Scientists in Paris have figured out what causes rolling suitcases to wobble then overturn. Their counterintuitive solution to the problem: speed up.
How it happens: Physicists studied suitcase instability by creating a model of a two-wheeled suitcase rolling on a treadmill. They found that a suitcase unsurprisingly begins to rock when it hits a small bump or something knocks into it. When one wheel is lifted off the ground, the tilted suitcase shifts to realign the wheels but when the wheel hits the ground again, the other one lifts and the energy from movement is transferred, rocking the suitcase the other direction. The motion continues or the suitcase falls over so long as the energy from rocking is greater than the dampening that occurs when the wheel touches the ground again.