## Moving Heat Energy

Winter always reminds us of how important it is to have ways of moving heat energy from one place to another. We are considering how the complex heat transfer system is another evidence for God’s creative wisdom. Yesterday we looked at heat transfer by radiation. There are two more methods.

A second way of moving heat energy is by conduction. When you put a spoon into a hot cup of water the molecules that make up the spoon begin to vibrate faster as they absorb heat energy from the water. As one molecule gets energy, it bumps into the next molecule, and it also starts to vibrate. This happens down the length of the spoon, and eventually, the heat is conducted to your skin.

How fast heat conduction happens depends upon the size, mass, and density of the material in the object conducting the heat. Gases have poor conductivity because their molecules are far apart. A winter coat has lots of spaces between the fabric molecules filled with air. Fur has air spaces between the hairs and inside the hair strands themselves. Those low-density spaces insulate against heat transfer. You have heard the old story about never putting your tongue on a very cold metal object. The reason is that the water in your tongue conducts heat away to the metal surface which is very dense. The heat transfer process happens so fast that the water in your tongue freezes.

A third method of moving heat energy is by convection. Heating air or water is difficult by radiation alone or by conduction alone. The materials are transparent, so they absorb radiation poorly. Conductivity is slow and limited as to how far the heat can travel. What happens is that molecules change their density as they are heated or cooled. When heated, the gas or liquid becomes less dense it rises taking heat energy with it. As it cools, it sinks because it becomes denser. The motion mixes the hot and cold in the process we call convection.

The amazing ability of water to change its density as it is heated and cooled allows lakes to form ice on the surface rather than on the bottom. Water was designed to have its lowest density at 32 degrees Fahrenheit. It has a higher density both above and below that temperature. A very complex chemical property of water is designed to handle the heat energy by becoming more dense down to 32 degrees and then less dense as it freezes into ice. You can read more about this essential characteristic of water in THIS PREVIOUS POST and in our book Dandy Designs Volume 3, available HERE.

We take for granted the various methods of moving heat energy in and around us, but the complexities of this design are amazing. My physics students love to see how this allows us to exist on this planet.