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Engineers disprove commonly held beliefs about the physics of bicycles

Engineers disprove commonly held beliefs about the physics of bicycles

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Next time you ride your bike, you may want to take a moment to marvel at the complexity of the physics behind it. According to a recently published study, commonly-accepted explanations about the self-stability of bikes are actually false.

Cornell mechanical and aerospace engineering professor Andy Ruina asserts that the science behind a bike's self-stability has been a mystery for well over a century. "A bicycle's not all that simple," Ruina affimed. "The mechanics of three-dimensional objects are complicated. In some sense, it's been well understood since the mid-1900s in that people can write the equations, but in terms of having some intuitive understanding of it, nobody ever has."

The researchers first disproved formerly held beliefs about what contributed to self-stability, including gyroscopic motion and a design feature called "trail," which places the steering axis ahead of the front wheel's contact point with the ground. The team of scientists endeavored to build a bike that used neither of those features - and they were ultimately successful.

Although the resulting bike, dubbed the two-mass-skate bicycle, lacks gyroscopic motion and trail, it does have handle bars that turn in the direction of the fall if the bike tips over. Ruina contends that while the research could seem trivial, it is indicative of bigger questions scientists still have no answers for.

"Very little is known about how people do anything," he said. "We don't know how people walk; we don't know how people hold still; we don't know how people hold things. So one of the things to try to figure out is how people ride a bicycle and what about the bicycle makes it easy or hard to ride."

 

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