Machines: Gears

• A gear is a toothed wheel
• These toothed wheels transfer motion to one another using their teeth
• Gears 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

• 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

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