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

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

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)

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

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

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

CLASS ACTIVITY: 1.What is the formula used for WORK DONE? 2.How much work did Jo do to push his toy car 6.4m with a force of 15N? 3.If Jo needed 45J to push his car 8m, then how much force did he need? 4.If Jo used 56N of force & 62J of work, then how far did he push his toycar?

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

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)

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)

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

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

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.

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

SINGLE-SECOND CLASS LEVERS: -DEFINITION: -When Load (L) is between Fulcrum (F) & Effort (E) -Always gives some kind of M.A.

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

LINKED SINGLE-SECOND CLASS LEVERS: -DEFINITION: -Formed when 2 nd 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

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

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

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

CLASS ACTIVITY: Identify the 3 different classes of levers (Let’s do this together) – first draw the 3 lever classes AB C

GEAR SYSTEMS

-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

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

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

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

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

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

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

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

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

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

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

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

Term 3 Topic 3 Unit 2: Mechanical advantage calculations

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 What we do on the 1 side we do on the other side Find videos of ratios

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

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

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

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: Means: force had a MA over the load i.e. the force moved 1 x for every 4 x that the load moved

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

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

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

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 = Force Find pic of thinking caps

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

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

- 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

M.A. CALCULATIONS USING TOOTH RATIOS FOR GEARS: Gear ratio (velocity ratio) = number of teeth of driven number of teeth of driver Calculate the gear ratio if the driven gear has 60 teeth & the driver gear has 15 teeth Let’s see who can do this first!! =D

M.A. CALCULATIONS USING TOOTH RATIOS FOR GEARS ANSWER: Gear ratio (velocity ratio) = number of teeth of driven number of teeth of driver Gear ratio = 60 = 4 = 4 : This means that the MA ratio is 4:1 So the driven gear turns 4 x more than the driver gear

CALCULATING GEAR WHEEL DIAMETER FOR GEARS: A gear’s most NB feature is that gears of unequal sizes (diameters) can be combined to produce a MA -A different arrangement of different gear sizes = a ‘gear ratio’ -& the number of teeth / gear diameter is used as the units -Let’s determine the MA of a particular gear combination Find pics & video of gear trains & MA for gear combinations

CALCULATING GEAR WHEEL DIAMETER FOR GEARS: MA = output force input force Calculate the MA if the output force is 60 N & the input force was 40 N Answer: MA = 60 N = 1 = 1 N : 1.5 N N 1.5 N

CALCULATION USING VELOCITY RATIOS (i.e. gear ratios): Velocity Ratio = Driver gear (the one connected to the power) Driven gear We use the number of teeth of the gears to calculate VR (velocity ratio)

CALCULATION USING VELOCITY RATIOS (i.e. gear ratios): Then: We want to calculate the speed of the driven gear So: Our VR = 12 = 1 = If driven speed = rpm Then final speed = rpm x VR (i.e. 0.5) = 500 rpm

CALCULATION USING VELOCITY RATIOS EXTRA EXAMPLE: Let’s see if you can do this one by yourself =D The driver gear has 60 teeth The driven gear has 30 teeth What is the VR? If the driven speed is rpm? What is the final speed of the driven gear?

CALCULATION USING VELOCITY RATIOS EXTRA EXAMPLE ANSWER: VR = driver = 60 = 2 = 2 0r 2, driven 30 1 Driven speed = rpm So final driven speed = rpm x VR = rpm x 2,0 = rpm

Term 3 Topic 3 Unit 3: COMMUNICATION & DESIGN SKILLS

REPRESENTING GEAR SYSTEMS GRAPHICALLY: GRAPHICALLY DEFINITION: Show a design through drawings, sketches, plans & diagrams COUNTER ROTATING Turning in opposite directions How would we graphically represent this???

Find pics of gears graphically represented

REPRESENTING GEAR SYSTEMS GRAPHICALLY: IDLER GEARS INBETWEEN SPUR GEARS Let’s graphically represent this Find pics of spur gear with idler gear graphically represented with rotation directions

REPRESENTING GEAR SYSTEMS GRAPHICALLY: How would we represent the DRIVEN GEAR turning faster & turning slower???? Find pics of driven gear turning faster & slower graphically (look for driven gear being bigger & smaller than driver gear)

IMPORTANT TERMS: OUTPUT VELOCITY DEFINITION: The rate of speed of the output from an electronic device FORCE MULTIPLIER DEFINITION: Something that makes a given force more effective than that same force would be without it Find pics output velocity & force multipliers