1. Energy Chap 4 Intro & Conservation

2. The Nature of Energy 4.1

3. What is Energy? Every change that occurs (large or small) involves energy. Changes are always taking place –  light bulbs are heating the air  the wind might be rustling leaves  cars are driving down the road

4. What is Energy? Energy is the ability to cause change.  Anything that causes change must have energy. The SI unit for energy is the joule (abbreviated J)

5. Nature of Energy ENERGY motion of electric charges bonding of atoms motion of objects internal motion of particles changes in the nucleus The ability to cause change. MECHANICAL ELECTRICAL CHEMICAL NUCLEARTHERMAL joules (J)

6. An Energy Analogy If you had $1000, you could  put it in your wallet  put it in the bank  trade it for gold  exchange it for travelers’ checks Regardless of its form, money is money.

7. An Energy Analogy In the same way, energy is energy – regardless of its form.  Energy from the Sun that warms you and energy from the food that you eat are only different forms of the same thing.

8. Nature of Energy Kinetic Energy (KE)  energy a moving object has because of its motion  depends on mass and velocity

9. Nature of Energy KE = ½ mv 2  KE increases as mass increases  KE increases as speed increases 80 km/h 50 km/h 80 km/h 80 km/h truck 50 km/h motorcycle Which has the most KE? Which has the least KE?

10. Nature of Energy Potential Energy (PE)  stored energy  depends on position or configuration of an object

11. Nature of Energy Which boulder has greater gravitational PE? What other ways can an object store energy? PE = mgh  PE increases as mass increases  PE increases as height increases

12. Potential Energy There are several types of PE:  Elastic PE Stretched rubber band  Chemical PE Gasoline (bonds)  Gravitational PE anything that can fall increases with height and mass

13. KE or PE? An apple in a tree has PE. An apple falling from a tree has KE.

15. Conservation of Energy 4.2

16. Conservation of Energy Law of Conservation of Energy  Energy can change from one form to another, but the total amount of energy never changes.

17. 6 Forms of Energy  Mechanical  Thermal Energy  Chemical Energy  Electrical Energy  Electromagnetic Energy  Nuclear Energy

19. Transforming Energy Light bulbs transform electrical energy into light and heat.

20. Transforming Energy An engine transforms the chemical PE stored in gasoline molecules into the kinetic energy of a moving car or bus.  spark plug fires (chemical PE into thermal energy)  Hot gases expand (thermal energy into kinetic energy)

21. Transforming Energy Some energy transformations are less obvious (no visible motion, sound, heat, or light) Green plants convert light energy from the Sun into energy stored in chemical bonds in the plant

22. Conservation of Energy PE  KE  The form of energy changes, but the total amount of energy remains the same. View pendulum animation.pendulum animation

23. Conservation of Energy If energy is conserved, why do swings eventually slow to a stop?  Mechanical  Thermal View rolling ball animations.rolling ball animations

24. Your Body and Energy Everybody, raise both hands. In terms of energy, what happened?  PE  KE Every second, chemical PE (stored when you eat) is converted into:  Heat (constant body temperature and given off to surroundings)  Other daily functions (heart beat, digesting, walking, etc.)

25. Your Body and Energy The food Calorie (C) is a unit used to measure how much energy you get from foods.  1 C = 4184 J  1 g of fat = 9 C  1 g of carbs or protein = 4 C

26. Video and VLab http://www.brainpop.com/science/en ergy/formsofenergy/ http://www.brainpop.com/science/en ergy/formsofenergy/ http://www.brainpop.com/science/en ergy/kineticenergy/ http://www.brainpop.com/science/en ergy/kineticenergy/ http://glencoe.mcgraw- hill.com/sites/0078779626/student_v iew0/unit1/chapter4/virtual_lab.html http://glencoe.mcgraw- hill.com/sites/0078779626/student_v iew0/unit1/chapter4/virtual_lab.html

27. Self-Check 4 1. 3 gram ball on a top shelf and a 3 gram ball on a bottom shelf. Which has more PE? 2. 2 gram ball and 6 gram ball move at 3 m/s. Which has more KE? 3. Friction converts ___________ energy into _________ energy. top 6 g mechanical thermal