1. Energy Ch. 5

2. Energy I. Energy – the ability to do work (or cause change) Most energy can be classified into 2 general categories:

3. Energy 1. Potential energy (PE) – stored energy or energy of position PE = mgh mass (kg) 9.8 m/s 2 height (m)

4. Energy 2. Kinetic Energy (KE) – energy of motion KE = ½ mv 2 mass (kg) velocity (m/s)

5. Energy 3. The unit for energy is Joules (J). James Prescott Joule 1818-1889

6. Energy Types TypeKE vs PE DescriptionExamples Mechanical Energy Both Energy associated with motion and position of everyday things Speeding train, Bouncing ball, Sprinting athletes Thermal (Heat) Energy KE Energy is the motion of particles (faster = more heat) Candles, electric heaters

7. Energy Types TypeKE vs PE DescriptionExamples Chemical Energy PE Stored in chemical bonds in compounds (broken bonds – PE Increases) Gasoline, food, battery Radiant Energy KE Energy of electromagnetic waves, including light Solar energy X-rays Radio waves

8. Energy Types TypeKE vs PE DescriptionExamples Sound Energy KE Energy that moves through substances (compression waves) Music, Pencil hits floor, etc Electrical Energy KE Movement of electrical charges Electricity in wires, lightning

9. Energy Types TypeKE vs PE DescriptionExamples Nuclear Energy PE Energy that is stored in the nucleus (holds p + & neutrons together) Sun (fusion), Powerplants (fission)

10. Law of Conservation of Energy A. Energy may change forms but it cannot be created or destroyed B. If energy is conserved, then  PE =  KE (  is “change in”) C. Conservation of Mechanical Energy: (KE + PE) beginning = (KE + PE) end D. Energy flowchart shows how energy changes form.

11. Law of Conservation of Energy a. The life of Stretchy the Rubber Band: Stretchy is pulled – KE  PE Stretchy is released – PE  KE Stretchy is broken – KE  heat & sound

12. Energy Problems Examples: What is the potential energy at points A through E?

13. Energy Problems To demonstrate a cheerleading stunt, Miss Rokosik has to lift Miss Kalousek over her head (to a height of 2 m). Miss Kalousek has a mass of 50 kg. What is the potential energy of Miss Kalousek?

14. Energy Problems What is Miss Kalousek’s kinetic energy while she is held above the ground?

15. Energy Problems Miss Rokosik gets tired and drops Miss Kalousek from the 2 m height. What is her kinetic energy just before she hits the ground? How do you know?