1. Work, Power, and Simple Machines Video #57 (simple mach. For kids)
Chapter 15
Work, Power, and Simple Machines
Video #57 (simple mach. For kids)

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)
Video #44 (Science of Golf)

6. 15-3 Machines
*device that makes work easier
Video #42 (Real World: W,E,F)

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

8. -effort and resistance
*work input(Wi): work done on a machine
-Wi = Fe X de
Ex: crowbar

9. -effort and resistance
*resistance force(FR): force applied by the machine
*Work output(WO): work done by a machine

10. -effort and resistance
*resistance distance(dr): dist through which the object moves
-Wo = FR X dR
-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 = FR / FE

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 = WO / WI 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
1st class: multi effort force and also change dir
Ex: pliers, scissors, seesaws

25. -levers
2) 2nd class: resist force is between the fulcr and the effort force
-multi eff force but does not change dir
Ex: wheelbarrow, door, nutcracker

26. 3) 3rd class: eff force > resistan -doesn’t multi force
-levers
3) 3rd 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. -1st and 2nd levers mult the eff force -3rd levers multi the distance
-MA = eff arm length
resist arm length
-1st and 2nd levers mult the eff force
-3rd levers multi the distance

29. -pulleys video #43 (pulley simple machines)
-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. *is a combination of 2 or more simple machines.
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!
Video: 49 (pumkin chuckin)