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

I’m sure I don’t understand your question.

Water pressure is only acting on the outside of the container and not on the air inside of it. That’s how people can take submarines down to deep places like the Challenger Deep or the wreck of the Titanic, despite there being enough pressure down there to basically crush them like an empty pop can.