1. Work and Energy  Work done by a Force  Kinetic Energy  Potential Energy  Conservative Force  Non Conservative Force  Conservation of Mechanical Energy  Thermal Energy  Power  Machines Physics 150/250 Lesson 5

3. d  F || F

4. Total work done on an object is the sum of the work done by all forces on the object

8. An object in the Presence of Force can have POTENTIAL ENERGY which is the negative of the work done by the force in moving the object through a displacement d

9. It has Potential Energy if the work done by the force on the object does NOT depend on the path the force makes the object travel between two fixed points

10. If a force has this property it is called a CONSERVATIVE FORCE

11. In such cases Work Done on Object by Force = Change of Kinetic Energy of Object = Negative of Change of Potential Energy of Object due to the Force

13. Gravity IS a conservative force Friction is NOT a conservative force

14. initial position final position Force of Gravity d initial height h i final height h f

16. As W  K  U  K  U  0  K  U  We callK  U the Total Mechanical EnergyE of the object in the presence of a conservative force  E=0 Conservation of Mechanical Energy

17. If the force is non conservative Mechanical Energy is NOT conserved Frictional work generates Thermal Energy (Heat) (Non mechanical energy) Friction is non conservative Thus we cannot associate Potential Energy with Friction

18. change of kinetic energy of object

19. Power Rate of doing work Rate of changing energy

20. Machines  Ideal machines are 100% efficient  Simple machines can amplify forces