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

Simple answer: you use a pump. You can’t really *compress* a liquid, but you can push it. In most cases you need *flow* more than anything else, and the pressure created is the reaction force from the fluid being pushed by the blades of the impeller.

But, let’s say you have a weird case where you need a liquid at a high pressure (this does happen, sometimes you want to get water really hot without actually boiling it). What you do in that case is leave some space at the top of the tank, and have a compressor squeezing a gas into that space. Whatever pressure the gas is at will be the same in the liquid.