1. Work and Energy

2. Definition
Work is defined as a force acting on an object to cause a displacement.
Notice that the force must cause a displacement in order for there to be any work. If person pushes on an object all day and the object never moves, they have not done any work.

3. No work is done unless there is a displacement

4. Types of Work
Positive
Negative

5. Perpendicular Force

6. Force at an Angle

7. Linear Work (F constant)
W = Fdcosq F q d
The unit of work is the joule (J)

8. Parallel Component F q
Fcosq d

9. Work by a non-constant force
Work is the area under the F vs. x curve

10. Work = change in mechanical energy
Work Energy Theorem
W = DE
Work = change in mechanical energy

11. Mechanical Energy
Mechanical Energy is the energy associated with the position (Potential Energy) or motion (Kinetic Energy) of an object or system.

12. AP Work Equation

13. Conservative Force A force is conservative if:
The work done between point A and B is independent of the path
The work done around any closed path is zero

14. Conservative Forces
Gravity
Elastic (Spring)
Electromagnetic

15. Conservation of Mechanical Energy
If the only work done on an object is by a conservative force, then the mechanical energy of the object is conserved.

16. Non-Conservative Forces
Friction
Drag (Air Resistance)
Other Resistive Forces

17. Example
A horizontal force of 50.0 N is applied to a 30.0 N box as it is pulled a distance of 8.0 m along the floor. The coefficient of friction between the box and the floor is 0.12.
What is the work done by the applied force?
What is the work done by friction?
What is the work done by the net force?

18. 1)

19. 2)

20. 3)