describe the types of linkages (3) and how linkages work
- 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
describe how cams work
- 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
name the different cams (5)
- 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
state the four types of motion
- reciprocating - up+down or side-side
- oscillating - side-side about a fixed position
- rotary - in a circle
- linear - in one direction
name the functions used in flow charts+ their symbol/shape (4)
- start/end - rounded rectangle
- input/output - rhombus
- process - rectangle
- decision - diamond
+ arrows - connect shapes
describe first order levers
fixed pivot is in the middle
eg. see-saw
-> the closer the fixed pivot is to the load, the easier it is to lift
describe second order levers
load is in the middle
eg. wheel barrow
-> the closer the fixed pivot is to the load, the easier it is to lift
describe third order levers
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
describe gears and gear trains
- 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
describe uses of pulleys
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
