I was sitting down yesterday and saw my phone vibrate on a side, and it moved about a centimetre per vibration. I wondered why it moves, and thought perhaps that the side it was on had a slight slope, because it tended to move in the same direction every time. So I then though, what if the side was perfectly flat? Well, then I considered the fact that the phone's centre of mass would make it move in a biased direction (is this correct?).
So I then thought, what if the phone's centre of mass was in the exact centre, and the slop was perfectly flat?
Would the phone still move?
And if so, what factor would make it move in a particular direction?