# Why does ice expand?

**URL:** <https://boards.straightdope.com/t/why-does-ice-expand/80942>\
**Category:** Factual Questions\
**Created:** [September 11, 2001, 10:23pm UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942 "2001-09-11T22:23:17Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Mac](https://avatars.discourse-cdn.com/v4/letter/m/cc9497/32.png) [@Mac](https://boards.straightdope.com/u/Mac)\
**Post date:** [September 11, 2001, 10:23pm UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942/1 "2001-09-11T22:23:17Z")

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When you heat up water it expands and turns to steam. When you freeze water it also expands. Why does ice expand?

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**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\
**Post date:** [September 11, 2001, 11:04pm UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942/2 "2001-09-11T23:04:35Z")

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IIRC, it expands because water has polar molecules. That is, one side has a slight positive charge, and the other has a slight negative charge. When water starts going below about 4 degrees Celsius, the molecules start to have a small enough momentum that the charge keeps them further apart from each other than when they were bouncing all over the place at higher temperatures.

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**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\
**Post date:** [September 11, 2001, 11:28pm UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942/3 "2001-09-11T23:28:21Z")

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[http://www.pausd.palo-alto.ca.us/k6science/water/w\_q\_a/expand.html](http://www.pausd.palo-alto.ca.us/k6science/water/w_q_a/expand.html)

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**Author:** ![\_Tim](https://avatars.discourse-cdn.com/v4/letter/_/e47c2d/32.png) [@\_Tim](https://boards.straightdope.com/u/_Tim)\
**Post date:** [September 12, 2001, 12:25am UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942/4 "2001-09-12T00:25:29Z")

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You might want to check out [this thread.](http://boards.straightdope.com/sdmb/showthread.php?threadid=39895)

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**Author:** ![Mac](https://avatars.discourse-cdn.com/v4/letter/m/cc9497/32.png) [@Mac](https://boards.straightdope.com/u/Mac)\
**Post date:** [September 12, 2001, 2:16am UTC](https://boards.straightdope.com/t/why-does-ice-expand/80942/5 "2001-09-12T02:16:11Z")

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Thanks those links were especially usefull.