This subunit analyzes the transfer of thermal energy between regions of matter due to a temperature gradient. Conduction characterizes the heat flows through the region of matter itself, as opposed to requiring bulk motion of the matter as in convection. Conduction takes place in all forms of matter, viz. solids, liquids, and gases but does not require any bulk motion of matter. However it mainly characterizes heat transfer in solids, since in liquids and gases convection is the main process of heat transfer.