Teacher Toolbox - The Purpose of this Page
This Apply section will help students understand how a mechanical advantage is applied in the real world by analyzing the torque and speed of bicycles. Different bicycle gears will be analyzed in relation to torque and speed.
Pedal Faster or Pedal Stronger!
When riding a bicycle, maintaining a certain pedaling speed (also called cadence) regardless of hills or flat road is important. To transfer power from the pedal to the wheels involves the usage of gears.
There are two places that gears exist on a bicycle. The first is connected to the pedal, called the chainring. The second place is connected to the back tire, called the rear cog or sprocket. The gears are connected by a chain. The chain transfers the power applied at the pedal to the wheels and a mechanical advantage is created based on the size of gears connected to the pedals (front cassette) and wheels (rear cassette).
There are different bikes with varying numbers of gears called chainrings and sprockets. A single gear bike remains at a fixed mechanical advantage - the gears that are on a single gear bike will not change regardless if the person is pedaling on a flat road or a hill. This means the person pedaling has to put all the strain on their legs in order to climb hills or ride much faster.
A multi-geared bike allows the person pedaling to maintain the same pedaling speed to adjust their mechanical advantage to reach different outcomes. This enables the rider to climb hills or travel faster without changing their pedaling speed.
A bicycle with multiple gears gives many options to use mechanical advantage to their personal advantage. A bicycle at a stand-still would want to use a gear combination suited for more torque (turning power) in order to accelerate from a stop or to climb a large hill. A mechanical advantage for torque (more turning power) is achieved when a smaller gear drives a larger gear. In the context of a bicycle, this happens when the smallest front chainring size is paired with the largest rear cog or sprocket. However, a bicycle geared for torque will not be able to move very quickly.
On the other hand, a bicycle that is already moving and wants to reach a fast speed needs to use a gear combination suited for more speed (rate of motion) in order to achieve a high speed without having to pedal hundreds of times per minute. A mechanical advantage for speed is achieved when a larger gear drives a smaller gear. In the context of a bicycle, this happens when the largest front chainring size is paired with the smallest rear cog or sprocket.
Having a mechanical advantage when biking allows riders to get the most out of the amount of energy they exert. A mechanical advantage can be applied in many different situations and become desirable when designing a robot for a competition.