Question

Water is boiling in a clear pot, as shown in the picture.

A clear pot full of water sits over gas burner. The water has large bubbles rising in the water.
Which takes place as water cycles from the bottom of the pot toward the top?

Thermal energy is transferred.
Water molecules gain kinetic energy.

Answer 1

Both. The burner heats the water at the bottom (thermal energy is transferred into the fluid), so those molecules gain kinetic energy (move faster and expand), become less dense and rise — carrying heat upward by convection.