Most recent answer: 02/09/2013
- Sunny Singh (age 18)
Sasaram, Bihar, India
The method behind instantly freezing a container filled with water is actually rather simple. Water with particles filtered out (e.g. reverse-osmosis water) left in a freezer undisturbed will remain a liquid even when the temperature is a couple of degrees lower than the freezing point. We say that it is supercooled which means that is in a metastable state where the slightest disturbance (from shaking the bottle to dropping a bead in it) will instantly cause it to partially freeze. However, this works much better for filtered water than for tap water as the impurities in tap water can serve as nucleation sites for crystallization. So to do this instant freeze trick you need pure water. To know when the water is cold enough, you can put a bottle of tap water next to a bottle of filtered water in your freezer. When the tap water is frozen, you can take out the filtered water bottle and shake it. You should then see the water instantly freeze into slush.
If you are interested in how supercooling works, see this answer to a similar question:
(published on 02/09/2013)