New research uncovers why a bicycle stays stable when moving
For over a century scientists have been puzzling over the physics of the trusty bicycle, and new findings from an international team of researchers have thrown new light on this age-old question. The team, made up researchers from the Delft University of Technology (TU Delft) in the Netherlands and Cornell University in the United States, focused on finding out why a bicycle remains stable above a certain speed. When you add speed to a bicycle it becomes stable on its own and you could push it sideways without it falling over. It was previously thought that this stability was related to two factors. First, the rotating wheels of the bicycle were supposed to provide stability through gyroscopic effects, and second, it was thought that the 'trail' played an important part - the distance by which the contact point of the front wheel trails behind the steering axis. These new findings, published in the journal Science, cast aside this old theory. 'We have known for years that the generally accepted explanation for the stability of the bicycle was too simple,' says researcher Dr Arend Schwab of the 3mE faculty at TU Delft. 'Gyroscopic effects and trail do help, but are not essential for stability.' Dr Schwab and his team used a mathematical model with around 25 physical parameters which they had developed for a previous study. This model can predict very accurately whether, and at what speeds, a particular design of bicycle would be stable. Building on this work, the team designed and constructed a bicycle with which to show in an experiment that both gyroscopic effects and trail are not necessary for a bicycle to remain stable by itself above a certain speed. 'In our publication in Science we have now shown not only theoretically but also by means of experiment that our insights are correct,' says Dr Schwab. The so-called 'Two Mass Skate' bicycle they developed has small and counter-rotating wheels, meaning there is no gyroscopic effect to speak of, and a small negative trail. The point of contact of the front wheel is slightly beyond the steering axis, and yet the bicycle remains stable. 'It was not easy,' explains PhD student Jodi Kooijman, who carried out much of the experimental work. 'The first prototype did not work, and we had almost given up hope after a number of iteration attempts, when we suddenly found ourselves able to show the stability. You have to deal with the ground surface, for example, which has to have exactly the right roughness and stiffness.' Having proved their theory through a series of experiments, Dr Schwab explains the theoretical implications of the study. 'We have demonstrated that the mass distribution is also important for stability, especially the location of the centre of mass of the bicycle's steering mechanism.' In other words, for a bicycle to be stable, the steering mechanism has to be unstable; if the bike falls, the steering should fall even more quickly. These findings also have implications for bicycle manufacturers. Although the design of the bicycle has changed little since the end of the nineteenth century, these new findings could help develop new modifications for different types of folding bicycles and cargo bicycles.For more information, please visit:TU Delft:http://home.tudelft.nl/en/
Countries
Netherlands, United States