1. Chapter 6 Work and Energy 6.1 – Work Work Formula & Units Positive & Negative Work 6.2 – Work-Energy Theorem & Kinetic Energy KE Formula & Units 6.3 – Gravitational Potential Energy GPE Formula Positive & Negative Work 6.4 – Conservation of Energy Total Mechanical Energy 6.5 – Power Power Formula

2. Work is done on an object whenever a force is applied parallel to the displacement. 6.1 – Work Done by a Constant Force Work = Force x Displacement

3. Less work is done on the object in bottom figure.

4. displacement (m) force (N) work (N·m or Joule)

5. θ = 0°; cosθ =1 W = F(s) θ = 90°; cosθ = 0 W = 0 θ = 180°; cosθ = -1 W = - F(s) θ = 270°; cosθ = 0 W = 0 Block is moving this way 

6. Person is doing positive work on the barbell when lifting. Person is doing negative work on the barbell when lowering

7. Work can be positive or negative, but it is NOT a vector. Work is measured in Joules (Newton- meters) or ft-lbs

8. 1. Lifting a weight up off the floor. Are you doing work on the object? 2. Pushing a truck as hard as you can but the truck doesn’t move 3. Carrying books across a room. 4. Lowering a barbell during a bench-press rep. 5. Gravity pulling a ball down to earth. 6. Gravity pulling on a book resting a table. YES YES, negative work YES NO

9. For now, a good way to know if work is done is to see if the PE or KE of the object is changed. Work will cause a change in energy of the object.

10. Ch. 6 Homework #1 Ch. 6 Problems #1-5 (p. 180)

12. Energy - The ability to do work; measured in Joules Kinetic Energy -Energy due to motion mass (kg) velocity(m/s) 6.2 – Work-Energy Theorem & KE

14. The Work-Energy Theorem - A net external force on an object changes the KE of the object. The change in KE of the object equals the work that was done on the object W = ΔKE

15. Ch. 6 Homework #2 Ch. 6 Problems #12,13,15,17 p. 181

16. Potential Energy - Energy due to relative position Elastic Potential Energy Electrical Potential Energy Gravitational Potential Energy

17. 6. 3 - Gravitational Potential Energy Work done by the force of gravity height difference (m)

18. Gravitational Potential Energy height (m) The work done by gravity does not depend on the path taken, only the height difference.

19. The total mechanical energy (E) of an object remains constant, neglecting frictional forces. E = KE + PE 6. 4 – Conservation of Mechanical Energy E initial = E final

21. The Kingda Ka is a giant roller coaster with a vertical drop of 127 m. Suppose that the coaster has a speed of 6.0 m/s at the top of the drop. Neglect friction and air resistance and find the speed of the riders at the bottom in miles/hour

22. Chapter 6 Homework #3 Ch. 6 Problems #25,26,28,35,32,36 page 182

23. Power - the rate at which work is done. 1 horsepower = 550 ft-lbs/sec = 745.7 watts 6. 5 – Power

24. Conservation of Energy Lab When block is moving up or down at constant velocity, the net force is zero. F up = F grav + f k F down = F grav - f k F up + F down = 2 (F grav )

25. Conservation of Energy Lab 4. Work = F grav x length 1. W = mg 2. F grav = (F up + F down ) /2 3. F grav = Wsinθ 5. ΔPE = mgh 6. Work actual = F up x length

26. Ch. 6 Equations E = KE + PE E initial = E final