3.2 Conservation of Energy

1. 3.2 Conservation of Energy pp. 70 - 72 Mr. Richter

2. Agenda • Warm Up • Review HW • Notes: • Conservation of Energy • Solving Conservation of Energy Problems • “Conserving” Energy • Problem Solving Practice

3. Objectives: We Will Be Able To… • Describe the changes of potential and kinetic energy of an object as it changes height. • Solve problems with conservation of energy. • Understand the difference between conservation of energy in physics and “conserving” energy in real life.

4. Warm-Up: • As an object falls, it loses its potential energy (because it loses height). Where does that energy go? Does it disappear? Does it go somewhere else? • On a half sheet of paper, write your name and 2-3 sentences answering the questions above. You have 5 minutes.

5. Conservation of Energy

6. Conservation of Energy • The total amount of energy in a system does not change. • The Law of Conservation of Energy: • Like momentum, this is only true in the absence of outside forces, like friction.

7. Conservation of Energy • When objects are moving upward, they lose kinetic energy but gain potential energy. • Kinetic energy converts into potential energy. • When objects are moving down, they lose potential energy but gain kinetic energy. • Potential energy converts into kinetic energy.

8. Let’s Watch a Quick Video

9. Problem Solving with Conservation of Energy • In general, the law of conservation of energy means that: • if you know the kinetic energy at one point, you know the potential energy at another point or vice versa • You will be given a speed, and asked how high an object will travel • Or you will be given a height, and asked how fast an object will be traveling at the bottom

10. Problem Solving with Conservation of Energy • A 2-kg car moving with a speed of 2 m/s starts up a hill. How high does the car roll before it stops? • Hint: find the kinetic energy at the bottom of the hill first. Then use the potential energy at the top of the hill to find the height of the hill.

11. “Conserving” Energy

12. “Conserving” Energy • In real life, when we say conserve energy, we usually mean: • turn off the lights when you leave the room • buy a fuel-efficient car • This is to “save” energy. • However, that energy is not really lost. It is just converted to forms that it is difficult to convert back from. • It is easy to turn electricity into heat and light. It is more difficult to turn the heat and light from a light bulb back into electricity.

13. Wrap-Up: Did we meet our objectives? • Describe the changes of potential and kinetic energy in an object as it changes height. • Solve problems with conservation of energy. • Understand the difference between conservation of energy in physics and “conserving” energy in real life.

14. Homework • Worksheet #2, 3, 6, 7, 8, 9, 11 due Thursday • Notebook and Research due Tomorrow.