April 27, 2011

Physics Professor Discovers Secret to Bikes’ Stability

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Cornell researchers have found that commonly-accepted explanations for a bicycle’s self-stability are false, according to a study published last week in Science, an academic journal.

The science behind a bicycle’s self-stability has eluded researchers since its invention in the late 1800s, said Prof. Andy Ruina, mechanical and aerospace engineering, who co-authored the study.

“A bicycle’s not all that simple. The mechanics of three-dimensional objects are complicated,” he said. “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.”

In coming to its conclusions, the bicycle research team had worked to disprove previously-accepted theories concerning self-stability, Ruina said. Earlier scientists in the field have argued that necessary factors included “gyroscopic motion” — the spinning of the front wheel — and a design feature called “trail,” the forward placement of the steering axis ahead of the front wheel’s contact point with the ground.

“Jim Papadopoulos, back in the 1980s when he was at Cornell, his first thing was to get some good equations for the bicycle, and that was actually a lot of work. Lots of people have tried and they’ve mostly been wrong,” Ruina said.

The final step was to actually build a bicycle without using either gyroscopic motion or trail, Ruina said.

Ruina’s colleagues, Arend Schwab and Jodi Kooijman, a student at Delft University of Technology in the Netherlands, accomplished this task, he said.

The bike they designed — called the two-mass-skate bicycle — had no gyroscopic effect and no trail. Ruina said, however, that it was necessary to include handle bars that turn in the directions of the fall if the bicycle were knocked over.

Now that the team has broken new ground concerning self-stability, Ruina said they plan to continue their research with bicycles.

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

Original Author: Christa Nianiatus