# What happened to the degree of freedom thread?

1. Sep 20, 2005

### rbj

What happened to the "degree of freedom" thread??

here's the summary of the thread that i got via email:

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degree of freedom
Posted by: kidia
On: 09-18-2005 03:07 PM

Can any body can give me the formula for determine the number of degree of freedom of molecules undergoing translation,rotation and vibration of n number of atom.
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Posted by: rbj
On: 09-18-2005 04:49 PM

it depends on what the molecules are. monatomic? (it's 3n.) diatomic? (it's 5n). more than that, i dunno.
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Posted by: kidia
On: 09-18-2005 09:29 PM

rbj can u clariyfy more if that 3n for monotomic and 5n for diatomic is for translation,rotation or vibration

2. Sep 20, 2005

### ZapperZ

Staff Emeritus
Have you tried looking in the HOMEWORK section?

Zz.

3. Sep 20, 2005

### Staff: Mentor

It was moved to the College Help section. (Just click the links in your post.)

4. Sep 20, 2005

### rbj

why isn't there a little "moved" arrow showing this? like there is for other moved posts?

5. Sep 20, 2005

### Staff: Mentor

To reduce screen clutter. See the sticky at the top of this forum.

6. Sep 20, 2005

### rbj

well, i didn't think if was absolutely obvious that it was homework but more like a student not understanding something taught in class. and i had a question related to this, so i answered the OP with this (as far as i know he/she has seen where the thread moved to):

sorry, kidia. they moved the thread but they didn't leave a little "moved" arrow behind.

for monatomic gases (He Ne Ar, the inert gasses), each molecule is a single atom and virtually all of the mass of the molecule is concentrated at the nucleus. they're a simple ball with the mass all concentrated at the center. even if you were to spin the ball, there would be very little rotational kinetic energy in that spin because the mass is all at the center. no moment of inertia. so these molecules have 3 degrees of freedom of translation, and only those three. up-down (z-axis), left-right (x-axis), and forward-backward (y-axis). no rotation or vibration.

diatomic gasses (O2 N2) have two identical atoms bonded together. for each atom, the mass is concetrated at the nucleus. so this structure is like a dumbell structure. besides the 3 translational motions (x, y, z-axis) that the monatomic gasses have, there are 2 more rotational degrees of freedom. imagine the dumbell lined up on the z-axis. there would be a non-zero moment of inertia along the x-axis and along the y-axis, but not along the z-axis.

it's obvious (due to symmetry) why the 3 translational degrees of freedom should be the same (contain the same average kinetic energy) and why the 2 identical rotational degrees of freedom contain the same average kinetic energy, but someone else will have to explain why the 2 rotational degrees of freedom contain the same amount of average kinetic energy per degree of freedom as the 3 translational degrees of freedom. can a real physicist explain that?

7. Sep 20, 2005

### ZapperZ

Staff Emeritus
Huh?

So why in the world are you continuing to answer the question HERE, in this thread, of all places? Are you not able to drag yourself to the Homework section and continue the thread that was moved there?

Zz.

8. Sep 20, 2005

### rbj

because it ain't homework, Z. i'm within $\epsilon$ of ending my 5th decade and am not doing homework for any class anywhere. this is simply a question regarding "General Physics" which i think is the heading of this forum.

and no one has, to date, answered the question in the homework forum.

Last edited: Sep 20, 2005
9. Sep 21, 2005

### ZapperZ

Staff Emeritus
It doesn't matter! The Sticky here says that all HW and HOMEWORK-TYPE, school-type question should go there. So guess where this thing is moving to?

Zz.

10. Sep 21, 2005

### Tom Mattson

Staff Emeritus
OK, let's all take it easy.

rbj, first let me thank you for your efforts to help people with their homework here at PF. We really appreciate it.

On to business: We've decided to move homework threads from the math and physics sections without redirects. I know it makes them more difficult to find, but the idea is that homework threads clutter the front page of a subforum, and leaving a redirect only defeats the purpose of un-cluttering it. Forum leaders are clearly identified and there is a Private Message system which is available in case of confusion.

I would also like to point out that there are Sticky notices at the top of the Physics and Math sections that state that homework is not to be placed there. It should come as no surprise when homework threads are moved to the Homework section, which is at the very top of this site.

If in the future our shuffling things around ever causes you trouble in locating a thread in which you have posted, you can easily find it by going to your user profile and searching (with one click) for all the posts you have made. Those posts will be displayed with links, and you can go back to the thread with a single click.

That said, this really doesn't belong in either Homework or Physics, but rather in Feedback. So, I'm sending it there. With a redirect.

Last edited: Sep 21, 2005
11. Sep 21, 2005

### Moonbear

Staff Emeritus
You said you were answering someone else's homework/coursework question, so why are you getting your feathers ruffled about having to reply to them in the homework help forum? Aside from just homework problems, anything that is coursework related (i.e., questions that come up while studying for an exam, or material that is confusing when reviewing class notes) should be asked in the homework help section. There are not one, but two stickies in the General Physics forum indicating this.

If you're creating new threads to answer the question, how does that help the OP find the answer?

12. Sep 21, 2005

### Bystander

Chemi(stry/cal)forums.com (now The Chemical Forum) opened a couple years back --- got into a housekeeping dither moving threads to "appropriate" sections within the forum --- to the point it became impossible to follow. Someone might try corresponding with them regarding obsessive-compulsive anal-retentive approaches to enforcement of posting guidelines and the net effect it will eventually have on PF.

rbj ---
Might as well address your question: the number of degrees of freedom iin a molecule is 3N. The contributions of those degrees of freedom to heat capacity is, in the gas phase, 3 translational, 2 for linear and 3 for nonlinear rotational, and the remainder are vibrational or internal rotations, see "equipartition principle." You managed to mix heat capacities with degrees of freedom --- no big deal, but in the interest of "homework help," it's a little more desirable to either refresh the foggy memories from the past, or to abstain from posting.

Forum growth over the past couple years has resulted in a sufficient increase in work load that Greg B. has added "mentors" at a rate greater than anyone's ability to really examine the "people skills" necessary for such jobs. As a result, a forum policy that homework not be done for students has "morphed" into a DMV-type fetish for procedures.

Yeah, the redirects are PITAs --- same time, there shouldn't be that many threads that leave the first page w'out resolution. Average is what? Ten posts? Not like the endless wrangling in the philosophy area.

Given that half the posts in Chemistry are "homework," and aren't moved, I'd have to say the policy ain't being applied consistently, and ditching the redirects, nuisances that they are, adds to the confusion. Problem? Yeah --- start moving posts at the whims of a couple dozen moderators, and chaos is just over the next hill --- you aren't going to find two, let alone all, of the staff agreeing on appropriate places for every post.

When credentials blind one to the idea that ALL questions re. physics are "HOMEWORK," one might do well to back up and rethink the quality of one's grasp of physics. The policy originated from the frequency with which students were posting threads titled "Help!" and indicating that they'd left homework until midnight Sunday and would someone please do it for them. The answer was usually "No, but here are some hints." This was formally stated and the homework forums split out for that purpose --- not for ego trips over requests for information.

Greg's got a pretty decent site set up here. Tom's busted his behind on it, and it's reached the "Too many cooks" stage. Time for a buncha people to get over themselves.

How many posts to answer rbj's question? How many posts if we turn off the egos, unstuff the shirts, and tend to the business Greg set things up to handle?

13. Sep 21, 2005

### ZapperZ

Staff Emeritus
Unlike the Chemistry section where there is just ONE, the physics section is a JUMBLE of a number of subforum. You are comparing apples and monkeys here. The chem section, due to a lower volume of traffic, does and appropriately allow homework-type questions. I see nothing wrong with that. This is the VERY thing you are asking for - the flexibility when the purpose and aim warrants it! However, this does not apply to the physics sub-forum and one can easily see why.

And when it comes down to this, it is a JUDGEMENT call on when to move and not to move a physics posting to the HW section. If they were to stay there, then why bother having it in the first place? Keep PF they way it was before. If moving such things creates the apocalyptic scenario that you are describing, I'm sure we'll change it. So far, I don't see that happening.

Zz.

14. Sep 21, 2005

### Moonbear

Staff Emeritus
Like chemistry, we take the biology homework questions in biology too. This is also a practical issue. Due to the volume of physics and math homework questions (to be expected on a site named "Physics Forums), the few biology or chemistry questions we get would be quickly lost amidst the flood of physics and math homework questions (of which many similar questions are posted, so keeping them all in one place and guiding the students over there might be helpful for another student to see how similar problems were addressed). We don't have a huge amount of traffic in biology, so it's not distracting from other discussions to answer some homework/study questions in between.

Though, ZZ, with all due respect, your sticky thread title is a tad off-putting. I'm concerned it might scare away some students to see a thread that sounds like it's saying, "Don't Ask About Homework Here!" Most people will see something like that and just leave without even reading further to see you meant, "But you should post over there." People, in general, tend to respond better when given instructions as a positive...do this, or do that...rather than as a negative...don't do this or that. It's likely to get better compliance as well. Perhaps you could change your thread title to convey the important message, which is, "Homework questions should be posted in the homework help forums."

15. Sep 21, 2005

### ZapperZ

Staff Emeritus
You're probably correct. I shouldn't have made the posting after having to move at least a dozen clearly-homework questions. I find it highly puzzling (and annoying too) on why people skip the first 2 lines on the PF list of forums that clearly had the word "Homework" in them and zeroed in right into the main physics section.

I'll edit it when I find the right "words", or maybe Doc Al can make it sound a bit more "diplomatic". Note that I didn't intend it to be a sticky. It was originally just an ordinary posting.

Zz.

16. Sep 21, 2005

### Moonbear

Staff Emeritus
If you land here via a google search or some other means, you might not start from the main page with the full forum list. When I first found the site, I think it was the relativity forum I landed in and had no idea how much more there was to the site for a while...I wasn't used to navigating forums with so many subforums.

You should have written it before you went to Disney. You're always in a much better mood before you go than after you return...which is rather backward from how most people are before vs after a vacation. :rofl:

17. Sep 22, 2005

### Bystander

Missed the point; if Ian and Monique start moving HW from Chem., Bio., and Earth, and thermo questions start moving from engineering, Chem., Bio., and Earth to Cl. Phys., and other mods start moving ALL inappropriately located posts, things can get hectic quickly. Don't recall the history of rbj's response to the OP for the case under discussion, but I do recall noticing the post, and wondering where the hell it went some time later.

Re. "judgement calls:" once a post has gathered responses, movement of that post without pointers is an extremely rude thing to be doing to people who are participating in the thread, and to people who may be following out of idle curiosity or serious interest.

Not really --- please explain what qualities of the "jumble" require inflexible application of posting guidelines --- I'm missing something that definitely annoys you on this point, and given that "it's all physics, even the stamp collecting," what I see is the usual human failure of two or more people to be able to sort n objects into m categories the same way; there is obviously another factor beyond the difference between Dewey Decimal and LOC, or Chicago A and Turabian, that I'm not picking up from your explanations so far. Were I moderating it would peeve me no end to be constantly dealing with students misplacing HW; I'm not, and it still peeves me no end. That's the way students are --- "My problem is your problem, and I want you to deal with it immediately, and I don't have time to pay attention to any requests on your part that might make it easier for you to help me." I doubt that requests of the regular membership that they refrain from replying to obvious homework questions until the mods have time to move them would be any more successful.
Derivation of the equipartition principle ain't homework in the sense that I ever assign students to turn in a meticulously hand-written work on multiplying N by 3, subtracting 3, subtracting 2 or 3, and telling me how many vibrational and internal rotational modes a molecule might have --- it might be supplemental study, handwaving discussion in a text or in class, or one of those "divine revelations" from class notes for which a student is seeking a little more substantial discussion to aid in understanding.

"Apocalyptic?" I said "chaotic." People ain't gonna come back after the second or third Easter egg hunt --- just something to consider when making the "Judgement Calls" --- "How many people is this move going to inconvenience?"

18. Sep 22, 2005

### ZapperZ

Staff Emeritus
Er.... INFLEXIBLE?

These threads were never moved, and one can easily argued that they also constitutued homework-type problems:

and etc!

You seem to think that I gleefully just move stuff irrationally without even any consideration on anything. If this is the kind of monster you think I am, there's nothing I can do about it. However, this is what I said as a judgement call, and I will bet that a lot of yours could be call under question too.

And I am not the only one moving HW-type questions out of the main forum area without redirects. It is just more obvious from the physics forum because of the frequency. If people think (i) this is not appropriate or (ii) HW posted in the main section should stay there, making the HW section obsolete, then let's do that and clarify our policy. However, to argue that somehow, there is a EASY judgement call like this that you can make, that is just not true.

Zz.

19. Sep 22, 2005

### Tom Mattson

Staff Emeritus
That's mostly my doing. I'm always looking to formalize our procedures so that we minimize the number of subjective judgments that have to be rendered. It may look anal from the outside, but you aren't the one who gets a Private Message from every member who feels that he has been arbitrarily discriminated against. If we have a policy for the actions that we most frequently take, and if we always follow it, then we can refer disgruntled members to that policy and consider the matter settled.

It's not that the homework threads linger for too long, it's that there are too many of them, and that homework questions make for boring discussions. People don't read the Physics section to find out what force is required to push a 10.0 kg mass at 2.5 m/s2. They read it in the hopes of finding topics that are worthy of discussion. That is what I consider the spirit of the ban on homework threads from the Physics and Math section. Those threads clutter up the board, and moving with a redirect only defeats the purpose, IMO.

Actually, the "homework goes in the homework section" is not a site-wide policy. The Mentors are given the freedom to set rules for their subsections as long as they are consistent with the PF Guidelines stuck to the top of the Feedback Forum. If Monique and Ian want to allow homework in Chemistry, then there's nothing in the policies of PF that forbid it. And with the lower volume of posts in Chemistry, I wouldn't think that it would be too much of a problem.

And I am not convinced that the chaos that you predict (as a result of moving threads around) is going to come to pass. vBulletin is a widely used Forum platform, and the longer it is "out there" the more people will become used to its features. In time people will learn to subscribe to threads or search for their own posts/threads or to use the search feature. Moved threads are not difficult to locate.

Finally, nothing here is done at the whim of any moderator. Our policies are scrutinized, deliberated over, and decided by consensus. Once that happens, we make every attempt to consistently apply them.

Heh. I actually think that we could use even more help. I don't know how Kerrie and Hypnagogue handle Philosophy between the two of them, and I certainly don't know how Evo handles the Wild Wild West all by herself. But they aren't complaining, so I guess everything is OK.

20. Sep 22, 2005

### Lisa!

Once 1 of the mentors moved my thread to other sciences forum. It was about earth but I wanted to know more about gravitation's affect on mountain's height not mountain itself. So I think using PM system is really neccessary sometimes!
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I think you'd better to move part of this thread to HW forum, another part to staff forum.
Is there any warning for those who interfere to Mentor's job?:uhh: