Quote:
Originally Posted by mdf
Actually, cars do hold heat for quite a while. I've spent a whole day skiing when it was 14 F when I left the car and 11 F when I got back, and the water bottles I left in the back seat were not frozen. They were chilly, but not frozen.

With my limited knowledge of thermodynamics, a litre of water will take approximately 29 mins to freeze when it starts at 25°C. Here's an equation for that:
Energy needed to freeze is:
E = cm∆T = 4.17 Jg1 K1 x 1000g x 25°C = 104250 J
60 J per second so \frac{104250}{60} = 1737.5 \ seconds
1737.5 seconds is about 29 minutes.
So, unsure of what the water was stored in, the volume of the liquid, the area of the liquid, the exact substance of the liquid, any median that covers the liquid (e.g. plastic water bottle), or the fact the fluids are complicated and doubly so for water.
Or we could use Newton's Law of Cooling to try to determine the freezing point:
Freezer Temperature = Tf
Water temperature at start = Ts
Time taken to reach the freezing point,
t =\frac{1}{K}~~ ln~ \frac{ T_s  T_f}{0  T_f}~~~
working in deg C (ie: final temp = 0C).
K is a constant that is dependant on air flow profiles and container geometry, so it is essentially unknown until you determine it experimentally for a given geometry and set of conditions.
The second part of the solution is the crystallization time (which will be much smaller than the time till crystallization, so may be neglected), and this too is extremely sensitive to conditions such as water purity, vibration levels and container geometry, so there's no way to tell this number theoretically.
Just too many factors to consider in your deeply scientific study on how cars retain heat.