1. Energy Physics December 9/12/13

2. Objectives Define mechanical energy Define kinetic and potential energy Describe the work-energy theorem State the law of conservation Evaluate how energy is conserved Evaluate a proof for the work-energy theorem

3. What is Energy? Topic Energy Facts The “something” that enables an object to do work Measured in Joules (J) We will focus on mechanical energy

4. Reach for the Stars Topic What else have we learned that is measured in Joules? Facts Work

5. What is Mechanical Energy? Topic Mechanical energy Facts The energy due to the position (potential energy) of something, or the movement (kinetic energy) of something

6. Making Connections Topic What does it mean when someone says you have a lot of potential? Facts

7. Potential Energy Topic Potential energy Facts Energy stored and held in readiness – Something at rest – Something high off the ground Symbol is PE Units are Joules (J) PE = mgh – m = mass (kg) – g = gravity (10 m/s 2 ) – h = height/distance (m) – PE= potential energy (J)

8. Kinetic Energy Topic Kinetic energy Facts Energy of motion Symbol is KE Units are Joules (J) KE = ½ mv 2 – m = mass (kg) – v = velocity (m/s) – KE = kinetic energy (J)

9. Potential or Kinetic Energy? Topic A car parked on the street. A car driving down the street. A rock falling from a mountain. Facts PE KE

10. Work-Energy Theorem Topic What is the relationship between work and energy? Facts Whenever work is done, energy changes Work = change in Energy

11. Reach for the Stars Topic Use the equation for work and PE to show how I can say: W = PE Facts W = PE Fd = mgh – since W = Fd – Since PE = mgh mgd = mgh – Since F = mg *which are the same

12. Conservation of Energy Topic When is energy conserved? Facts ENERGY IS ALWAYS CONSERVED! Energy is transferred from PE to KE and vice versa

13. Let’s take a closer look at the conservation of energy Topic Figure 8.7, page 110 Facts

14. Explain the teacher demo Topic Why don’t I get hit in the face? Facts

15. Making Connections Topic Remember when we dropped things. What was the initial velocity before dropping? Why then is something at rest have no KE? Facts

16. Closing Topic Use the following words to describe what is happening with the swinging pendulum. PE KE Conservation of energy Work Work-energy theorem Facts

17. Challenge Topic Can anyone prove why: Fd = ½ mv 2 Note: ignore the 1/2 Facts

18. More Practice- on website! Use the equations for PE and KE to solve PE = mgh KE = ½mv 2 Handout #5, 6, 8a