# Mechanical Systems

Cards made for AQA GCSE Resistant Materials on mechanical systems

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• Created by: Lucy :)
• Created on: 31-05-13 09:58

## Mechanisms

• they change input moton into output motion
• designed so you can gain an advantage from using them
• some change 1 type of motion to another
• there are various types of motion:
• Linear motion
• moving one way in a straight line
• Reciprocating motion
• moving backwards + forwards in a straight line
• Oscillating motion
• moving backwards + forwards in an arc
• Rotary motion
• moving in a circle
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## Gear Trains

• gear trains transmit rotary motion
• gears = toothed wheels that interlock
• gear train = 2 or more gears linked together
• if the driver gear turns the driven gear they will turn in different directions
• if you use a 3 gear (called an idler) the driver + driven gear will turn in same direction
• ^idler won't alter the speed of the other 2 gears
• If the linked gears are different sizes they will turn at different speeds (one half the size will go quicker)
• a compound gear train = more than 1 gear fixed to the same shaft
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## Gears changing the motion

Rack + Pinion

• used to turn rotary into linear motion
• the pinion (a round gear) is turned to move a flat gear (the rack)
• used on railways on steep sections of track to stop wheels slipping backwards

A Worm Drive + Worm Wheel

• changes the direction of rotation through 90o
• used for tightening guitar strings

Bevel Gears

• also changes direction of rotation through 90o
• the teeth are angled at 45o so the gears fit together at right angles
• used in hand drills

EXAM TIP!! You might be asked to sketch and name it's parts so look up images of mechanisms

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## More mechanisms

Belt Drives

• transfer movement from 1 rotating shaft to another
• used in pillar drills
• flexible belt links the motor to the drill shaft

Chain + Sprocket

• used on a bike
• advantage = can't slip like a belt drive could
• made up of 2 sprockets - the size effects the speed

Pulleys

• 1 on its own changes the direction of the force required
• same amount of force needed but pulling might be easier than lifting
• 2 or more can make things feel lighter than they are
• e.g. 1 fixed pulley + 1 moving pulley (a block + tackle) results in half the force needed to lift
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## Cams

• change rotary motion to reciprocating motion
• has 2 main parts - the cam + the follower
• they come in many different shapes + sizes
• they always rotate
• the follower rests on the cam + follows its shape
• ^ it may have a small wheel to reduce friction
• basic cam shapes:
• Circular cam (also called offset or eccentric) - produces a uniform reciprocation motion
• Snail cam - for half a turn the follower won't move then it will gently rise + suddenly drop, will only work in 1 direction
• Pear cam - for half a turn the follower won't move then it will gently rise + fall
• Four-lobed cam - has 4 lobes (looks like a toy flower windmill) for each turn the follower will rise + suddenly fall 4 times, will only work in 1 direction
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## Levers

First Class leavers

• load one end, have a pivot in the middle, effort the other
• makes the load easier to lift
• pivot closer to the load = easier to lift
• e.g. = sisors

Second class leavers

• pivot at one end of the leaver + effort at the other end
• e.g = wheelbarrow
• closer together pivot + load = easier to lift

Third class leavers

• effort is in between the load + the pivot
• e.g = fishing rods, cricket bats, garden spades
• moving effort + pivot further apart = easier
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