Let us assume we have a big ice cube on a rigid table(on Earth).
After a while the ice cube will melt, if we are on Earth then the ice will get converted into water and spread on the table.
Therefore the center of mass of the ice cube will be a little lower. What my understanding is that , it will get lower due to bombardment of air molecules.
But if we use light instead of air to heat it what should be the reason for the vertical displacement of center of mass?