The Physics of Freezing and Freeze Protection

Recently, there have been a lot of questions from those living in moderate climates about using automatic freeze protection or running pumps to prevent freezing and what a pool owner should do when temperatures drop so I thought it might be useful to have a thread which dealt with the issue from both a practical and theoretical point of view.

But first a few thoughts about using pumps to prevent freezing. Running the pumps is not fool proof and power outages can obviously be a problem...

The Physics of Freezing and Freeze Protection