Term 3 Topic 3 Unit 1: Mechanical systems & control (machines, levers & their functions)

1. Term 3 Topic 3 Unit 1: Mechanical systems & control(machines, levers & their functions)

2. MACHINES ARE ABLE TO: • Increase amount of force to move a bigger load • This machine = FORCE MULTIPLIER • Increase distance that object moves • This machine = DISTANCE MULTIPLIER

3. FORMULA FOR AMOUNT OF WORK DONE: Work = Force x distance W = F x d J = N x m Amount of work done (W) = measured in Joules (J) Force (F)  measured in Newtons (N) Distance (d)  measured in metres (m)

4. EXAMPLE: • Wheelbarrow is pushed 50 m • Using a force of 20 N • How much work has been done? Let’s see who can find this answer first!!! =D

5. EXAMPLE ANSWER: Wheelbarrow is pushed 50 m = distance (d) in m Using a force of 20 N = force (F) in N How much work has been done? = Work (W) in J Therefore W = F x d W = 20 N x 50 m W = 100 Nm or 100 J

6. CLASS ACTIVITY: • Car is moved 85 m • Using a force of 120 N • How much work has been done? Let’s see who can find this answer first!!! =D On the board!

7. CLASS ACTIVITY: • What is the formula used for WORK DONE? • How much work did Jo do to push his toy car 6.4m with a force of 15N? • If Jo needed 45J to push his car 8m, then how much force did he need? • If Jo used 56N of force & 62J of work, then how far did he push his toycar? On the board!

8. MECHANISMS: • DEFINITION: • Different parts working together to perform a specific task • They are the parts that make work easier • Convert INPUT force to an OUTPUT force

9. A JACK used on a CAR: • Turn the screw of jack = INPUT force • Jack raised higher = PROCESS • Car lifted up = OUTPUT force • Is the jack a force multiplier or a distance multiplier??? = FORCE MULTIPLIER (makes it easier to lift car)

10. Please BRING for next class: 1 long pencil Glue roll (stick)

11. MECHANICAL SYSTEM: • DEFINITION: • When a machine uses a mechanical appliance (like the screw of the jack) to provide force for movement • OTHER MACHINES THAT USE OTHER SYSTEMS: • Electrical systems (work with electricity) • Hydraulic systems (work with liquid under pressure) • Pneumatic systems (work with air under pressure)

12. A D CLASS ACTIVITY Label the following as either: Hydraulic Or Pneumatic Or Electrical B E C F

13. LEVERS: • DEFINITION: • Bar free to turn about a fixed point or pivoting point (FULCRUM) • Are simple machines • 3 classes: • A) first class levers • B) second class levers • C) third class levers

14. SINGLE-FIRST CLASS LEVERS: • DEFINITION: • When fulcrum (F) lies between Load (L) & Effort (E) • Mechanical advantage (M.A.): • Depends on position of fulcrum • If F closer to L than E, then will be M.A. let's draw!

16. LINKED FIRST-CLASS LEVERS: • DEFINITION: • Some cases 2 levers linked together at fulcrum e.g. pair of scissors • Normal paper scissors  blades equal in length to handle = NO M.A • Pruning scissors  long handle & short, strong blades = M.A. greater than 1 • Express as MA > 1 • i.e. less force to get work done

17. SINGLE-SECOND CLASS LEVERS: • DEFINITION: • When Load (L) is between Fulcrum (F) & Effort (E) • Always gives some kind of M.A. let's draw!

19. SINGLE-SECOND CLASS LEVERS: • IMPORTANT: • If given MA > 1 • Means output force is bigger (>) than input force • i.e. when person presses lever they use less force to get the work done

20. LINKED SINGLE-SECOND CLASS LEVERS: • DEFINITION: • Formed when 2nd class levers joined at fulcrum • E.g. office punch • Gives M.A. > 1 (what does this mean?) • Why??? • F fixed at a point where operator needs less Effort to perform the task let's test this with 1 piece of paper & 7 pieces of paper

21. SINGLE-THIRD CLASS LEVERS: • DEFINITION: • Effort (E) is between Fulcrum (F) & Load (L) • Never gives Mechanical Advantage (M.A. < 1) • i.e. requires more effort than Weight of Load • E.g.’s: • Fishing rod • Light duty stapler • Pair of tweezers let's draw!

22. SINGLE-THIRD CLASS LEVERS: • IMPORTANT: • Often small movement at 1 end will produce a larger movement at the other end • E.g. fishing rod

23. LINKED THIRD-CLASS LEVERS: • DEFINITION: • Formed when 3rd class levers joined at fulcrum • E.g. office stapler • M.A. < 1 • Why??? • Effort too close to fulcrum to give a greater M.A.

24. CLASS ACTIVITY: Identify the 3 different classes of levers (Let’s do this together) – first draw the 3 lever classes On the board! C A B

25. GEAR SYSTEMS

26. FORCE DEFINITION: • Make things move • TORQUE DEFINITION: • Force applied that causes an object to rotate around an axis • COUNTER ROTATION: • 2 wheels rotating in opposition directions • i.e. a gear consist of 2 such wheels let's draw!

27. GEARS: • Transfer rotating movement • DIFFERENCE BETWEEN GEAR & PULLEY??? • Gears have teeth which directly engage with each other & prevent 2 wheels from slipping

28. SPUR GEARS or straight cut gears: • DEFINITION: • Consist of a disk with teeth projecting from inside outward • Edge of each tooth is straight • When spur gears mesh / join • smaller gear = PINION • Bigger gear = WHEEL

29. SPUR GEARS or straight cut gears: • 1 gear turned by motor = DRIVER gear • Driver gear meshes with other gear • Second gear = DRIVEN gear • Often spur gears are unequal sizes • This means different numbers of teeth for each • M.A. now produced let's draw!

30. SPUR GEARS or straight cut gears: • Smaller gear  rotates faster vs bigger gear • BUT • Bigger gears TORQUE is greater (although turns slower)

31. HOW TO CALCULATE GEAR RATIO aka VELOCITY RATIO • Gear ratio = number of teeth of the driven gear ----------------------------------------- number of teeth of the driven gear • Velocity ratio is also used for gear ratio

32. CLASS ACTIVITY: Lets work out the Velocity ratio of the spur gear below (let’s see who can do it first =D) Don’t forget your ratio value & statement On the board!

33. BICYCLE (spur gear) EXAMPLE: • Pedal gear = front gear  DRIVER GEAR • Differs in size to back gear  DRIVEN GEAR • Changing Velocity ratio  forces cyclist to use more force on driver gear

34. TWO SPUR GEARS CONNECTED VIA AN IDLER GEAR: • GEAR TRAIN DEF: • Made up of 2 or more gears • 1st gear may rotate clockwise • 2nd gear may rotate anti-clockwise • 3rd gear would rotate in direction of 1st gear • Often gears in Gear train are different sizes & will rotate at different speeds let's draw!

35. TWO SPUR GEARS CONNECTED VIA AN IDLER GEAR: • IDLER GEAR: • Forces 2 outer gears to turn in same direction • Called SYNCHRONISATION • NOTE: • Could also make size of shape the size to have them turn at the same velocity

36. SUITABLE MATERIALS: • IDLER GEAR FUNCTION: • Influence rotation of 2 important gears • Therefore Idler gear much smaller than other 2 gears & found between driven & driver gear • Bears all force & wear of other 2 gears • MUST BE: strong, hard material that wont break / affect speed & functioning of the other 2 gears

37. TWO BEVEL GEARS: • When linked together transfer axis of rotation through 90° • i.e. change direction of drive through 90° • Have cone-shaped teeth cut at 45° angle • E.g. hand drill mechanism Find pics / videos of working bevel gear

38. Term 3 Topic 3 Unit 2: Mechanical advantage calculations

39. RATIOS: • DEFINITION: • Describes a relationship between 2 things in numbers • i.e. the relative sizes of 2 or more things • What does the ratio of 4:3 mean?? • E.g. there could be 4 oranges for every 3 apples • If there are now 8 oranges • Then 4 oranges x 2 = 8 oranges • So 3 apples x 2 = 6 apples Find videos of ratios What we do on the 1 side we do on the other side

40. LEVERS & MECHANICAL ADVANTAGE: • Levers give us mechanical advantage • This means: • Levers help us lift heavy weights with little effort

41. SPEED RATIO: Speed ratio = distance moved by force (effort) ----------------------------- distance moved by load

42. SPEED RATIO EXAMPLE: Calculate the speed ratio of the mechanism if the distance moved by the force was 20 & the distance moved by the load was 80 Let’s see who can do this first!! =D On the board!

43. SPEED RATIO EXAMPLE ANSWER: Speed ratio = ??? Our formula: speed ratio = distance moved by the force --------------------------------- distance moved by the load Speed ratio = 20 = 1 = 1: 4 ------ ---- 80 4 Means: force had a MA over the load i.e. the force moved 1 x for every 4 x that the load moved

44. SPEED RATIO EXAMPLE: What does this really mean??? Every 1 time the forefinger moved (i.e. its distance moved), the eraser moved 4 times Therefore the lever is a DISTANCE MULTIPLIER! Find pic of eraser on a lever system

45. MECHANICAL ADVANTAGE OF A MECHANISM: MA = load ----- force Load & force are both measured in Newtons (N) Newtons = unit of force Find videos of newtons

46. MECHANICAL ADVANTAGE OF A MECHANISM EXAMPLE: Calculate the MA of a mechanism with a load of 40 and a force of 70. Let’s see who can do this first!! =D Find pics of load & effort On the board!

47. MECHANICAL ADVANTAGE OF A MECHANISM EXAMPLE ANSWER: Calculate the MA of a mechanism with a load of 40 and a force of 70. MA = ??? MA = Load = 40 = 1 ------- ------ ------ Force 70 1.75 Find pic of thinking caps

48. 1 NEWTON: A force that is 1 N strong = the weight of 100g mass e.g. you experience 1 N of force when you hold a 100g slab of chocolate So how many Newtons would you experience with a 650 g slab of chocolate??? = 6.5 N (i.e. 650g / 100 g = 6.5N) Find pics of slab of chocolate

49. M.A. CALCULATIONS FOR GEARS USING RATIOS: • When we mesh 2 gears together, they act similar to levers • Each end of a gear’s tooth = similar to the end of a lever with a fulcrum at the gear’s centre • Longer lever A is  greater the force applied to the shaft of the driven gear Find pics & video of MA for gears using ratios let's draw!

50. SHAFT DEFINITION: • Drive shaft that transfers torgue (i.e. turning motion of a gear around a fixed point) • Gears DO NOT ONLY increase speed & change direction • BUT they also MULTIPLY TURNING FORCES