why liquids are considered “incompressible,” while gasses and solids can be compressed?
In: Physics
Liquids are compressible, although eventually with enough pressure they will just turn into a solid. Very rarely do you do something with a liquid where it’s compressibility is relevant to the calculation.
With something made from solid materials, it’s compressibility (and tensile properties) governs how it bends and squashes in each axis and its important to the structures stiffness. Its easy to put huge forces through small amounts of material, so how it compresses and stretches is very relevant. With liquids, the compressibility only matters when you directly compress them and not many things need to run at particularly high pressures.
Air pressure at sea level is about 1 bar.
At the bottom of the mariana trench the water pressure is about 1000 bar, water is about 5% denser.
Typical hydraulics on diggers run run at about 300-400 bar, compression of the oil is only a couple of percent.
In high pressure fuel systems on diesel engines which run about 2000-2400 bar, how much the fuel compresses is pretty important. This is by far the highest pressure everyday application I can think of.
Water jet cutters run at over 6000 bar. Water has a decent volume change at this point.
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