Here's why:

* Conduction is the transfer of heat through direct contact between molecules. This is how heat travels through solids.

* Convection is the transfer of heat through the movement of the fluid itself. Warmer, less dense fluid rises, while cooler, denser fluid sinks, creating a circulation pattern.

* Radiation is the transfer of heat through electromagnetic waves. This is how the sun's heat reaches the Earth.

So, when you boil water on a stove, the heat from the stove is transferred to the pot by conduction. But the heat then spreads throughout the water by convection, creating the swirling patterns you see.