Wheels, Pulleys and Gears 8.3

Wheels  Centre of a wheel is called the axle  The outside the wheel is the rim  A wheel is a special type of lever:  Each spoke of the wheel is a lever  The axle is the fulcrum  Wheel rim is the outer end of the lever  Centre of a wheel is called the axle  The outside the wheel is the rim  A wheel is a special type of lever:  Each spoke of the wheel is a lever  The axle is the fulcrum  Wheel rim is the outer end of the lever

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Pulleys  A wheel with a groove.  Changes a downwards force into an upwards motion.  Using two pulleys halves the size of the effort force required providing a mechanical advantage of 2.  A number of pulleys in an arrangement called a Block and Tackle

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Gears  Gears are wheels that have teeth around their rim.  A set of gears are called a Gear Train  The gear that supplies the force is the Driving Gear the gear connected is the Driven Gear  Different gears are chosen to either increase the force or the speed of turning  Gears are wheels that have teeth around their rim.  A set of gears are called a Gear Train  The gear that supplies the force is the Driving Gear the gear connected is the Driven Gear  Different gears are chosen to either increase the force or the speed of turning AZJJ0

Gear as a force multiplier  The driving gear is smaller than the driven gear  This is called gearing down  The driving gear is smaller than the driven gear  This is called gearing down

Gears as a speed Multiplier  The driving gear is smaller than the driven gear  This is called gearing down

Types of gears Type of gearFunctionExample Bevel Gear Positioned at right angles to each other so that they change the plane of rotation Hand drills: as the handle is turned in a vertical direction, this is transferred into rotation of the drill bit in a horizontal plane Worm Gear Looks like a screw, and is used to drive a gear. Is often used to reduce speed Used to tune a guitar string Rack and Pinion A gear wheel rotates over a row of teeth, called the rack. This converts rotational motion into straight-line (or linear) motion Used to convert steering wheel rotation into linear motion to the right or the left in order to turn the wheels of the car Idler Gear Positioned between a driving and a driven gear to get them rotating in the same direction Engaging an idler gear between two gears in a car with manual transmission allows the car to reverse