Science Assessment

Which of the following correctly describes energy transfer by convection in a liquid that is heated from below?

1. As the temperature of the liquid increases, the atoms that make up the molecules of the liquid rub faster against each other. The rubbing creates energy that spreads throughout the liquid.
2. As the temperature of the liquid increases, heat molecules are transferred from the heat source to the liquid. These heat molecules travel upward between the molecules that make up the liquid, transferring energy as they move.
3. The molecules of the liquid closest to the heat source spread apart and create a less dense region of liquid. An upward force on the less dense region then pushes the liquid and its energy upward.
4. The molecules of the liquid closest to the heat source collide with molecules farther away from the heat source. Energy is transferred through the liquid by the force of these collisions, but the molecules themselves do not move from place to place until the liquid boils.