Moving Forward by Pushing Back
We have seen how the drivetrain transforms pedaling into rear tire force which you might have noticed pushes in the backwards direction. So what is moving the cycle ultimately forward?
Newton’s Third Law in Action
We are actually one step from our final result. Newton’s Third Law is often considered different from the first two, but here it shines, and explains how the road is actually the source for what is pushing the cycle forward.
Let’s first understand the process of jumping. You think you are jumping up, but what you are really doing is pushing down on the surface in the opposite direction to up. By Newton’s Third Law of equal and opposite reactions, the floor is pushing back against your feet and exerting an upward force. Therefore, it is the floor pushing you upward.
The Road as a Moving Force
It is the same with cycling. The drivetrain turns the rear wheel clockwise thereby exerting a backward force to the road. Then by Newton’s Third Law, the road exerts an equal and opposite force in the forward direction which is what moves the cycle forward.
So we have our answer. The force moving the cycle in the forward direction is coming from the road. This actually makes it clear that we are riding on the road.
Next Topic: Cyclist Modeling