1. Chapter 14 Work, Power, & Machines

2. Sec. 14.1 Work & Power

3. What is work? Work is done when a force acts on an object in the direction the object moves Work (J)= Force (N) x distance (m) W = F x d SI unit: Joule  Joule = Nm

4. Work requires Motion If there is no motion…there is no work Some motion must be in the direction of the force Since there is no motion, there is no work

5. What is Power? Power is the rate at which work is done.  Doing work faster requires more power Power (w) = Work (J) / Time (s) P = W / t SI unit: watt  Watt = J/s

6. Horsepower 1 horsepower = 746 watts Based on the power output of a very strong horse

7. Sec. 14.2 Work & Machines

8. What is a Machine? A machine makes doing work easier. How?  Change the size of the force  Change distance over which the force acts  Change the direction

9. Increasing Force & Distance Work = Force x Distance Increasing the Force causes a decrease in distance Increasing Distance causes a decrease in force

10. Work Input & Work Output Work Input = Input Force x Input distance W in = F in x d in Work Output = Output Force x Output distance W out = F out x d out Due to friction: W in > W out

11. Ideal Machine Contains No Friction!!! W in = W out

12. Sec. 14.3 Mechanical Advantage & Efficiency

13. Mechanical Advantage The number of times the machine increases an input force 2 types of Mechanical Advantage  AMA (Actual Mechanical Advantage) Measure actual forces in a machine  IMA (Ideal Mechanical Advantage) Measure with out friction (in an ideal machine)

14. Calculating AMA Actual Mechanical Advantage = output force input force AMA = F out / F in

15. Calculating IMA Ideal Mechanical Advantage = Input distance Output distance IMA = d in / d out

16. AMA versus IMA The AMA is always greater than the IMA because friction is present. Engineers try to design machines with low- friction materials & lubricants.

17. Efficiency The percent of work input that becomes work output Efficiency = (W out / W in ) x 100% Due to friction: Efficiency is always less than 100%

18. Sec. 14.4 Simple Machines

19. 6 Types of Simple Machines 1. Lever 2. Wheel & Axle 3. Inclined Plane 4. Wedge 5. Screw 6. Pulley

20. Lever A rigid bar free to move around a fixed point (fulcrum) IMA = Input arm / output arm  Input arm: distance between F in and fulcrum  Output arm: distance between F out and fulcrum

21. First Class Lever Fulcrum is located between the input force & output force Ex. Seesaw, scissors, tongs MA: can be: >1, <1 or =1

22. Second Class Lever Output force is between the input force & fulcrum Ex. Wheelbarrow MA is >1

23. Third Class Lever The input force is located between the fulcrum and output force Ex. Baseball bat, hockey stick, golf club MA is <1

24. Wheel & Axle Consists of two disks or cylinders  Each has a different radius  Wheel: outer disk  Axle: inner disk IMA = r wheel / r axle Gears are a modified wheel & axle

25. Inclined Plane A slanted surface along which a force moves an object to a different height IMA = distance / change in height

26. Wedge A v-shaped object whose sides are 2 inclined planes Thin wedge of a given length has a greater IMA then a thick wedge of the same length Examples: zipper, knife blades, door stop

27. Screw An inclined plane wrapped around a cylinder The closer the threads, the greater the IMA

28. Pulley A rope that fits into the groove in a wheel IMA = # of ropes supporting the load  Pull down - don’t count  Pull up - count Changes the direction of the force

29. 3 Types of Pulleys Fixed: wheel attached to a fixed location Movable: wheel attached to object Pulley System: combination of fixed & movable pulleys Fixed pulley Movable pulley

30. Block & Tackle Pulley system containing both fixed and movable pulleys

31. Compound Machines A combination of 2 or more simple machines Example: Honda Ad http://www.steelcitysfinest.com/HondaAccordAd.htm