# Yet another stupid physics question **URL:** \ **Category:** Factual Questions\ **Created:** [June 25, 2010, 3:32pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492 "2010-06-25T15:32:43Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Vorpal\_Blade](https://avatars.discourse-cdn.com/v4/letter/v/9de0a6/32.png) [@Vorpal\_Blade](https://boards.straightdope.com/u/Vorpal_Blade)\ **Post date:** [June 25, 2010, 3:32pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/1 "2010-06-25T15:32:43Z")
Why do (putatively neutral) molecules attract each other? As a gas cools, it condenses into a liquid, still cooler it becomes a solid. I assume this is because the molecules (or atoms) are mutually attractive. How come that is? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [June 25, 2010, 3:37pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/2 "2010-06-25T15:37:06Z")
Why would you assume that it has to do with attraction? Do you mean magnetic attraction? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 25, 2010, 4:02pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/3 "2010-06-25T16:02:35Z")
[London Dispersion Forces](http://www.chem.purdue.edu/gchelp/liquids/disperse.html), also [Van der Waals forces](http://en.wikipedia.org/wiki/Van_der_Waals_force). ---
**Author:** ![Vorpal\_Blade](https://avatars.discourse-cdn.com/v4/letter/v/9de0a6/32.png) [@Vorpal\_Blade](https://boards.straightdope.com/u/Vorpal_Blade)\ **Post date:** [June 26, 2010, 9:21am UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/4 "2010-06-26T09:21:42Z")
> [@KneadToKnow](#): > > Why would you assume that it has to do with attraction? …snip…? Because if the molecules weren’t attracted to each other they’d all wander off. A gas, as it cooled wouldn’t form a liquid, just a cooler gas. My question can be rephrased, “Why form a liquid, why not just form a cooler gas?” ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [June 26, 2010, 8:08pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/5 "2010-06-26T20:08:03Z")
> [@Vorpal\_Blade](#): > > Why do (putatively neutral) molecules attract each other? As a gas cools, it condenses into a liquid, still cooler it becomes a solid. I assume this is because the molecules (or atoms) are mutually attractive. How come that is? I don’t think that’s a stupid question. I studied physics and thermodynamics for years and I didn’t know the answer. Not only that, but until I read your question and thought about it, I didn’t even know I didn’t know. So I think it’s an excellent question! Thanks Squink, I had never heard of London dispersion forces before, and it’s clear from that link that they are very important in explaining everyday phenomena. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [June 26, 2010, 8:18pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/6 "2010-06-26T20:18:06Z")
Quick’n’dirty: A molecule can be neutral overall, but have its charge asymmetrically distributed, so bits of it are more positive or more negative. That gives you a basis for molecules to attract each other, although the forces aren’t as strong as those that hold the molecules themselves together. Forces like this account for the way that proteins interact - different parts of a protein are attracted to corresponding parts of another, without which DNA wouldn’t work. So this simple-seeming question actually relates to the workings of the building blocks of life itself! ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 26, 2010, 8:28pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/7 "2010-06-26T20:28:32Z")
> [@Malacandra](#): > > Forces like this account for the way that proteins interact Well, that and the [Casimir effect](http://en.wikipedia.org/wiki/Casimir_effect). ---
**Author:** ![The\_Urban\_Spaceman](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@The\_Urban\_Spaceman](https://boards.straightdope.com/u/The_Urban_Spaceman)\ **Post date:** [June 26, 2010, 8:28pm UTC](https://boards.straightdope.com/t/yet-another-stupid-physics-question/544492/8 "2010-06-26T20:28:44Z")
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