Heat is energy created by the molecular movement of atoms. All matter with a temperature above absolute zero has heat. The transfer of heat occurs by three different mechanisms: conduction, convection, and radiation.
Conduction is heat transfer through solids. Heat travels from regions of higher temperature to regions of lower temperature. The rate of heat transfer depends on the thermal conductivity of the material and the difference in temperature along the path (temperature gradient).
Convection transfers heat through moving fluids. Fluids carry energy from a hot surface (or cold) by absorbing heat as the molecules in the fluid come in contact with the surface. The rate of heat transfer depends on the temperature difference between the fluid and the surface. The rate is also affected by other properties such as the orientation of the surface, the type of fluid, and the flow velocity.
Radiation transmits energy through electromagnetic waves. All objects above absolute zero emit thermal radiation. Hotter objects emit much more radiation than cooler ones, with the amount of emission proportional to the object’s temperature to the fourth power. The color of an object also affects its radiation (and absorption). Theoretically, a blackbody in thermal equilibrium has an emissivity of 1, an indication that this color will emit the maximum amount of energy for a given temperature. It is important to note that although all objects emit heat energy through radiation, the temperature change of an object depends not only on the amount emitted, but also on the amount absorbed. The temperature change of an object depends on the net effect of all energy emitted and absorbed through all forms of heat transfer.
