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


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