Chapter 6

1. Chapter 6 Work, Energy, Power

2. Work • The work done by force is defined as the product of that force times the parallel distance over which it acts. • The unit of work is the newton-meter, called a joule (J) • Work is a scalar

3. q Work s cos q

4. q Work F cos q

5. Energy • Types of Energy • Kinetic Energy = “Motion Energy” • Potential Energy = “Stored Energy”

6. Kinetic Energy • Kinetic Energy is the energy possessed by an object because it is in motion.

7. Gravitational Potential Energy • Gravitational Potential Energy is the energy possessed by an object because of a gravitational interaction.

8. Properties of GravitationalPotential Energy • Arbitrary Zero Point • You need to select a zero level • Independent of Path • All that matters is the vertical height change

9. Conservation of Mechanical Energy • Energy can neither be created nor destroyed, but only transformed from one kind to another. Works for systems with no losses (friction, air resistance, etc.)

10. Work Energy Theorem • The amount of kinetic energy transferred to the object is equal to the work done. DKE = W • Many of the problems can be worked from here

11. Problem Solution Guidelines • Determine that energy can be conserved (no losses) • Pick the zero level for potential energy • Pick two interesting places in the problem • Write kinetic and potential energies at these places • Conserve energy • (KE + PE)1 = (KE + PE)2

12. Power • Power is the time rate of doing work.

13. Power • The unit of power is a joule per second, called a Watt (W).

14. On to problems...