Just sayin...

Below I'm starting a collection of 'sayings' and my expectation of how they came about.

A watched pot never boils: If you heat with wood it is hard to get a pot to boil especially if the air temperature is cold. So putting a lid on it helps keep the heat in and helps bringing it to a boil. If you keep taking the lid off, you remove the heat insulation level and that prevents it from boiling.

It is faster to freeze hot water than cold. If you freeze your pot by putting it in snow (think before the days of 'freezers') the snow acts as an insulating blanket, so cold water takes a long time to freeze. But if you put hot water in it, the pot sinks through the snow to make a solid connection with the soil (it melts the snow and the melted snow will help make an even better connection between the ground and the pot) and now the pot has it's heat sucked away much faster than the cold pot. As a result, it is faster to freeze hot water than cold. Note that in a modern freezer, or when you are able to get a good connection with the ground (remember that melted snow helps give a good connection), cold water freezes faster than hot water.

Another reason I've considered: Water needs to lose 80 calories of energy to change 1 gram of pure water from 0 liquid to 0 frozen. It also needs to lose 80 calories of energy to go from 80C down to 0C (the freezing point). That means the act of freezing and thawing is VERY energy intensive.

So what if you start with 1 litre (or 1 gallon - the exact amount doesn't matter) of water at 90C and 1 litre at 15C. In RELATIVE terms it is going to take 95 calories of energy for the cold pot and 175 calories of energy for the hot pot.

But now, lets assume that because of the outside temperature, the pot of 90C water loses 50% of it's volume through evaporation on the way to 0 and lets assume for simple numbers the cold pot loses none. The cold pot still needs to shed 95 calories of energy, but the hot pot only needs to shed 40 (the half that has to be frozen) plus 45 (the energy to cool down half the liquid.) While these exact numbers are not going to be correct - notice that this means the hot pot only needs 85 calories to freeze - but there won't be as much frozen of course. Various more careful values based on this may be the reason people have concluded that hot water (sometimes) freezes faster than cold water.

Update: I have read more about the hot/cold water freezing and there are other specific cases. The funny thing some 'scientists' (with a bunch of official looking letters behind their names) make fun of the answer I initially gave, saying 'of course that is not a normal case, no one goes around putting pots on a layer of frost'. What I think THEY are forgetting is: This is an old phrase - much older than freezers. So in their arrogance (yes I have my own arrogance!) they conclude that that reason is not a realistic one, when in fact, all the cases THEY give only will make a huge difference in modern environments. Ah the foolishness of modern scientists - blinded by their 'one factor only' method of thinking.