Convection is the heat transfer due to the motion of a fluid, such as a gas or liquid, that carries heat energy away from a heat source. Conduction instead occurs between materials in contact with each other without any movement between them. Convection is more efficient than conduction for heat transfer because the fluid that absorbs heat in convection moves away from the heat source, being replaced by cooler fluid.
Convection is seen when the heated water on the bottom of a pot expands, becomes less dense and rises, being replaced by cooler water. This circulation of fluid is known as a convection cell and is the reason why warm air rises and cool air falls over a hot surface.
Conduction is responsible for the heating of the pot by its direct contact with the heating element of the stove. Its cause is the movement of the molecules in a material due to its internal energy, known as heat. These fast-moving particles collide with the slower ones that they interact with, transferring energy to the slower molecules. This phenomena also happens with convection, as energy is initially transferred from an object to the moving fluid through conduction. However, the added motion of the fluid to take the heat away from its source differentiates convection from conduction.