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/sci/ - Science & Math

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5134055 No.5134055 [Reply] [Original]

hello /sci/
im working on a physics lab and i have a massive brain fart.

i need to graph ln(p) vs. ln(v). which goes on the x-axis and which on the y-axis.

i think its the ln(p) on the y-axis no?

>> No.5134060

bump

>> No.5134070

bump, please please

>> No.5134085

Were you physically changing the volume or were you changing the pressure?

>> No.5134099

>>5134055
It really is a matter of choice, if there's a definite answer we can't tell you what it is because that's up to the grader. In general though, the thing that either you're manually varying or that changes constantly (evenly) over time is the x axis, the "independent variable"

>> No.5134104
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5134104

Yes, ln(p) would be the y-axis. And don't worry, I'm a chemical engineer and still have to look this up sometimes lol

>> No.5134105

>>5134085
>>5134099
its an adiabatic lab, we changed the volume rapidly which led to a change in P and T as well as V.

the graph it to solve for the Cp/Cv ratio (gamma) and i need to graph it correctly in order to get a correct value for gamma

>> No.5134107

>>5134104
ok thank you, yes i always forget this

>> No.5134111

also while im here, for the ideal gas law, P is in pascals and V is in m^3 right? thats how i did it and i think its correct units.

>> No.5134121

My way to read this is:
- People used to tell you "graph f(x)",
- They basically meant "graph f(x) vs x",
- Thus "graph ln(p) vs ln(v)" means ln(p) is what used to be the y-axis f(x), and ln(v) is what used to be x.

However honestly the only difference between the graphs of ln(p) vs ln(v) and ln(v) vs ln(p) is a symmetry over the first diagonal, so you can read one just as easily as you can read the other. As a grad student, I remember that different authors graphed things using the reversed axes. It was confusing at first (you were used to seeing some "shapes" and suddenly they didn't mean the same thing), but as long as you label your axes and know what you're doing, you're fine.

>> No.5134122

>>5134105

If you're varying volume, then volume goes on the x axis.

>> No.5134188

Personally, I would graph it however the hell I wanted to and justify it by clearly demonstrating that you understand what is being graphed.