/sci/ - Science & Math » Thread #11092877

113KiB, 960x720, slide_6.jpg

View Same Google iqdb SauceNAO

Anonymous Sat 26 Oct 14:00:36 2019 No.11092877 View Reply Original Report

Quoted By: >>11092917 >>11092927 >>11093552 >>11093564 >>11096476 >>11097909

PV=nRT
If i pish a piston down , does T increase or decrease ?
The pressure is increasing but the volume is decreasing.
Also why does an expanding gas loose heat , according to the equation an increase in volume should increase temperature.

Fuck chemistry

Anonymous

View Same Google iqdb SauceNAO rvkf32FkSuO9QfJ7sEst_Carnot-cycl (...).png, 12KiB, 599x421

Anonymous Sat 26 Oct 2019 14:19:40 No.11092917 Report

Quoted By: >>11092925 >>11092960

>>11092877
>does T increase or decrease ?
Assuming no heat transfer with the surrounding, T will increase.
>why does an expanding gas loose heat
If you plot the process on a PV diagram you will see that constant temperature (heat transfer occurs) expansion/compression makes a path that is the shape of a hyperbola. Adiabatic processes, in which there is no heat transfer, are steeper than constant temperature hyperbolas. So when you compress adiabatically, you "climb" to an higher isotherm. Pic rel. This is not a formal explanation but can help you understand what's happening.
>increase in volume is increase in T
Only if all other variables are constant. How often do you expand a gas and its pressure is constant? Pretty much never. This only happens when you add heat while the gas expands. Usually gasses do work when the expand, so the opposite occur.

>fuck chemistry
Agreed but thermo is based. Just keep practicing anon :3

Anonymous

Anonymous Sat 26 Oct 2019 14:24:10 No.11092925 Report

Quoted By:

>>11092917
>Agreed but thermo is based.

stat thermo fucked me harder than any other physics/math course but it gave me immense respect for the theory.

Anonymous

Anonymous Sat 26 Oct 2019 14:24:36 No.11092927 Report

Quoted By: >>11092942 >>11092960

>>11092877
You're missing the other equation dU = dQ - dW, change in internal energy of the system is equal to heat added to the system minus work done by the system. So it depends, really. If you treat the piston as insulated so that dQ = 0 then the temperature also goes up because dW is negative resulting in a positive dU. But you can also imagine a piston that is fully thermally conductive so T and hence U is constant, meaning dQ = dW, so heat is constantly flowing out of the system at the same rate that work is done on it.
tldnr: it depends on "how" you compress it.

Anonymous

Anonymous Sat 26 Oct 2019 14:28:13 No.11092942 Report

Quoted By: >>11092949 >>11094214

>>11092927
>dQ
>d
REEEEEEE

Anonymous

Anonymous Sat 26 Oct 2019 14:29:57 No.11092949 Report

Quoted By: >>11092956

>>11092942

>mathfag btfo

Anonymous

Anonymous Sat 26 Oct 2019 14:31:21 No.11092956 Report

Quoted By: >>11093558

>>11092949
Im an engie. I just like the way the deltas look, makes it look more sophisticated than it is

Anonymous

Anonymous Sat 26 Oct 2019 14:32:19 No.11092960 Report

Quoted By: >>11092980 >>11093033

>>11092917
>>11092927
Cool guys but explain this shit in high school terms plz

Anonymous

View Same Google iqdb SauceNAO 1571002251247.png, 60KiB, 322x330

Anonymous Sat 26 Oct 2019 14:39:32 No.11092980 Report

Quoted By: >>11092998

>>11092960
Change in internal engery = heat added - work done by fluid
(This is literally just the conservation of energy)

In your scenario, you are compressing the gas. Work done by fluid = boundary work = (pressure)(change in volume). The change in volume is negative and so boundary work overall is negative. No heat is added. Thus we have it that the change in internal enerfy is dU= -(boundary work) which is a positive quantity.
Internal energy U is a function of temperature, and so a positive change in U means U increases means T has increased.

Anonymous

Anonymous Sat 26 Oct 2019 14:44:03 No.11092998 Report

Quoted By: >>11093003 >>11093012

>>11092980
No temeperature is added yet temperature increased ?
What's the equation describing U as a function of temperature . Sorry if i sound like a retard just bear with me

Anonymous

Anonymous Sat 26 Oct 2019 14:46:05 No.11093003 Report

Quoted By:

>>11092998
Temperature=/=heat
Not even close. No heat is added. The temperature still increases. If you don't believe me, go get a bike pump and compress it very quickly. It will get warm.

Anonymous

Anonymous Sat 26 Oct 2019 14:49:39 No.11093012 Report

Quoted By:

>>11092998
>What's the equation describing U as a function of temperature
U=CvNT where Cv is heat capacity at constant volume. N is moles. T is temperature. But this is only for an ideal gas.
In real life, engineers use tables that are compiled from thousands of experiments to figure out what U would be.

Anonymous

Anonymous Sat 26 Oct 2019 14:58:14 No.11093033 Report

Quoted By:

>>11092960
fundamentally, heat is molecules bouncing off each other
if you compress them, they get less elbow room start hitting each other more
if you suddenly give them more space, they stop hitting each other as the probability of collision decreases

Anonymous

View Same Google iqdb SauceNAO dumb.png, 89KiB, 1551x636

Anonymous Sat 26 Oct 2019 17:55:41 No.11093409 Report

Quoted By: >>11093496 >>11093524

Retard here. Why the fuck is the 50cm being multiplied by 10^-4 when dividing the 100N instead of being converted to meters?

Anonymous

Anonymous Sat 26 Oct 2019 18:25:16 No.11093496 Report

Quoted By: >>11093560

>>11093409
Someone help this dude

Anonymous

Anonymous Sat 26 Oct 2019 18:36:42 No.11093524 Report

Quoted By: >>11093560

>>11093409
It’s area so the 10^-2 conversion factor becomes 10^-4

Anonymous

Anonymous Sat 26 Oct 2019 18:49:06 No.11093552 Report

Quoted By:

>>11092877
Oh wow how are your entry level high school classes doing?

Just kidding, fuck off. /sci/ isn't for homework requests

Anonymous

Anonymous Sat 26 Oct 2019 18:50:32 No.11093558 Report

Quoted By:

>>11092956
Unironicaly true

Anonymous

Anonymous Sat 26 Oct 2019 18:51:04 No.11093560 Report

Quoted By:

>>11093496
>>11093524
Yeah I realised that I had to convert to ^2 units

Anonymous

View Same Google iqdb SauceNAO 4F7D320F-F8F4-44F4-B9FA-E5618EF0 (...).jpg, 28KiB, 301x475

Anonymous Sat 26 Oct 2019 18:53:28 No.11093564 Report

Quoted By:

>>11092877
Read Callen.

Anonymous

Anonymous Sat 26 Oct 2019 22:42:59 No.11094214 Report

Quoted By:

>>11092942
eh I would have put the slash thru it but too hard to type. Yeah its path-dependent

Anonymous

Anonymous Sun 27 Oct 2019 18:17:28 No.11096476 Report

Quoted By:

>>11092877
Why is the control knob buried inside the thermal reservoir?

Anonymous

Anonymous Mon 28 Oct 2019 02:29:51 No.11097909 Report

Quoted By:

>>11092877
Yes, and it also works other way around. This is why the spray can gets cold and why you should keep distance when spraying something on yourself to avoid frostbite

Capcode	All Only User Posts Only Moderator Posts Only Admin Posts Only Developer Posts
Show Posts	All Only With Images Only Without Images
Deleted Posts	All Only Deleted Posts Only Non-Deleted Posts
Ghost Posts	All Only Ghost Posts Only Non-Ghost Posts
Post Type	All Only Sticky Threads Only Opening Posts Only Reply Posts
Results	All Grouped By Threads
Order	Latest Posts First Oldest Posts First

Your latest searches