Fig 22 shows the gear system on a bicycle. The rider turns the pedals which rotate the front chainring (driver gear) with 48 teeth. A chain connects the cha...
Question 1 Report
Fig 22 shows the gear system on a bicycle. The rider turns the pedals which rotate the front chainring (driver gear) with 48 teeth. A chain connects the chainring to the rear sprocket (driven gear) which has 16 teeth. The rear sprocket is attached to the rear wheel.
(a) Calculate the gear ratio of this bicycle gear system. Show your working. [1]
(b) State whether this gear arrangement increases the speed or increases the torque at the rear wheel. [1]
(c) Explain your answer to part (b). [1]
Answer Details
(a) The gear ratio is calculated by dividing the number of teeth on the driver gear by the number of teeth on the driven gear:
\[ \text{Gear ratio} = \frac{\text{Teeth on driver}}{\text{Teeth on driven}} = \frac{48}{16} = 3 : 1 \]
This means the driver chainring turns once for every three turns of the rear sprocket. [1]
(b) This arrangement increases speed. [1]
(c) The driven gear (rear sprocket) has fewer teeth than the driver gear (front chainring). Because the chain links the two together, each full rotation of the 48-tooth chainring pulls enough chain to rotate the 16-tooth sprocket three complete turns. The rear wheel, which is fixed to the sprocket, therefore spins three times faster than the pedalling rate. However, this speed multiplication comes at a cost: the torque (turning force) at the rear wheel is reduced to one-third of the pedalling torque. This is a direct consequence of the conservation of energy in a gear system - when speed is multiplied, force is divided by the same ratio. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
