skiing - Kinetic and Potential Energy  This animation neglects friction and air resistance until the bottom of the hill.  Friction is provided by the unpacked snow.  Mechanical energy loss (nonconservative force)  Negative work

10. Problem Solving Insights  Determine if non-conservative forces are included.  If yes: ME f = ME 0 + W nc (We won’t be solving this type)  If no: ME f = ME 0  Eliminate pieces that are zero before solving  Key words: starts from rest (KE 0 = 0), ends on the ground (PE f = 0), etc.

11. Example 1  A 2.00kg rock is released from rest from a height of 20.0 m. Ignore air resistance & determine the kinetic, potential, & mechanical energy at each of the following heights: 20.0 m, 12.0m, 0m (Round g to 10 m/s 2 for ease)

12. Example 1 - Answers HeightKEPEME 20.0 m 0 J2*10*20 = 400 J400 J 12.0 m 400-240 = 160 J2*10*12 = 240 J400 J 0 m 400-0 = 400 J2*10*0 = 0 J400 J Start Here Then Use This

13. Example 2 Find the potential energy, kinetic energy, mechanical energy, velocity, and height of the skater at the various locations below. 13 Energy max

14. Example 2 - Answers 14

15. Power

16. Power Example #1

17. Power Example #2

18. Power Example #3

19. Power Example #4