Answer:
The reason we can't feel it is that the air within our bodies (in our lungs and stomachs, for example) is exerting the same pressure outwards, so there's no pressure difference and no need for us to exert any effort.
funny, actually, i'm a hydraulic, and pneumatic cylinder, pump, and line system mechanic, and the answer is pressure.... pressure builds up from the hydraulic pump, and then transfers through hoses to extend, and contract the cylinders by filling them with hydraulic fluid, and vice versa for contracting them.
hope this helps!
I think i used calulater and it gives me 47.5