Conduction

Have you ever wondered why people like staying inside during the winter? You're probably laughing at that question, given how obvious the answer seems. Yes, it's warmer inside during the winter, usually. However, why is that? Well, here's another obvious answer: its because your home's walls insulate heat well so the cold from outside doesn't make it into your house.


The form of heat transfer that deals with this is known as conduct. When you touch a metal, it feels cold because metals conduct heat well. Thus, when you're touching a metal, the metal atoms are basically absorbing the kinetic energy of your hand's molecules, so it "absorbs" the heat from your hand such that the temperature of your hand decreases and the temperature of the computer increases.

So this diagram represents the conducting material between two systems of different temperatures. The rate of heat transfer through a conducting material is given by:

So, k is a quantity known as the thermal conductivity of a substance. It's characteristic of every substance, kind of like coefficients of friction or specific heat capacities. The units for k are usually Joules/(second meters degrees Celsius).


A is the surface area of contact for the material. This makes sense because if the surface area is higher for a "wall", then more particles can conduct the heat.


The quantity T2-T1 is the difference in temperature between the two systems that the conducting material is between. Heat always transfers from hot to cold so the sign of this quantity depends on your perspective.


The quantity d is the thickness of the conducting material. If the thickness is high, then the conduction rate will be slower because it'll take longer for heat to transfer through.


Below is a table of thermal conductivities for common substances:

Citations/Attributions