What is a wheel
A wheel is a special type of lever. Each spoke of the wheel is a lever, the axle is the fulcrum and the rim is the outer end of the lever.
What is a pulley
A pulley is a wheel with a groove around it in which ropes or chains can wrap around. Pulleys are easier to exert a downward force. In order to increase the amount of force, we increase the amount of pulleys. e.g block and tackle, yacht, flags and blinds.
What are gears
- Gears are like wheels with teeth.
- Gears transfer motion into force.
- Gears can be meshed together or can be joined be a chain or a belt.
- A set of gears are also known as a gear train
- Force = Driving Gear=Driven gear
Force multiplier
If gears were force multipliers, the driving gear (the smaller gear) is before the driven gear (the bigger gear). The driving gear spins fast while the driven gear spins slow, this increases the force. This means, the gears are gearing down. e.g going uphill (car, bike), gearing down.
Speed Multiplier
If gears were speed multipliers, the driving gear (the bigger gear) is before the driven gear (the smaller gear). The driving gear spins slow while the driven gear spins fast. This increases the speed. This means the gears are gearing up. e.g gearing up, egg beater
Calculating the gear ratio
The gear ratio of sprockets on a bicycle, or of two gears meshed together on a machine, is calculated by dividing the number of teeth on the driving sprocket (or driving gear) by the number of teeth on the driven sprocket (or driven gear).
The low gear combination shown in Figure 8.3.10 has 12 teeth on the driving sprocket and 24 on the driven sprocket. The gear ratio is 12 ÷ 24 = 0.5. This means the rear sprocket spins through half a revolution for every turn of the chain wheel.
The high gear combination shown in Figure 8.3.11 has the opposite combination.
Its gear ratio is 24 ÷ 12 = 2. This means that for each turn of the chain wheel, the rear sprocket turns twice.
The low gear combination shown in Figure 8.3.10 has 12 teeth on the driving sprocket and 24 on the driven sprocket. The gear ratio is 12 ÷ 24 = 0.5. This means the rear sprocket spins through half a revolution for every turn of the chain wheel.
The high gear combination shown in Figure 8.3.11 has the opposite combination.
Its gear ratio is 24 ÷ 12 = 2. This means that for each turn of the chain wheel, the rear sprocket turns twice.