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Mystery of the riderless bike thickens

By James Dacey

The riderless bike is a fairly well known quirk of mechanics. As the name suggests, it refers to the fact that regular bicycles can keep going by themselves for long distances without toppling over. Indeed, the surreal image of a riderless bike inspired this brilliant scene in Jour de FĂȘte, a black and white French comedy from 1949.

But a new bike created by researchers in the US is and the Netherlands has cast doubt on our understanding of what causes this effect.

The phenomenon of bicycle self stability was first described analytically in 1897 by French mathematician Emmanuel Carvallo, and since that time many other scientists have contributed their two pennies worth.

While it quickly became clear that the mechanics behind the effect are not as simple as one might think, most researchers agree that the stability is due to two features of mechanics. Firstly, there is gyroscopic motion, which causes the front wheel to correct itself like a spinning top. Then secondly, there is the “trail” or “caster” effect, which also explains why the front wheel of a shopping trolley automatically turns to follow the pivot.

A team including Andy Ruina at Cornell University has created a bike that self-balances without relying on these forces – the first of its kind. The researchers published their findings in this week’s edition of Science.

Ruina told the Science podcast that the balancing must still be related to a mechanical effect that couples the forces involved in bike-leaning to its steering. While the bike currently looks more like a child’s scooter, Ruina sees no reason why it could not be rearranged to appear more like a familiar motorcycle or bike.

To see the bike in action, follow this link.

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