Gear

Key Stage 2

You can change the gears on a bicycle to make it easier to go up a hill.

Gears are circular disks with 'teeth' that lock together with other gears to change how quickly they spin.

Gears are used in bikes, cars, and any engine which turns.


The speed can be made bigger by turning the larger gear. The small gear will turn more quickly.

Gears are circular disks with 'teeth' that can act to increase the speed or the moment of a force.

A small gear turning a large gear acts to decrease the speed and increase the moment.

A large gear turning a small gear acts to increase the speed and decrease the moment.

Gears are circular disks with 'teeth' that can act to increase the speed or the moment of a force.

The multiplying effect of gears can be found by the ratio of the radii or the number of 'teeth'.

A gear with few teeth turning a gear with many teeth acts to decrease the speed and increase the moment.

A gear with many teeth turning a gear few teeth acts to increase the speed and decrease the moment.

The force on one gear is equal in magnitude to the force applied to the other gear.

A gear with radius 50mm is turned with a moment of 10Nm. This gear used to turn a second gear with a radius of 20mm. Calculate the moment of the second gear.	A gear with 45 teeth is turned with a moment of 25Nm. This gear used to turn a second gear with a 63 teeth. Calculate the moment of the second gear.	A gear with 144 teeth is turned with a moment of 72Nm. This gear used to turn a second gear with 60 teeth. Calculate the moment of the second gear.
1. State the known quantities Moment = 10N Radius 1 = 50mm = 0.05m Radius 2 = 20mm = 0.02m	1. State the known quantities Moment = 25Nm Teeth Ratio = 45:63	1. State the known quantities Moment = 70Nm Teeth Ratio = 144:60
2. Substitute the numbers into the equation and solve. \(M = Fd\) \( 10 = F \times 0.05\) \( F = 200N\) An equal force applies to the second gear. \( M = F \times d\) \( M = 200 \times 0.02\) \( M = 4Nm\)	2. Substitute the numbers into the equation and solve. \( M = \frac {25}{45} \times 63\) \( M = 35Nm\)	2. Substitute the numbers into the equation and solve. \( M = \frac {72}{144} \times 60\) \( M = 30Nm\)