Science 8 Unit D: Mechanical Systems

1. Science 8 Unit D: Mechanical Systems

2. Topic 1.1 Learner Outcomes • Investigate and provide examples of mechanical devices used in the past to meet particular needs • Illustrate how a common need has been met in different ways over time • Identify components that operate as simple machines

3. Section 1.1 – Simple Machines – Meeting Human Needs • Early machines were very simple devices. • EX. Levers were used to pry rocks from the ground. • EX. Ramps were used to raise rocks to build walls. • First machines used humans or animals as sources of energy.

4. Class Discussion • What were the items in figure 1.1 use for historically? • How do the items work? • What needs were they designed to meet? • What is the approximate time period each were used in?

5. Moving Water Historically • No pumps to move water, so people used gravity. • Water stored in raised tanks, gravity caused it to move through the pipes and to the community. • Water and moved to raise tanks by water wheels (sakia) • a series of buckets attached to a long rope, which is draped over a large wheel •  Animals turned the wheel, which raised the buckets of water.

6. Sakia

7. Moving Water Historically • Archimedes made a more efficient way by developing the Archimedes screw. • Moves water by moving a screw. • Still used today with a grain auger.

8. Archimedes Screw

9. Simple Machines • Simple machines– tool or device made up of one basic machine • Every machine performs at least one of these functions. • The machine may: • Change the direction of a force • Multiply the speed or distance • Transfer the force from one place to another • Multiply force

10. Simple Machines • Make a chart like the one provided in the book on page 261 until it in as we go.

11. Your chart should look something like this (page 261)

12. 1. Lever • Rigid bar or plank that rotates around a fixed point called a pivot or fulcrum. • ADV: lever are used to reduce force needed to carry out a task • DISADV: to move a large load with a lever, you must move a greater distance than the load does

13. Lever

14. Lever Video

15. 3 Types of Levers • First class lever – fulcrum is between the load and the point where effort is exerted • EX. See saw, pry bar • Second class lever – load is between the effort and the fulcrum (fulcrum and the effort are at the opposite ends of the lever) • EX. Wheelbarrow • Third class lever – effort between the load and the fulcrum • EX. Arm, hammer

16. 3 Types of Levers GOOD FOR: Moving heavy loads EX. Crowbars and pliers GOOD FOR: Lifting heavy objects EX. Wheelbarrow GOOD FOR: Gaining speed EX. Hammer, your arm

18. Three Classes of Lever Video

19. 2. Inclined Plane • Makes it possible to lift heavy objects using smaller force • Also called a ramp • ADV: Uses a much smaller amount of force than if you did not use the ramp. • DISADV: Have to exert a force over a larger distance • DISADV: Often only used over small inclines – the steeper the ramp, the harder it is to control the object. • EX. Wheelchair access ramps

20. Inclined Plane

21. Inclined Plane Video

22. Inclined Plane Online Gizmo • LearnAlberta • Username: LA389 • Password: 9489 • Ant on a Slant • Try activity and answer the multiple choice questions afterwards. • Give Ms. Benard your score.

23. 3. Wedge • Similar to the inclined plane but used in a different way • Wedge machine is forced into an object. • ADV: Wedge increases the force that you apply on the object. • Press on wide edge of wedge to exert a force on the narrow end to split an object apart • DISADV: Wedge only pushes object apart (unlike a ramp which can be used to move objects up or down) • EX. Knives and axes

24. Wedge

25. Wedge Video

26. 4. Screw • Cylinder with the groove cut in a spiral on the outside. • Helps to increase the force you use • Penetrates materials was little force • Used to convert rotational motion to linear motion (grain auger) • Moves objects slowly.

27. Screw

28. Screw Video

29. 5. Pulley • Consists of wire, rope or cable moving on grooved wheel • Pulleys made of one or more wheels • Pulleys can be fixed in place or moveable • Pulley systems can be used to: • Reduce effort • Increase speed • Change direction

30. Pulley

31. Pulley Video

32. Pulley Online Gizmo • LearnAlberta • Username: LA389 • Password: 9489 • Pulleys (Piano, Armchair) • Try activity and answer the multiple choice questions afterwards. • Give Ms. Benard your score.

33. 6. Wheel and Axel • Combination of two wheels of different diameters that turn together • A longer motion on the wheel produces a shorter more powerful motion at the axel • Force advantage • Must turn more on the larger wheel to apply the force • EX. Steering wheel and steering column

34. Wheel and Axel • If force is applied to the axle and the load on the wheel, you can increase the speed. • Speed advantage • Must apply a large force to move the load • EX. Bicycle

35. Wheel and Axel

36. Wheel and Axel Video

37. Wheel and Axel Online Gizmo • LearnAlberta • Username: LA389 • Password: 9489 • Wheel and Axel • Try activity and answer the multiple choice questions afterwards. • Give Ms. Benard your score.

38. Video Review Quiz http://www.msichicago.org/fileadmin/Activities/Games/simple_machines/

39. Assignment • Complete Questions 1-4 on page 268

40. Topic 1.2 Learner Outcomes • Describing the overall function of the device • Describing the contribution of individual components or subsystems to the overall function of the device

41. Section 1.2 – The Complex Machine • Complex machines– a system where simple machines all work together • System – group of parts that work together to perform a function • Usually a complex machine • EX. Bicycle • Subsystem– group of parts that performed specific functions within a system • Usually a simple machine • EX. Pedal on the bicycle (lever)

42. Do give it a try, page 271

45. Complex machines move objects by transferring energy from one source to the object. • Subsystems that transfer force are: • Linkages • Transmissions

46. 1. Linkages • Belt or chain to directly transfer energy from energy source to an object • EX. Bicycle chain • You (the energy source) move your energy to the bicycle wheels (objects you want to move) by pedaling. Pedaling moves the chain which moves the bike tires. • Energy source Linkage  Object to move • High tension belts can also be used • EX. In a car motor

47. Linkages

48. 2. Transmissions • Special types of linkage • Transfer the energy from the engine to the wheels in large vehicles such as cars and trucks • Used to move much larger loads (transfers more force) • Contains many gears • Low gear = move slowly • High gear = moves quickly

49. Transmissions

50. Gears • Pair or series of wheels with teeth interlinked • When they rotate, one gear wheel transfers turning motion and force to the other. • Larger gearwheel moves more slowly than the smaller gearwheel, but it rotates with a greater force. • EX. Car • Gears also used to change the direction of motion • EX. Egg beater • Gears are important because they control the transfer of energy from one source to another. • EX. Rider to the bike tires • EX. Car engine to car tires