Systems

Question 1

describe the types of linkages (3) and how linkages work

Answer 1

• push/pull or parallel linkage: uses two fixed pivots, input+output motions act in the same direction whereas the motion of link is in the opposite (toolbox with drawers)
• bell crank: changes the direction of a force through 90 degrees (bike brakes)
• reverse motion: changes direction of input so output goes opposite way (foldable clothing drying lines)
  -> changing the position of the fixed pivots changes the magnitude of the output force
  -> moving pivots connect the linkage and allow movement

Question 2

describe how cams work

Answer 2

• the follower rests on the cam as it rotates and follows its shape
• cams change rotary motion to reciprocating motion: the cam rotates so the follower moves up and down
• changing the size or shape of a cam will change the magnitude of the reciprocating motion of the follower

Question 3

name the different cams (5)

Answer 3

• circular (offset/eccentric) - produces a uniform reciprocating motion, the pivot is placed off-centred to cause the follower to move up and down
• snail - the follower will gently rise and the suddenly drop, only works in one direction
• pear - will not move for half a turn then will gently rise and fall
• four-lobed - has four lobes that stick out, each turn the follower will rise and fall suddenly 4 times, only works in one direction
• heart - follower rises+fall uniformly

Question 4

state the four types of motion

Answer 4

• reciprocating - up+down or side-side
• oscillating - side-side about a fixed position
• rotary - in a circle
• linear - in one direction

Question 5

name the functions used in flow charts+ their symbol/shape (4)

Answer 5

• start/end - rounded rectangle
• input/output - rhombus
• process - rectangle
• decision - diamond
  + arrows - connect shapes

Question 6

describe first order levers

Answer 6

fixed pivot is in the middle
eg. see-saw

-> the closer the fixed pivot is to the load, the easier it is to lift

Question 7

describe second order levers

Answer 7

load is in the middle
eg. wheel barrow

-> the closer the fixed pivot is to the load, the easier it is to lift

Question 8

describe third order levers

Answer 8

effort is in the middle
eg. spade/ fishing rod/cricket bat

-> moving effort and fixed pivot further apart makes it easier to lift the load

Question 9

describe gears and gear trains

Answer 9

• used to transfer direction of rotary motion or change magnitude of input force
• 2 gears -> driver+driven will turn in opposite directions
• 3 gears (driver+idler+driven) -> driver+driven will turn in the same direction
• gears with fewer teeth (smaller) will turn faster

Question 10

describe uses of pulleys

Answer 10

makes lifting a load easier
- one pulley: changes direction of force required, eg. pulling down is easier than up
- two pulleys: changes direction+magnitude of force required, makes load feel lighter than it is

can have fixed pulleys or moving pulleys