1. The problem statement, all variables and given/known data You are riding in a train and have just opened a bottle of beer. Prove that for your bottle to be as stable as possible on the table (which is shaking), you should drink sufficient beer such that the surface of the beer coincides with the centre of gravity of the partially filled bottle. You may wish to begin by assuming that the bottle is of constant cross-section. The condition above for maximum stability is actually independent of the shape of the bottle. Give a logical argument for why this is the case. 2. Relevant equations 3. The attempt at a solution I am not quite sure. I would have thought that to be the most stable the centre of gravity for the drink and the bottle should be in the same place - it appears I am mistaken. Any ideas?