Changing Magnitude & Direction of Force (AQA GCSE Design & Technology): Revision Note

Using levers

First-order lever

• Fulcrum is positioned between the load and effort

• Examples: seesaw, scissors/pliers, crowbar

• A longer effort distance makes lifting the load easier

• A shorter effort distance makes lifting the load harder

Second-order lever

• The load is positioned between the fulcrum and effort

• Examples: wheelbarrow, nutcracker, bottle opener

• Increased effort-to-load distance provides greater force on the load

• Decreased effort-to-load distance provides a lesser force on the load

Third-order lever

• Effort is positioned between the fulcrum and load

• Examples: tweezers, fishing rod, shovel

• Increased effort-to-fulcrum distance provides greater force on the load

• Decreased effort-to-fulcrum distance provides lesser force on the load

Using linkages

Bell cranks

• A two-arm linkage joined by a pivot at an angle

• Designed to change the direction of force or movement

• Arm length and angle can be adjusted for varied results

• Uses: vehicle steering, bicycle brakes, window mechanisms

Push/pull linkages

• Linkages which transfer straight-line force

• Push involves compression; pull involves tension

• Direction and force magnitude can be adjusted via layout and length

• Uses: bicycle and car brakes, mechanical toys, door handles, garden machinery

Using rotary systems

Cams and followers

• A cam is a rotating cylinder or disc which moves a follower

• A follower is a straight component which is moved by the cam

• Cams convert rotary motion into linear or reciprocating motion

• Circular cam: produces steady, even motion

• Pear cam: produces rapid rise and fall with a steady base

• Snail-shell cam: produces sudden drops with slight rises (requires a roller)

• Uses: car engines, sewing machines

Simple gear trains

• A set of two or more gears which rotate in line

• Gears have teeth that "mesh" together, turning in opposite directions, which transfers motion

• Gear ratio is calculated from the tooth count relationship

  • Example: 12 teeth ÷ 6 teeth = 2:1 ratio

• Driver gear: initiates movement (typically connected to a motor)

• Idler gear: adding this between the driver gear and another gear reverses the direction again

  • It rotates in the opposite direction to the driver so the final gear turns in the same direction as the driver gear

• Driven gear: rotates in the same direction as the driver

• Smaller gears rotate faster than larger gears

Pulleys and belts

• A pulley is a wheel with a groove for a belt, connected to an axle

• A belt is a flexible material which transfers motion between pulleys

• Grooved belt and pulley: basic system

• Geared pulley and belt: a teeth-based system for greater accuracy