When you pedal a bicycle, you are using the force generated by your leg muscles to turn the bicycle’s pedals, which in turn rotate the rear wheel. This rotational force, or torque, is transferred from the pedals to the rear wheel through the bicycle’s drivetrain (chain, gears, etc.).

The rotation of the rear wheel creates a frictional force between the tire and the ground. This frictional force propels the bicycle forward. Without pedaling, the bicycle would not have the necessary rotational force to overcome the forces opposing its motion, such as air resistance and rolling resistance.

So in summary, we need to pedal a bicycle to generate the torque required to rotate the rear wheel and create the forward propulsive force that moves the bicycle. The pedaling action is the essential mechanism that enables a bicycle to move forward under the rider’s own power.