The Nature of Energy

1. The Nature of Energy

2. Energy • Every change that occurs involves . • Moving objects have energy • You can tell an object has energy when it: • Changes its environment • Changes itself • Energy • Electrical – moving electrons • Chemical – from bonds • Thermal- heat

3. Energy • Energy exists in many different forms • It may look different, but it’s still energy. • Examples: fire, movement, gasoline in a bucket • Demo Question #1: What is making the can move back and forth? • Question #2: Where is the energy coming from?

4. Energy Types • Kinetic energy- energy in the form of motion • Depends on mass and velocity of an object • Increase in either mass or velocity = increase in energy • KE =1/2 mv2 • Units = kg*m2/s2 • KE = ½ mv2 Velocity changes will impact KE more because velocity is squared.

5. Types of Energy • Potential Energy – energy of position • Energy in stationary objects and bonds • Elastic Potential Energy – Energy of compression or stretching • Chemical Potential Energy – Energy stored in bonds • Gasoline, food, hand warmers • http://www.youtube.com/watch?v=Jnj8mc04r9E&feature=related

6. Types of Energy • Gravitational Potential Energy- Energy stored due to position above the surface of Earth • Depends on mass of object, height of object above ground, and acceleration due to gravity • GPE = m x h x a • All energy – measured in units of Joules • 1 J = 1 kgm2/ s2 • Energy can be converted: • As an object falls, GPE decreases and KE increases

7. Law of Conservation of Energy • Energy cannot be created or destroyed. • E is constant in universe • Can only be transformed from one type to another • Energy can be transformed into non-useful forms, like heat • “Disappearing energy” – doesn’t disappear • Is converted into thermal energy by friction

8. Demo #2 Question #1: Where is the energy come from? Question #2: How does this demonstration illustrate the Law of Conservation of Energy? Question #3: At what point in the pendulum's swing is its gravitational potential energy highest? Question #4: Describe the point at which the kinetic energy of the pendulum is highest.

9. Changing Forms of Energy • Many devices convert energy from one form to another • Electrical to thermal • Mechanical to Electrical • In Vehicles: • Engine: Chemical Energy to Kinetic energy • Spark plug: Electrical Energy converts gasoline’s chemical energy to thermal energy • Thermal Energy causes gases to expand • Expanding is mechanical energy, which moves parts of the car = kinetic energy

10. Conversions Between Forms of Energy • Plants: light into chemical • Uses E from sunlight to make bonds • Mechanical energy – total KE and PE in a system • ME = KE + PEG + PEe • Amount of ME is due to: • Position and Motion • Can PE be converted into KE?

12. Pra

14. Practice problems for kinetic and potential energy What is the kinetic energy of a car with a mass of 500 kg and a speed of 5 m/s? What is the GPE of a person standing at the top of a ladder with a height of 15 meters? The person has a mass of 80 kg.

15. Practice continued… What is the kinetic energy of a child on a swing with a mass of 30 kg and a speed of 3 m/s? What is the GPE of a bowling ball with a mass of 1.5 kg and held 2 meters above the ground?

16. Resources Roller coaster Animation: http://www.physicsclassroom.com/mmedia/energy/ce.cfm http://www.youtube.com/watch?v=0ASLLiuejAo&feature=related