It's rare that bicycles feature in the Cornell Chronicle, but today there is an article about interesting research by Cornell prof Andy Ruina on what prevents bikes from falling over. The main finding is that conventional theories of self-stability -- the gyroscopic effect of the spinning wheels and trail of the front wheel -- are not the main factors in keeping a bike stable. Ruina and his collaborators have constructed a bike (well, it doesn't look exactly like a bike) that has no gyroscopic effect and no trail -- but still stays upright on its own. Fascinating stuff with potential practical implications for bicycle design.
There's also a video explaining the research, and here's a the pre-print of the article which will be published in Science.