When we suck a straw, we produce a vacuum in our mouths hence the atmospheric pressure on the outside is greater than of the liquid above the straw hence pushing the liquid up. But what if we arrest underwater and we open our mouth, why would water flow into it? Is it because our mouth has a smaller pressure than the surrounding water, so it seeks to reach equilibrium so it flows into it? Also, what allows fluid to flow about at constant and random motions? Is there a pressure explanation for this? When we use thee formula P=hpg at a certain point is that theft pressure exerted on whatever is below it? Eg I have a 10m water tank and if I use hpg at 5m, then is that the pressure exerted on the water molecules below it? Lastly, if I have a box placed into the water, the pressure at the base (parallel to the bottom) is acting upwards right, after calculating the P=hpg at that point. However, if I have a larger surface area box placed instead it will still have the same pressure at that point right? So would the force acting also be larger? As for evaporation, since the water absorbs heat energy from the surrounding our body would be cooler right? But when the enter molecules at the surface of the water body gains enough energy then it would break free its bonds and escape as a gas, so does it mean that the water at the surface is at 100 degrees celcius? So if there is some gas in the air won't it be very hot? Thanks for the help guys!