GCSE Physics (AQA)

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Gear Ratios

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Forces Moments, levers and gears

Gear Ratios

4:56 Applying Moments
Spec 4.5.4
Previous Gears Next Distance & Displacement
  • Gears transfer moments through contact forces as their teeth move past each other.
  • The radii of gears can be compared using ratios.
  • Example: Two smaller gears have a radius of 0.4 meters, and a larger gear has a radius of 0.6 meters.
  • Ratios can be scaled like fractions to compare sizes.
  • The ratio of gear radii can be calculated by multiplying each radius by five, resulting in a ratio of 2:3:2.
  • The moment experienced by each gear follows the same ratio as their radii.
  • Moments are the turning effect from a force, calculated as force multiplied by perpendicular distance (radius for gears).
  • Input force is required for gears to start turning, with a reaction force at each contact point.
  • The time for a gear to complete one rotation follows the same ratio as the radii.
  • Larger gears take longer to complete a rotation due to larger circumference.
  • The ratio of rotation times is the same as the ratio of circumferences and radii.
  • The number of teeth on each gear follows the ratio to maintain rotational frequencies.
  • The ratio of teeth is the same as the ratio of radii, as teeth depend on circumference.
  • Example problem: Calculate the moment on a gear with 32 teeth given an input force on a gear with 8 teeth.
  • Steps to solve: Determine teeth ratio, calculate larger gear radius, determine reaction force, calculate moment.
  • Moment calculation: Moment = Force x Radius; for larger gear, 5 newtons x 0.6 meters = 3 Newton meters.

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