Molecular Activity

• Heat transfer is a process of thermal energy movement. It is governed by scientific laws that dictate, in summary, that such energy will also seek equilibrium, and move from substances of high energy to substances of low energy, trying to make their thermal energy equal. Thermal energy is most commonly measured by temperature, which shows us that energy flows in an attempt to make substances the same temperature. Heat from hot objects will flow to cold objects in an attempt to achieve balance, known as thermodynamic equilibrium. Cold, on the other hand, is simply a condition of low thermal energy from the objects surrounding it, and cannot "move" in the same way as heat.
  
  On a molecular level, thermal energy shows as the kinetic energy of molecules. Hot molecules vibrate with energy, bouncing off each other more easily and moving quickly through space. This is because their atoms have a large amount of electrons, a key component of kinetic energy. In hot materials, where many electrons are present and moving around, these atoms have electrons that jump up to higher levels and at times jump away from the atom, seeking another atom to join. Properly controlled, these charged electron streams can become electrical current, but in most naturally heated substances electrons are usually contained, busy jumping up levels and making their molecules vibrate at a quicker rate.
  
  

Heat Movement

• Thermal energy is always moving. No matter what substance is heated, there is always another place for the heat to move, unless all available substances are the same temperature and equilibrium is reached. This is particularly true on earth, where thermal energy is concentrated in specific places, although some substances manage to hold onto their heat longer than others. Substances of similar temperatures will exchange heat more sluggishly, while substances with a large temperature difference, such as the air and fire, will exchange heat very quickly. Some substances can hold onto heat longer than others. Water, for instance, holds heat for longer periods than metal.
  
  

Three Types of Thermal Transfer

• The process that thermal heat uses to move through a substance and between one substance and another is essentially the same, but scientists have divided heat transfer into three different categories based on how the movement of the heat. The first type of heat transfer is conduction, in which the molecules transfer thermal energy by direct contact. They collide with the molecules of a less active substance, and the energy flows from the hot molecule to the cooler molecule. When you touch a heated surface like a hot rock, conduction is the warmth you feel.
  
  Convection is another type of heat transfer involved fluid expansion. Heated fluids generally expand, transferring their heat as they move. The final type of heat transfer is radiation, through which heat is passed on by light photons. All objects produce some type of heat radiation, even if it is a very small amount. If the object and its surroundings are at equilibrium, then they are probably exchanging the same amount of radiation with each other.