Why is a good conductor of energy also a good conductor of heat?

Question

Why is a good conductor of energy also a good conductor of heat?

Answer 1

Heat IS energy.  Typically, the same  features that make something (like metal) a good conductor of electrical energy makes it a good conductor of heat energy as well.

Answer 2

Copper is one of the best heat conductors. They are often used as heat sinks for CPU fans and other areas where a lot of heat needs to be absorbed/radiated.

Answer 3

There are two ways heat gets conducted.  

One is through phonons (no, not photons).  Phonons are vibrations of material.  Materials that are very stiff and have good bonds between neighboring atoms allow phonons to pass from atom to atom very easily (as in crystals).  

The other way heat is transfered is via electrons.  In some materials, electrons are relatively free to hop from atom to atom.  When this is the case, when an electron gets hot (starts to move fast) at one end of the material, it can move to the other end of the material and, thus, transfer the heat energy along the material.  Metals are the best example of a material where the electrons are free to move, since the valence electrons in a metal form an "electron sea".

Generally speaking, materials that are good phonon conductors are very bad electron conductors, and vice-versa.  However, both are good heat conductors.

Now, if you think of how electricity flows through a material, a voltage on one end of the material attracts electrons to it and the electrons form an electrical current as they rush toward the voltage.  The easier it is for electrons to move, the more current forms (if electrons can't move from atom to atom, almost no current will form at all).   The more current, the better the electrical conductor.  So again, metals make great electrical conductors, since the electrons are free to move.

Therefore, metals are good at both conducting electricity and heat because the electrons are free to move inside the metal.  However, good phonon conductors (like sapphire) are only good at conducting heat and NOT electricity.  Therefore, good electrical conductors are also good heat conductors, but good heat conductors are NOT NECESSARILY good electrical conductors.