Why suitcases rock and fall over decoded

Scientists have solved the puzzle behind why suitcases rock and fall over, finding that speeding up rather than slowing down can solve the problem.
It is a common experience that a two-wheeled suitcase rocks alarmingly from side-to-side and threatens to overturn when dashing for a train or plane.
Now, scientists from Universite Paris-Diderot in France have investigated this conundrum of everyday physics.
They found that speeding up rather than slowing down can solve the problem and that people can also pivot the handle of the suitcase as close to the ground as possible.
Researchers studied a model suitcase on a treadmill to see what goes wrong when a suitcase rocks out of control at high speed.

They developed equations to explain why two-wheeled trolleys have a tendency to rock from one wheel to the other.

In case of unstable bags, after having gone over a bump, for example, they found that luggage rocks from side-to-side until it falls over, or it reaches a regular side-to-side swing, 'BBC News' reported.
If a regular side-to-side swing develops, going faster results in smaller swings, the researchers said.
"Thus, one should accelerate rather than decelerate to attenuate the amplitude of oscillations," they said.
"The suitcase is a fun way to tackle the problem but the study would be the same for any trolley with two wheels or blades," said Sylvain Courrech du Pont, of Universite Paris- Diderot, who led the study published in the journal Royal Society Proceedings A.