The buoyancy of the dumplings at the beginning is less than gravity, because after heating, the air inside the dumplings expands by heat, which increases the volume of the dumplings. According to the formula for calculating buoyancy, the volume increases and the buoyant force increases, which is greater than the force of gravity and then floats.

Expanded information:

The concept of buoyancy:

An object immersed in a liquid or gas is buoyed by the vertical force of the liquid or gas. object is held vertically upwards by the liquid or gas is called buoyancy.

Explanation

Buoyancy:

An object immersed in a liquid (or gas) is held upward by the force of the liquid (or gas).

Direction of buoyancy: opposite to the direction of gravity, vertically upward.

Cause of buoyancy: an object immersed in a liquid or gas is subjected to the difference between the upward and downward pressures of the liquid or gas on the object.

Summary

When the top interface of a floating body is not in contact with the liquid, only the upward pressure acting on the bottom interface produces buoyancy. As for an object located on the bottom surface of a container, there is not much of this phenomenon, because as long as there is a very thin film of liquid in between, it can transfer pressure, and there is an upward pressure on the bottom surface, and there is a pressure difference between the top and bottom surfaces of the object, and the object is buoyant.