Pressure in fluids.... I have been looking at derivation of the equation Pressure in fluids= height of fluid column*density*gravitational field strength, from the intitial starting point of P = F/A and taking F to be weight of column. But I have since read that the pressure is not in fact due to the weight of the fluid but due to collisions between its molecules and some object, and that in fact the pressure acts from all directions, not just down. So if this is the case, then why does the equation I have previously mentioned hold, even for an upward or sideways pressure? Thanks in advance.