ZIMSEC O Level Combined Science Notes: Machines: Gears

  • A gear is a toothed wheel
  • These toothed wheels transfer motion to one another using their teeth
  • GearsĀ are also known as cogs wheels
  • The teeth on a gear are also known as cogs
  • These cog wheels are usually mounted on shafts
  • The teeth of adjacent cogs fit the grooves of the cog next to it
  • This is known as meshing
  • The teeth of two or more cog wheels mesh into each other
  • When one of the gears rotates motion is transferred to the next gear by these teeth


Meshed gears

Meshed gears

  • In machines such as a vehicle’s gear box the gears have different cogs (teeth)
  • When a vehicle is in low gear there are more cogs in one wheel than the other
  • This changes the velocity ratio
  • In the example above the larger gear has 24 cogs while the smaller wheel has 12 cogs
  • In this case the smaller gear is the effort gear
  • While the larger gear is the load gear
  • The velocity ratio in this case is found using the formula:
  • \text{ Velocity Ratio= } \dfrac{\text{Number of teeth on load gear}}{\text{Number of teeth effort gear}}
  • VR=\dfrac{24}{12}
  • 2
  • This means the smaller gear turns twice for each time the load gear turns
  • If a car’s gear lever is used to move the car into a higher gear
  • Different gears are meshed for example as shown above
  • Each of these gears has 14 teeth
  • The Velocity Ratio is thus:
  • VR=\dfrac{14}{14}
  • 1
  • The Mechanical advantage is also found using the formula above
  • Assuming a friction of 0
  • The Mechanical Advantage is the same as the Velocity Ratio of the gears

To access more topics go to the Combined Science Notes pag

Quick NetOne, Econet, And Telecel Airtime Recharge