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