# Are liquids compressible?

If we take a cyclindrical container, fill any liquid upto certain level and then put a piston such that it touches the surface of water. If we start compressing the liquid, will the liquid compress? Assuming the walls to be perfectly rigid...this questoin arised from the topic ,"are liquids compressible"?

## Popular Answers

Iris Andrea Pantle· Falquez, Pantle und Pritz GbRa) Ma < 0.2 can be approximated as incompressible (means: it is rather unlikely - though not impossible - that compressibility effects appear and are strong),

b) Ma > 0.7 should/must be considered compressible (also liquids!!!),

c) in between it depends on the type of flow and the attached geometry whether compressibility effects are too strong to be neglected.

Egon Hassel· University of Rostock## All Answers (41)

Jim PohlManuel Garcia· University of ZaragozaThey are compressible but just a little bit. For example, liquid water changes its density (at ambient temperature) 0,024% with a change of 500 kPa in pressure.

Regards, Manuel

Archak Goel· University of CincinnatiNesma Abo Shanb· Alexandria Universityand from which the idea of the hydraulic press is made..

but it's classical physics cuz i didn't study modern yet ..

Subhash Guruji· CENTURY COOLINGArchak Goel· University of Cincinnati2) it is always [ossible to lessen the inter molecular spaces in matter, its just amount of force that matters.

3) had liquid not beeen compressible, then how could the sound wave travel in it??? as the wave propagates by compressing and letting the medium to expand..

Hence i suppose it is compressible theoritically.

Dimitar Efendulov· Independent ResearcherThe brake fluid doesn't work like that... You compress a bit on a big piston, then the fluid compresses a lot a small piston ;)

In my opinion liquids are compressible, but it is so negligible that we say they are incompressible...

Nesma Abo Shanb· Alexandria Universityso i may say that liquid is a bit compressible ..

Ty guys for widen my knowledge :)

Egon Hassel· University of RostockDenis A. Walsh· Excel SystemsAgnimitra Sunkara· National Aerospace LaboratoriesYuri Shakhov· KhAI - Aerospace universityArchak Goel· University of CincinnatiByron Wooldridge· AES Deepwater, Inc.Vigneswaran Rajendiran· s.b.c engg college,arni, TNVigneswaran Rajendiran· s.b.c engg college,arni, TNAli Volkan Akkaya· Yildiz Technical UniversityShripad Arun Upalkar· College of Engineering, PuneDenis A. Walsh· Excel SystemsPressure/Temperature ratio relative to mass.

Ram M S· SASTRA UniversityGenerally all fluids are compressible and in case of liquids, the compress ability is less and hence for solving purposes they are considered to be zero. Technically compression is nothing but change of density. The change of density of liquid is negligible and hence it is considered zero. The question is same like "whether the world is rotating?" It is but is relatively considered as zero.

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Ram M S· SASTRA UniversityGenerally all fluids are compressible and in case of liquids, the compress ability is less and hence for solving purposes they are considered to be zero. Technically compression is nothing but change of density. The change of density of liquid is negligible and hence it is considered zero. The question is same like "whether the world is rotating?" It is but is relatively considered as zero.

Got It?

Ram M S· SASTRA UniversityDeletedMurugan Natarajan· Vel Tech Rangarajan Dr Sagunthala R&D Institute of Science and Technologyit is nothing but the fractional change in volume of the fluid element as a result of pressure applied on the fluid element .

For the case of liquids the compressibility is less ( change in volume of fluid element is negligible for the given applied pressure) , then it is assumed to be incompressible fluid .

Edward E. Anderson· Texas Tech UniversityAntonio OfExovaIssam Sinjab· Alumni University of Leicester & University of SussexThe differentiation of a liquid as an incompressible fluid is not strictly correct, experiment have shown that liquids are compressible to a very limited extent.

So, for example, for each atmosphere increase in pressure, the volume of water would decrease 46.4 parts per million. (Data from Sears,Zemansky, Young and Freedman, University Physics, 10th Ed., Section 11-6. )

Maganapal singh Chauhan· Heavy Water Plantgas molecules are far away than liquid,

liquid molecules are also far away than solid.

If we compress liquid at very high pressure, molecular distance can be reduced, so we can say slightly compressible.

Iris Andrea Pantle· Falquez, Pantle und Pritz GbRa) Ma < 0.2 can be approximated as incompressible (means: it is rather unlikely - though not impossible - that compressibility effects appear and are strong),

b) Ma > 0.7 should/must be considered compressible (also liquids!!!),

c) in between it depends on the type of flow and the attached geometry whether compressibility effects are too strong to be neglected.

Maganapal singh Chauhan· Heavy Water PlantBoris Kompare· University of LjubljanaBoris Kompare· University of LjubljanaJerzy Zenon Klimkowski·Archak Goel· University of CincinnatiDeletedJerzy Zenon Klimkowski·Iris Andrea Pantle· Falquez, Pantle und Pritz GbR@Archak: I should add, that I always look from the perspective of moving fluids or movements in fluids. Considering non-moving fluids (i.e. macroscopically non-moving where local movements due to thermal effects or initial shock-type pulses or other forcing mechanisms might appear), one is recommended to dig into the basics of thermodynamics interdependencies between pressure, density, temperature etc. Still then, compressibility of liquids is clearly proved though it might be small. The pure existence of the speed of sound in continua comprising fluids and solids (in addition to and not to be mixed up with the particle velocity, might it be of fluctuating or transporting type) can be considered a proof.

Archak Goel· University of CincinnatiJerzy Zenon Klimkowski·Chuck G. Johnson· Gilson, Inc.All materials in our known universe are compressible regardless of state (solid, liquid gas). Adjectives such as little, small, large, etc are not very helpful because weather or not to consider compressibility depends on the problem at hand. Any time the speed of sound is of interest one must know the compressibility of the material. The effect of of the compressibility of air at flight speeds less than ~.2 Mach on lift and drag are second order effects. The effect is not zero however.

The original question is interesting in a couple of aspects. The question should be posed "if we apply a pressure will the water compress". The pressure is applied via the piston. The answer is an unequivocal yes.

An interesting second question might be "can the compression be measured?". If the cylinder has a cross sectional area of 1 mm^2 and the un-pressurized water column height is 100 mm then the original volume is 100 mm^3. Each newton applied to the piston will generate 1MPa (1,000,000 n/m^2). The compressability of water is ~4.6e-10 (1/Pa). So for each Newton applied to the piston the volume decreases by 1MPa * 4.6E-10*100mm^3 = 0.046 mm^3. Dividing by the cross sectional area of 1mm^2 gives a height change of the piston of 0.046mm. Applying 10 Newtons gets a height change of .46mm. This is a measurable quantity. The trick is building a cylinder/piston and seal system that can withstand the pressure.

Archak Goel· University of CincinnatiHi Chuck!

I had posted this question 3-4 years back while I was in Bachelors program...and yet I agree this is the most simplified and reasonable answer to this post! Thanks for sharing~

Can you help by adding an answer?