material of a container that holds water vs rate it freezes

[sk_ik5]

I have to teach my kids about the following, by experimenting and facts. I know that water in steel container will freeze faster than glass . But how to explain through science? can anyone help?

Is there a relationship between the material of a container that holds water and the rate at which that water freezes?


Sherry

[deleted-71631]

Sherry,
You have a great opportunity to show your students, with hands-on experiments, why some materials conduct heat (or cold) better than other materials.
The "thermal conductivity" coefficient k describes the thermal conduction properties of different materials. A concise description can be found at

http://en.wikipedia.org/wiki/Thermal_conductivity

and, in addition, there are numerous posts on Science Buddies with discussions and experiments on thermal conductivity and insulators.
Do a 'search' on the Science Buddies site and you'll find lots.

In general, the lower the thermal conductivity value for a given material, the better that material behaves as an insulator.
From the wikipedia site, we find:

thermal conductivity for glass: 1.1
" " " stainless steel: 12.1 to 45.0
So these values support the hypothesis that glass will be a better insulator for the water, slowing down the freezing compared to a steel container.

In your experiment, it's very likely that the steel container will have thinner walls compared to the glass - the thicker glass wall will also slow down the cooling effect. So there are two effects that you can point out for the better insulation properties of a glass container, compared to a steel container, that will insulate the contents and slow down the water freezing effect: the much lower thermal conductivity and the thicker glass walls.

Good luck and have fun!

Peter Young

[kgudger]

One more thing - to make this a better experiment, make sure that these containers completely enclose the water. If both containers have open tops, then freezing will occur from the top at the same rate for both containers. You might not see a lot of difference in freezing rates in this case.

Keith