Ok first off, I got the answer so this should be simple to answer for someone who understands the theory. Sadly I must admit, the equation I used I have no real information behind it and I simply need to learn how it works and why I need to use it. First I will give you the problem: An air bubble has a volume of 1.70 cm3 when it is released by a submarine 115 m below the surface of a lake. What is the volume of the bubble when it reaches the surface? Assume the temperature and the number of air molecules in the bubble remain constant during its ascent Simply P2=P1+hdg is the equation I started with. P2=(1.013 x 10^5)+115(1025)(9.8)= 12.56 x 10^5. First off what is this equation called, It was given to me out of thin air and I am assuming its a simply equilibrium equation of Pressure? Second the (hdg) H=height D= ??? G= Gravity. Is 1.013 x 10^5 atmoshperic pressure? I thought simply 1 was? Where did D=1025 come from? I am lost here. I finished the problem using V=((P2V2)/P1) and I got the right answer. Now i need to understand where the two variables came from. 1.013 x 10^5= 1atm?????????????? D=1025?????????? Also if you are feeling frisky please identify these equations and give me a brief explanation on why they work please. I am totally lost.