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# Need help on a thermodynamics graph please

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posted on Oct, 2 2012 @ 08:59 PM
I am helping a friend study for a test, but dont understand the graph, it doesnt seem to make any sense to me, someone please help!!!

www.4tests.com...

I didnt know how to embed the image, sorry.

If anyone could please educate us on the way to read this particular graph I would be very greatful!

ETA- it asked if the pressure is 8 what is the volume? But to me it looks like the volume matches the pressure across the board so the volume would be an 8 as well, however this is the wrong answer. So we have no idea what the right answer would be or more important, how to interpret the graph to find the data in the first place.
edit on 2-10-2012 by inverslyproportional because: (no reason given)

posted on Oct, 2 2012 @ 09:03 PM

It shows the inverse relationship between pressure and volume. As the pressure increases, the volume decreases.

ETA: Boyle's Law

You look on the graph where the pressure (bottom axis) is 8, go to where the curve is, look to the left and it appears the volume is 2 (half of 4).

edit on 2-10-2012 by PurpleChiten because: (no reason given)

posted on Oct, 2 2012 @ 09:07 PM

Assuming constant temperature within the system.

posted on Oct, 2 2012 @ 09:08 PM

Originally posted by TomServo

Assuming constant temperature within the system.

Yup

posted on Oct, 2 2012 @ 09:11 PM
If you use the formula: pV=k , you see that when the pressure is 4, the volume is 4 so (4)(4)=16. To find either of the other values given one of the values, you substitute in.
When the pressure is 8; 8V=16, solve for V and you see that V=2

posted on Oct, 2 2012 @ 09:14 PM

Yes, but I still do not understand the way to read it, we need an explanatin as to what we are reading wrong here.

As it reads to me, it appears that the answer would be 2 but that is not correct, I don't really want the answer so much as the means to arrive at it. I don't seem to be able to see what my mistake is.

I swear it looks to me like, if the pressure is 8 then the volume would be a 2, but am not sure myself, as 8 am unfamiliar with this kind of graph.

posted on Oct, 2 2012 @ 09:15 PM

Originally posted by inverslyproportional
ETA- it asked if the pressure is 8 what is the volume? But to me it looks like the volume matches the pressure across the board so the volume would be an 8 as well,
FYI if the pressure matched the volume across the board, the shape of the curve would be a straight line from the origin (lower left) at a 45 degree angle to the upper right. So of course that's not what it shows, but I thought I'd mention that so you know what to look for if that ever happens on a graph, which sometimes it might, though it wouldn't happen with pressure and volume.

posted on Oct, 2 2012 @ 09:21 PM

Thank you sir! Duh!!! Lol I feel so dumb now, I should have seen that for what it is, I don't know what I was thinking. Stars for you guyhs thanks!

posted on Oct, 2 2012 @ 09:21 PM

Originally posted by inverslyproportional

Yes, but I still do not understand the way to read it, we need an explanatin as to what we are reading wrong here.

As it reads to me, it appears that the answer would be 2 but that is not correct, I don't really want the answer so much as the means to arrive at it. I don't seem to be able to see what my mistake is.

I swear it looks to me like, if the pressure is 8 then the volume would be a 2, but am not sure myself, as 8 am unfamiliar with this kind of graph.

The answer is, indeed, 2. You read the graph by looking at the curve that is formed, then looking at the x and y coordinates that coorelate to that point on the graph. When the pressure is at 8, the volume is at two. (also when the volume is at 8, the pressure is at 2).
Perhaps you need to include units in your answer in order for it to accept it.

posted on Oct, 2 2012 @ 09:23 PM

Originally posted by inverslyproportional

Thank you sir! Duh!!! Lol I feel so dumb now, I should have seen that for what it is, I don't know what I was thinking. Stars for you guyhs thanks!

Welcome

Noticed your screen name is "inverslyproportional", which is exactly what the graph shows, inverse proportionality

posted on Oct, 2 2012 @ 10:22 PM

Originally posted by PurpleChiten
Noticed your screen name is "inverslyproportional", which is exactly what the graph shows, inverse proportionality
Not exactly. Inverse proportionality is linear as the first graph in this link shows for the equation y=-2x+3:

mathonweb.com...

The form of inverse proportionality is a straight line sloping down and to the right.

The curve in the OP is not inversely proportional (because for one thing, it's not a straight line), it's called a power function. See the 4th graph down at that same link for some examples and comments about the math of a power function.

posted on Oct, 3 2012 @ 05:15 AM

Originally posted by Arbitrageur

Originally posted by PurpleChiten
Noticed your screen name is "inverslyproportional", which is exactly what the graph shows, inverse proportionality
Not exactly. Inverse proportionality is linear as the first graph in this link shows for the equation y=-2x+3:

mathonweb.com...

The form of inverse proportionality is a straight line sloping down and to the right.

The curve in the OP is not inversely proportional (because for one thing, it's not a straight line), it's called a power function. See the 4th graph down at that same link for some examples and comments about the math of a power function.

You are extremely incorrect. You are thinking of a negative slope. The graph he linked to is EXACTLY inversely proportional.

posted on Oct, 3 2012 @ 05:18 AM

zonalandeducation.com...

posted on Oct, 3 2012 @ 10:19 AM

Thanks, I stand corrected, I guess I needed a stronger cup of coffee, because I knew that, sorry.

posted on Oct, 3 2012 @ 03:36 PM

Originally posted by Arbitrageur

Thanks, I stand corrected, I guess I needed a stronger cup of coffee, because I knew that, sorry.

It's all good

A mistake isn't bad unless you fail to correct it. Early mornings and math doesn't always mix!

posted on Mar, 27 2015 @ 07:43 AM
Early mornings and anything don't really mix but there's and excellent KPI dashboard at Datapine that takes out some of the manual calculation when you're dealing with lots of data. They provide excellent visualisations that give you a much better feel for the numbers. Its really easy to use too. Take a look.
edit on 27-3-2015 by secretcarver because: s

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