Most travelers pulling suitcases soon discover that every so many yards you've got to stop, straighten out and start again. Annoying, but what can you do?
Well, it turns out that our troubles have not gone unnoticed, and a professor at the Sorbonne and his graduate students have now published a paper in Britain's prestigious Proceedings of the Royal Society A: Mathematical and Physical Sciences. The paper explains that it's not bad construction, or worn wheels, or uneven pulling; they're all off the hook. The villain is physics!
Sylvain Courrech du Pont, a researcher at the Complex Materials and Systems Laboratory of Paris-Diderot University explained to AFP that "The tendency of a two-wheeled suitcase to oscillate from one wheel to another is due to an inherent mechanical instability," which comes from the intersection of types of motion, rotational and translational. "It may seem paradoxical, but it is precisely because the suitcase is designed to roll in a straight line that it moves sideways."
By the way, he said, if you run faster instead of stopping, you'll solve the problem another way.
For a fuller explanation, appearing in Japan Today, click HERE