I don’t know bupkis about physics but they say that if you create a wheel that contains another rapidly spinning wheel, the gyro effect will keep the wheel upright. That’s the idea behind Gyrobike. Ars Technica spoke with CEO Daniella Reichstetter:

“Our challenge was not only to develop a front bike wheel with a disk that could do this, but also to find a way to get the disk to spin fast enough to create enough force (gyroscopic precession) that would help stabilize the bike at a low speed so that a rider could benefit from the stabilizing effect,” she told Ars.

They balanced safety, form, and function… not to mention trying to make the product interesting for children. “We fully enclosed the disk to keep small fingers safe. We enclosed rechargeable batteries and motorized the disk. Ultimately, we created a ‘cool’ design that allows kids (and adults) to see the ‘magic’ disk in action.”

The wheel includes a built-in rechargeable battery, and can be set to three stability settings, or be turned off altogether. As the young bikers learn how to ride, the power can be turned down accordingly until they’re finally biking on their own. […]

Adult bikes with the technology, which for now will only be sold through the website, could be good for senior citizens who would like a safe way to continue biking, and Reichstetter also said there is much interest in the original unicycle design. As for what configurations we’ll see in the next few years, she would only say that they’re working on a number of products.

The child version should be available for Christmas. Adult and unicycle versions later in 2010.