Eli5 : if pressure is due to the size of the column of fluid above, why is it not lighter inside ?

Question

I know that if you are inside of a hermetic room, the pressure is the same. But I can’t understand *why*. For example, if you enclose water from the bottom of the ocean in a box, shouldn’t it be suddenly at the same pressure than outside, due to the fact there is not the weight of the water column above ?

Thanks!

In: 2

Answer 1

If you enclose the water at the bottom of the ocean, then you have enclosed water that is already pressurized, so it stays pressurized. If you brought it to the surface, it would still be pressurized, the container would try to expand outwards. I suppose at theoretically perfect liquid with no dissolved gasses might not still be pressurized, because it wouldn’t compress under load.