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### Pressure of gasses

Posted: Fri Jan 11, 2019 10:56 am
On page 151 of the 6th edition of our textbook there is an equation: P=dhg which solves for the pressure of a gas based on the height of a column of liquid and its density and gravity. I was wondering if we would need to know this calculation, if so can someone please explain it in depth because the explanation in the textbook slightly confuses me.

### Re: Pressure of gasses

Posted: Fri Jan 11, 2019 11:14 am
I dont think we will be using this equation since he hasnt mentioned it in lecture and all HW problems are solvable without the equation.

### Re: Pressure of gasses

Posted: Fri Jan 11, 2019 3:24 pm
I think stick to the formulas he has given us in lecture so far, bc this one hasn't been mentioned yet.

### Re: Pressure of gasses

Posted: Fri Jan 11, 2019 5:28 pm
Yeah just to confirm the above responses, Dr. Lavelle hasn't gone over that equation so I don't think we have to know that one. For now at least.

### Re: Pressure of gasses

Posted: Fri Jan 11, 2019 7:42 pm
I don't think we will be using it. He hasn't mentioned it in lecture yet.

### Re: Pressure of gasses

Posted: Sat Jan 12, 2019 12:03 am
This is more of a physics topic but if your interested this is the general idea:
To calculate the weight of the liquid we use the equation: weight (force)=mg (mass x gravity constant). The mass of the liquid can be determined using both the volume of the liquid and its density (m=Vd : where V=volume and d=density). Combining these equations we now get F=Vdg.The volume of a cylinder of liquid can be determined using the geometric formula V=A (of the circle) x h (height of the liquid). Using this equation we now get: F=Ahdg
Now, the definition of pressure is Force/Area, so combining the equations above we get P=(Ahdg)/A which when simplified yield P=hdg Tadaaaaa.