1. Chapter 15 Work, Power, and Simple Machines

2. 15-1 Work *force acting through a distance -Work = force X distance -W = F X d -Units: newton-meter(N-m) or Joule(J)

3. 15-2 Power *how fast work is done -Power = work / time -P = W / t or P = F X d / t

4. 15-2 Power -Units: N-m / s or J / sec or watt (W) -1J/sec = 1 watt -1000 watts = 1 kilowatt(kW)

5. -Horsepower *(hp) = to 750 watts (745.56)

6. 15-3 Machines *device that makes work easier

7. -effort and resistance -make work easier by changing size or dir of applied force *effort force(F e ): force applied to a machine

8. -effort and resistance *work input(W i ): work done on a machine -W i = F e X d e Ex: crowbar

9. -effort and resistance *resistance force(F R ): force applied by the machine *Work output(W O ): work done by a machine

10. -effort and resistance *resistance distance(d r ): dist through which the object moves -W o = F R X d R -Machines do not multi work, they can multi force -Worko is never greater than worki

11. -mechanical advantage *(MA) # of times a machine multi the effort force -MA = F R / F E

12. -mechanical advantage -MA is not always greater than1, sometimes = to 1,

13. -mechanical advantage -MA of one changes the dir of the effort force -MA is less than 1, increases the dist an object is moved or the speed with which it is moved

14. -efficiency *comparison of worko to worki - Efficiency = W O / W I X 100 -High eff = worki is changed to worko -eff can never be greater than 100%

15. -role of friction -less friction = higher its effic -effic can be increased by reducing friction ex: oil, grease, wax,bearings

16. 15-4 Simple Machines -6 simp mach: incline plane, the wedge, the screw, the lever, the pulley, and the wheel and axle

17. -inclined plane *slanted surface used to raise an object(a ramp) -smaller effort force, but moved through a greater distance

18. -inclined plane -MA = length of the plane divided by its height -length can never be shorter than its height -MA = never be < 1

19. -wedge and screws *wedge: incline plane that moves -large force exerted on a small surface

20. -wedge and screws -longer and thinner the less effort force required ex: sharpening

21. -wedge and screws *screw: an incline plane wrapped around a cylinder to form a spiral -multi an effort force by acting through a long effort distance -the closer the threads > the MA

22. -levers *bar that is free to pivot about a fixed point when effort force is applied ex: seesaw, shovel, nutcracker, crowbar *fulcrum: is the fixed point

23. -levers -3 classes of levers -based on the position of the fulcrum, effort force, resist force

24. -levers 1)1 st class: multi effort force and also change dir Ex: pliers, scissors, seesaws

25. -levers 2) 2 nd class: resist force is between the fulcr and the effort force -multi eff force but don’t changed dir Ex: wheelbarrow, door, nutcracker

26. -levers 3) 3 rd class: eff force > resistan -doesn’t multi force -multi dist of eff force

27. -levers -MA: # of times the lever increases the eff force *effort arm: dist from the eff force to the fulc *resist arm: dist from resis force to the fulc

28. -levers -MA = eff arm length resist arm length -1 st and 2 nd levers mult the eff force -3 rd levers multi the distance

29. -pulleys -can change either dir or amount of eff force -fixed pulley: attached to a stationary object -can’t multi eff force -change dir of eff force

30. -pulleys -MA of a fixed pulley is 1

31. -pulleys -movable pulley: -can multi eff force -can’t change dir of an eff force -MA>1

32. -pulleys -can predict MA by counting the number of supporting sections of rope.

33. Complex Machines *is a combination of 2 or more simple machines. **you can get no more work out of a machine than you put in it!