If Gas is the only state of matter where you can change the density with pressure, how can you pressurise liquids like water?

Question

I know that solids and liquids can’t change density without changing their molecular structure, so how do things like oil pressure and water pressure exist?

In: Physics

Answer 1

Solids and liquids do compress, but by much, *much* less than gasses do. For gasses, volume is inversely proportional to pressure: multiply pressure by X, divide volume by X.

For water, on the other hand, you need *lots* more pressure to get a significant volume change. It takes about 3,000 psi (~200 atmospheres!) to compress water by even 1%. So for most practical engineering purposes, you can take liquids to be incompressible and not be very wrong. Some solids are even harder to compress: steel, for example, takes ~230,000 psi to compress by 1%.