Discussion Definition and 284 Threads

The region of the ionosphere with highest electron density is where molecules and atoms are being ionized by photons radiated directly from the Sun. Is the rest of the ionosphere staying ionized mainly due to interactions with the free electrons and recombination photons that spread out from...

Hello people, I'm really interested in non-mainstream physics but so far i can't find a place./forum where i can discuss or share theories. I've tried doing it in the Quantum Physics section, but my thread was rejected because personal theory developments are not allowed here. So far it's ok...

Has there ever been an attempt to organize a PF meeting or convention? Personally, I think that would be a great thing for everyone to be able to meet the people they talk to here, if they don't already know them. Obviously, though, there are some immediate issues such as the worldwide PF...

The geography of Great Lakes Earth, and the questions that come with it. Pangaea From 250 to 200 million years ago, all the continents had joined together to form a singular landmass called Pangaea. The brown lines presented in the map are mountain ranges varying in height above sea level...

I simulated an incompressible turbulent flow across a tube. I managed to solve it using OpenFoam and the results seem to be right. However, I noted some vacuum pressure after the sudden expansion but can't figure out why the pressure decreases and then increases again. According to Bernoulli's...

Good day all, I am looking to discuss how to manipulate the magnetic flux of a coil. I unfortunately lack the math skills to calculate what I actually need to build for my project. I have been coop up in my garage trying to physically solve the problem but I am running out of time and money for...

I've read Sir Arthur C Clerk's space odyssey series and curious of the propulsion technologies used in those ships. Ships like Universe and Galaxy of space odyssey 2061 use just water. The fiction speaks of "muon propulsion" too. The main spacecraft s that we see in his 'space odyssey' series...

I was reading through the early chapters of Ross' book on analysis in the section covering the completeness axiom. See below. Followed by a few examples. I'm confused as to why in the example (e), the set does not have a minimum. I can understand that it does not have a maximum, but it...

at firs i apologize if this is not the place for this but really i have exam after few hours and i need chech my solutions . i have some essay questions and i want to check my ideas 1) can we use the diode as switch instead of transistor ?? 2)design an op amp to amplify the dc signal 3)how to...

Hi guys, I am doing a quick survey here. I am not sure this is appropriate in this section but here it is. If your are an engineering students, could you guys please comment on: 1) Who do you ask when you stuck on study-related questions (eg. lecture note, tutorial, assignment questions...

Hi everyone, I have a question (or three) regarding Purcell's discussion of image charges, in pg 137-139 of the third edition of his EM book. He goes over the classic image charge example: a plane held at zero potential, and a charge Q a distance h above it. I'm fine with everything he...

What is not one of those fields? As long as a significant fraction of the population would agree to a law that bans atoms, ... [split from this thread: https://www.physicsforums.com/threads/stunning-reversal-in-sweden-re-nuclear.875103/ ]

am reading Sean Carroll's pop-science book 'From Eternity to Here' and am having trouble connecting the links in his discussion of the Holographic Principle. At the outset, I would ask that you try to answer in terms of Carroll's discussion and without moving into concepts much more advanced...

I was wondering if there was anyone comfortable enough about basic to advanced linear algebra concepts who would be willing to participate in a chat/whiteboard based platform to discuss or answer questions concerning such concepts. I need clarification on a few things

Hi everybody I am a scientific enthusiast with great interest in the renewable energy field. and I had this idea in my head for so many years which i got from a scientific experiment I saw a few years ago. After few years of grappling with this idea in my head I was able to put it into a...

Discussing scientific matters with people who've no background in science presents many challenges and have been discussed on this forum many times throughout the past. Helpful resources do exist. For example, @Ryan_m_b posted a great link a few years ago that gives some general guidelines on...

Here's the idea of this thread. I start by posting a conundrum. It is basically this: if you push the button, something good will happen but at a price. The next poster then says whether he pushes the button or not and posts his own dilemma of the same kind. So let me start with the classic...

I was wondering if many members liked the lord of the rings and also it is hard to find people who like to talk about it in person so I thought this could be a place to discuss it anyway.

Hi there, we are having a tough discussion among friends concerning this topic: Imagine you are inside your car, stopped in the road. There is no obstacles in front of you, just plain road. Suddenly, because of the sound coming from the back, you realize another vehicle is going to impact you...

Mod note: After merging posts from a duplicate thread, the time stamps put the posts in the incorrect order. The original question was, Field strengths aren't measured in joules, so I don't think your question can be answered. PS If your name isn't "Brian Green" you might find another one...

If you really think about these they are mind-boggling.1. Roads. I can get in my car right now and go pretty much anywhere. There is an unbroken route from where my car is parked to virtually every location on this continent. And if I can’t get there by car, there are often specific places to...

A brilliant student, Jonathan sailed through grade school. He completed his assignments easily and routinely earned As. Jonathan puzzled over why some of his classmates struggled, and his parents told him he had a special gift. In the seventh grade, however, Jonathan suddenly lost interest in...

I am trying to understand a discussion of field extensions by Dummit and Foote: Abstract Algebra, page 512 ... The relevant text is as follows:When I first read the second paragraph, starting "Given any field F and any polynomial p(x) \in F[x] ... ... ... ", I thought that D&F were trying to...

Hi I have a really weird idea that is robbing me of my sleep. One of the many problems with fusion seems to be how to harvest the energy released by the reaction efficiently. So as I was slowly drifting into sleep I was wondering, how we usually harvest energy from reactions, and the piston...

Homework Statement (-64)^(3/2) Homework Equations None. The Attempt at a Solution There is no answer that can be reached and it is supposed not be a real number. I was wondering why that is. How is it that there is no "real" answer to this problem?

This is a thread dedicated to the discussion of 0% penalties being applied to late submission, should this be implemented or not? I am a student, and believe that 0% penalties being applied for late submissions is quite frankly ridiculous. At my university in the student assessment and...

Is there a thread at PF devoted to discussing movies? If not, let me designate this one! :smile: What recent movies have you seen or want to see? What did you like or dislike about them? ...Feel free to post anything movies-related that could be fun, interesting, or helpful! Huge chess...

klotza submitted a new PF Insights post A Hand-Wavy Discussion of the Planck Length Continue reading the Original PF Insights Post.

i have read many of the answers and explanations about the similarities and differences between laplace and Fourier transform. Laplace can be used to analyze unstable systems. Fourier is a subset of laplace. Some signals have Fourier but laplace is not defined , for instance cosine or sine...

Does anyone happen to know a website where you can start a discussion with e.g. your colleagues about a very wide, unspecified topic or personal topic (e.g. research proposal which has not yet been decided), but which could still be documented and viewed publicly? I hope I am posting in the...

Hello there...as the title says, when the time of the upgrade comes..lets discuss in this topic problems and other stuff on this new software edit: when i received my notification i was asked to give my e-mail until the upgrade day unfortunately i pressed the X button and i missed to give my...

I am reading John Fraleigh's book, A First Course in Abstract Algebra. I am at present reading Section 22: Rings of Polynomials. I need some help with an aspect of Fraleigh's discussion of "solving a polynomial equation" or "finding a zero of a polynomial" ... The relevant text in Fraleigh...

So nuclear experts out there tell me does this deal make it very difficult for Iran to make the bomb?

An interesting discussion at this conference here: http://physics.princeton.edu/cmb50/videos/20150612_session6_2.mp4 David Spergel said the next project should be to look for something called f and L or is is FNL? Can someone explain what this is and what its significance is? What did you guys...

<<Mentor note: This thread has been split from this thread due to going a bit off-topic.>> I would actually disagree with this. Any tensor has well defined units, but its components may not have the same units as the tensor basis may consist of basis tensors with different units. For example...

Why should I closed the discussion "material for sealing"??

There is a lot of talk about going to Mars. But not a lot of talk about how to keep the people alive on Mars. I am hoping we can talk about that here.

I have reopened the General Discussion classics thread to see if you want to suggest threads to be included or just let it go away (unsticky it). https://www.physicsforums.com/threads/general-discussion-classics.42220/

@dlgoff and I attended a panel discussion at the WI Science Festival. @dlgoff found the video for it and I thought I'd formally share it because it was quite interesting and a very important topic. The general point is that scientists need social and speaking skills. Being able to effectively...

The game is to guess what Feynman and Dirac are discussing. I guess Feynman is explaining his principles of quantum mechanics. "... see Paul, I have come up with three simple principles which capture the essence of quantum mechanics ... a) The probability of an event in an ideal experiment is...

Decided we should have a thread for pre/post launch discussion of the orion capsule. Maybe we can talk about how much we hate wind, or maybe how much we dislike sailboats. Live stream is here: www.ustream.tv/nasahdtv Also a more active discussion over on reddit(sorted by new)...

Homework Statement What would be the effect of calculated value if: a. Jockey weight is in error by 1 g? b. Distance from vane center to pivot point is in error by 1 mm? c. diameter of nozzle 0.1mm different from actual nozzle diameter. Homework EquationsThe Attempt at a Solution as the error...

So we know that there can be no space without time but can there be time without space? I want to ask here because I don't trust yahoo answers :) I put it in bold because I want to know if it's possible, not if it's likely or anything, just if it could be possible, Thanks.

If you were limited to only using a single mouse trap and cheap raw materials from a local craft store, how would you design a "mouse trap car" to pull a mass of 200g (soda can w/mass)? I'm looking to maximize the mouse traps distance traveled and speed. I'm looking to minimize the weight...

I was working on trying to find the short circuit current rating of a 120 volt panel fed from a 7.5KVA transformer. Using P=IV you get 7.5KVA=120 * I I = 62.5 Amps. Then I believe you divide that current by the impedance of the transformer. .03 is the impedance in this case in the...

We need a general thread to talk about all the matches. So here it is! Let's keep the discussion rolling during the matches too for those who are watching. If you are interested in joining the PF World Cup Futbol League go here: https://www.physicsforums.com/showthread.php?t=756611 First...

Hi, I was thinking of something: How are one supposed to calculate the moment needed for a scoop to scoop up a sample of e.g. sand? Does the classical p=mv work? Any ideas or comments?

Before I get down to business, I would like to note (you don't have to read this; feel free to skip to where it says "here are my questions") the following: ------------- Firstly, I am somewhat still new to posting in these forums, and as such, am not sure if this is the right place to put this...

Hello everyone! I would first like to say that I am not exactly unfamiliar with these forums; I'm one of those people who is like a... "long -time thread watcher, first time poster." So yes, this is my first post. :smile: I have used these forums as a sort of reference library, looking up...

A person is inside a car. This person is not using the seat belt. The car crashes with a solid wall and decelerates quickly. The person, due to inertia, keeps moving until stopped by the wind shield. I want to analyze the movement of this person after the crash, but I am troubled...