I understand that pressure is F/A. But whenever they ask me to find the pressure of a book acting on the table, since the object in question is actually the table so is the force the reaction force on the table by the book and not actually weight since weight is an internal force? Again, with the hydraulic system information in my textbook a small force acting on a small piston gives rise to a large force in the large piston as the pressure is the same. But I'm quite confused as they say that a forfeit is exerted on the piston. I thought that the object that we have to take into perspective is the liquid? Also since my force is acting the piston that force's area has to be the same as the piston's or else the pressure won't be the same since P=F/A. I'm not very sure about this since all they say is the force on the piston so I don't quite understand it in detail. Lastly, pressure in a liquid acts at all directions. What does this mean? Does it mean that when I use P=hpg to get the pressure in the liquid (taking that there is no atmospheric pressure above) that pressure acts at all directions? But won't that mean that the force is infinite since the pressure acts at all direction so P=F/A is infinite as at one point upwards pressure is same as downwards. Thanks guys for the help! Hope to hear (or read) from you guys soon!