Section 4: Matter and Energy
Temperature, Heat, and Forms of Heat Transfer

Substances with a high conductivity heat rapidly, transfer their heat rapidly, and are said to be good conductors. Most metals fall into this category, but there is a wide range of conductivity among them. A bimetallic strip comprises two strips of different metals (such as copper and aluminum) joined together, and is often used to demonstrate the different conductivity of the strips. Copper is a good conductor and heats up and expands quickly, whereas aluminum is a relatively poor conductor and slower to heat and expand. Their different expansion rates cause the metal strip to bend as it is heated.

Substances for which conductivity is low, such as asbestos, wood, and air, are poor conductors of heat and are therefore good insulators. Materials with low conductivity do not transfer their heat rapidly. This is the secret behind walking on hot coals bare-footed. The coals may be 400˚ C but they conduct the heat relatively slowly to the bare-footed walker. Ask the walker to stand still for a few seconds and see if their “mind-over-matter” trick still works!

If a substance is a good conductor then it has a low specific heat. It will require very little heat energy to heat the substance. This means that the heat will be conducted rapidly, and so it will have a high conductivity due to its low specific heat. Water has one of the highest specific heats of all substances. It take an enormous amount of heat energy to raise the temperature of 1 gram of water just 1˚ C (1.0 calories / gram / C˚ compared to alcohol 0.58, aluminum 0.21, air 0.2, copper 0.093, gold 0.03).