What do you feel in summer, hot or extremely hot? Whatever your answer, whether it is hot or cold, it refers to the same measure. When a substance is called hot, it means the level of heat is high. While if it is called cold, the level of heat is low. How to measure this heat level? Good thing that temperature scales were invented by scientists in the past. Name it Fahrenheit unit, it was named after Daniel Gabriel Fahrenheit who proposes this standard. It was based as melting point of brine as 0 oF, melting point of water as 32 oF and boiling point of water as 212 oF.
Now, when you touch hot surface, why do you feel hot at your skin surface? That is heat transfer. Area that have high level of heat will transfer to area which is have low level of heat. Some define heat transfer as energy movement from one part to another part due to temperature differences.
Based on that definition, heat transfer basically depends on temperature difference and the type of materials. Another factor that is affect heat transfer is method of heat transfer. There are three methods of heat transfer:
In conduction, heat is transferred from particle to particle inside one medium or several connected mediums without any movement from its particle. This heat transfer method mostly assumed to occur in solid medium. Solid medium has tight atomic arrangement that hinder the movement of its particle even at atomic level.
In convection, heat is transferred along with the movement of its medium. This method is observed in gaseous and liquid phase. Simple example of this method is flowing hot air from car radiator.
In radiation, heat is transferred without any medium. Or, the medium can be present, but the medium has no impact to the transfer process. The heat is transferred as electromagnetic wave. Heat from the sun is mostly transferred through this method.