# Why is water basically incompressible? Are there squishy liquids? **URL:** \ **Category:** Factual Questions\ **Created:** [February 13, 2013, 10:43pm UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227 "2013-02-13T22:43:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [February 13, 2013, 10:43pm UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/1 "2013-02-13T22:43:10Z")
See subjects. Is it a matter of all liquids? ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [February 13, 2013, 11:01pm UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/2 "2013-02-13T23:01:35Z")
Considering that all elements can be compressed to a liquid and then to a solid the incompressability is not a function of the liquid state. Liquid CO2 can be compressed into dry ice, for example. Water acts weird because it’s molecules are electrically polar; that is they have a positive end and a negative end (where the 2 hydrogen atoms are). That’s also why water expands when it freezes. Each positive end has to line up with a negative end in a certain way. Water is pretty fascinating stuff, when you compare it to other substances. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [February 13, 2013, 11:35pm UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/3 "2013-02-13T23:35:20Z")
Most liquids have very small compressibility since there’s not much space between the molecules to move closer. But they are compressible otherwise longitudinal sound waves wound not move through them. Compressibilty is basically an increase in density with pressure. Here’s a table of compressibility of normal liquids - [http://www.engineering.uiowa.edu/~cfd/pdfs/tables/1-42B.pdf](http://www.engineering.uiowa.edu/~cfd/pdfs/tables/1-42B.pdf). You can see which liquids are more compressible and which are less. Cryogenic liquids on the other hand have a density that is not much different from the gas and have greater compressibility. Liquid hydrogen will be the closest match in your search for “squishy liquid”. ---
**Author:** ![Hermitian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hermitian/32/470_2.png) [@Hermitian](https://boards.straightdope.com/u/Hermitian)\ **Post date:** [February 14, 2013, 12:50am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/4 "2013-02-14T00:50:49Z")
They are compressible, but they are routinely considered incompressible for many applications. It’s like calculating the momentum of cars traveling 60-80 mph. Any terms added to the calculation due to relativity are too small to have any major effect on the answer. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [February 14, 2013, 12:59am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/5 "2013-02-14T00:59:00Z")
> [@am77494](#): > > But they are compressible otherwise longitudinal sound waves wound not move through them. Do longitudinal sound waves not also transit solids? ---
**Author:** ![Manlob](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@Manlob](https://boards.straightdope.com/u/Manlob)\ **Post date:** [February 14, 2013, 1:21am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/6 "2013-02-14T01:21:23Z")
Liquids and solids are harder to compress than a gas because the molecules are essentially touching each other in liquids and solids. There is not much special about the compressibility of water, and it is easier to compress than many common materials. For analysis of liquid flow, the liquid is often assumed to be incompressible because the tiny amount of shear force it takes to make the liquid flow is almost nothing compared to what it takes to compress to a comparable strain. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 14, 2013, 1:29am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/7 "2013-02-14T01:29:02Z")
To the second question, “are there squishy liquids”, the answer is by definition “no”: A liquid is an incompressible fluid. There are, however, fluids which are neither liquids nor gases, and which would probably fit reasonably well with your mental image of “squishy liquid”. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [February 14, 2013, 1:37am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/8 "2013-02-14T01:37:42Z")
I guess if you want to test squishy liquids, start with some Jell-O? ---
**Author:** ![Manlob](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@Manlob](https://boards.straightdope.com/u/Manlob)\ **Post date:** [February 14, 2013, 1:48am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/9 "2013-02-14T01:48:13Z")
I don’t think Jell-O would be easy to compress. One of the most incompressible real substance is rubber, even compared to metals like titanium and steel, rubber is harder to compress, but it has a Jell-O-like lack of shear stiffness. To make a liquid more compressible, fill it with bubbles. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [February 14, 2013, 2:09am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/10 "2013-02-14T02:09:20Z")
> [@For You](#): > > Do longitudinal sound waves not also transit solids? yes they do - the longitudinal waves in solids are faster than the transverse waves. The point I was trying to make is that a medium needs to be compressible for compression (longitudinal) waves to propogate ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [February 14, 2013, 2:14am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/11 "2013-02-14T02:14:41Z")
> [@Chronos](#): > > To the second question, “are there squishy liquids”, the answer is by definition “no”: A liquid is an incompressible fluid. Well, yes and no. Liquids are often treated as incompressible fluids, and this approximation is close enough for the vast majority for most engineering and general science problems, but all liquids (and indeed, all substances short of degenerate matter) have some degree of compressibility within all states of matter. Some liquids will undergo may undergo partial thermodynamic state changes due to dynamic environments (e.g. vaporization due to cavitation) which has to be considered, and of course can expand and contract with thermal changes that may be the result of mechanical compression, although the volume change is very small. Solids are generally assumed to be one particular density, but can be permanently compressed to higher density. (I have held an inert steel “pit” that had been compressed by explosives to approximately three times the normal density of steel.) Stranger ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [February 14, 2013, 2:21am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/12 "2013-02-14T02:21:02Z")
sorry ---
**Author:** ![Manduck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manduck/32/256_2.png) [@Manduck](https://boards.straightdope.com/u/Manduck)\ **Post date:** [February 14, 2013, 2:32am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/13 "2013-02-14T02:32:03Z")
> [@Manlob](#): > > To make a liquid more compressible, fill it with bubbles. But then you’re not compressing the liquid, you’re compressing the bubbles. ---
**Author:** ![doubleminus](https://avatars.discourse-cdn.com/v4/letter/d/5daacb/32.png) [@doubleminus](https://boards.straightdope.com/u/doubleminus)\ **Post date:** [February 14, 2013, 2:33am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/14 "2013-02-14T02:33:37Z")
Did that steel pit regain its original volume afterwards? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 14, 2013, 4:21am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/15 "2013-02-14T04:21:06Z")
> [@For You](#): > > Do longitudinal sound waves not also transit solids? Yes, because solids are compressible. Slightly. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [February 14, 2013, 4:33am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/16 "2013-02-14T04:33:01Z")
> [@Manlob](#): > > One of the most incompressible real substance is rubber… 😕 As opposed to a virtual substance, or an imaginary one? ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [February 14, 2013, 4:43am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/17 "2013-02-14T04:43:25Z")
> [@Stranger\_On\_A\_Train](#): > > Some liquids will undergo may undergo partial thermodynamic state changes due to dynamic environments (e.g. vaporization due to cavitation) I guess I always thought of cavitation as being primarily due to the dissolved gasses being beaten out of the water (thinking of propellers), but I could see that the back edge of a propeller might reduce the pressure in the water below its vapor pressure. I would assume that most of the water would recondense pretty quickly but some might bubble out? > [@](#): > > … and of course can expand and contract with thermal changes … Like alcohol or mercury in a thermometer. ---
**Author:** ![drewtwo99](https://avatars.discourse-cdn.com/v4/letter/d/d07c76/32.png) [@drewtwo99](https://boards.straightdope.com/u/drewtwo99)\ **Post date:** [February 14, 2013, 5:01am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/18 "2013-02-14T05:01:54Z")
Throw some water or other liquid into a black hole or neutron star and then tell me how incompressible it is! The correct answer as given above is that the compressibility of most liquids is negligible and insignificant in nearly all applications. ---
**Author:** ![j\_sum1](https://avatars.discourse-cdn.com/v4/letter/j/8baadc/32.png) [@j\_sum1](https://boards.straightdope.com/u/j_sum1)\ **Post date:** [February 14, 2013, 5:16am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/19 "2013-02-14T05:16:43Z")
I once worked in a place that did waterjet cutting. The water velocity at the nozzle was more than twice the speed of sound and the operating pressure to achieve that was 50000psi. The water compressed by around 12% in the process. All substances can be compressed. However, for most contexts the compression of liquids can be considered to be negligible. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [February 14, 2013, 5:53am UTC](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227/20 "2013-02-14T05:53:09Z")
Since liquids compress so little, I wonder: does it take more energy to compress a gas than a liquid to the same pressure? Does that mean compressed gas tanks are more dangerous? [Next page](https://boards.straightdope.com/t/why-is-water-basically-incompressible-are-there-squishy-liquids/650227.md?page=2)