Bicycles

Broadly defined, a bicycle is any two-wheeled, singletrack vehicle wholly propelled and guided by human power. Most are powered by the feet using pedals attached to rotating cranks, and they are guided by a transverse handlebar, but numerous alternatives exist and are not uncommon. The bicycle is unique in that it cannot be maintained upright or steered unless it is moving. Its physics are not well understood, and no fully successful automated bicycle has been developed. It was long thought the gyroscopic effect of the wheels was the bicycle's secret, but this was disproved by David Jones in 1970. It is now believed that as many as six separate forces contribute to the stability and responsiveness of a bicycle. Worldwide, between three and six times ...