When the glutinous rice balls float, it means that the glutinous rice balls are cooked, because the density of raw glutinous rice balls is relatively high, and the density is higher than that of water. When they are put into water, gravity will dry out and buoyancy will sink to the bottom of the pot. After jiaozi enters the pot, with the increase of water temperature, the stuffing and skin of jiaozi will gradually expand after being saturated with hot water, and the volume will increase, the volume of boiled water will increase, and the buoyancy will increase. When the jiaozi is fully inflated, the buoyancy is greater than gravity, and the jiaozi will float. So it seems that the cooked jiaozi is bigger than the raw one.

Tangyuan is in boiling hot water. Cook the skin of the dumplings first, and then cook the stuffing of the dumplings. At this time, the air wrapped in jiaozi also became hot. When heated, the air will expand and swell jiaozi's stomach. Jiaozi's stomach swelled and became lighter than water, so jiaozi floated from the bottom of the pot to the surface.