Physical Definition and 1000 Threads

Homework Statement The question states: "Which of following changes that affect the composition of our atmosphere involve physical changes and which involve chemical reactions?" Then the question lists 6 different scenarios and I have to sort them into either "chemical reaction" or "physical...

This is not homework related and I am having some trouble with describing a part of a system. It is a Rube Goldberg machine. I have two vertical "levers" with axles in the middle of them. I'll post photos. I am really having trouble describing them more or less because I don't know what a good...

After some reading, I'm quite confused about the vacuum state in interacting QFT. I've read the @A. Neumaier post on "The Vacuum Fluctuation Myth," where he notes that "bare quantum field theory with a cutoff, the vacuum is a complicated multiparticle state depending on the cutoff – though in a...

I have found that some people say “yes, definitely”, and other days “no, definitely not”. Those who say “no” seem to regard PLA as merely a neat way of packaging the equations. Those who say “yes” seem to regard PLA as somehow fundamental. (There have actually been two recent books on this...

So I have been reading '2D Topological Quantum Field Theory and Frobenius Algebras' by Joachim Kock recently and I couldn't help but wonder, how is this related to physics? I'm currently in the first chapter and he defined a TQFT as a monoidal functor. Now this seems somewhat abstract (which I...

Can we truly have a rest frame or should it be a close to rest frame? Even if I'm stationary and sitting on my porch and the observer in the car passing is moving, I'm still not at 0 velocity. The Earth is moving at 67,000 mph and the galaxy is moving at 250,000 mph. I'm never in a single...

A common use of the Fourier transform in physics is to transform between momentum-space and position-space. But what physical variables am I allowed to transform between? For instance can I use the Fourier transform to go from momentum space to frequency space or whatever?

My question is whether there is a lowest possible probability for something to possibly (physically) occur on a cosmic basis? That is, is there a threshold 'lowest' probability below which something cannot occur? I'm not referring to 'zero' as the lowest probability. That's obvious. Rather, a...

Hello! I have a question about the first problem in Stat Mech (Physical Adsorption) from http://web.mit.edu/physics/current/graduate/exams/gen2_F01.pdf. The solution to it can be found http://web.mit.edu/physics/current/graduate/exams/gen2sol_F01.pdf. I understand the logic they use for the...

Hello everyone. I'm a writer who is currently working on a Sci-fi novel that deals heavily with military combat. During one scene in this novel there's squad leader who sustains a sever chest injury which causes several parts of her rib cage to break. Now, this squad leader insists on...

Hi, I need more memory (not to much though... 50GB should be fine for now), but I don't know whether to buy an external hard drive or try cloud storage. I'm pretty dumb when it comes to computers and related stuff so I'd like to hear some suggestions. Thanks Ric

hi guys i recently was reading about hawking radiation and how he overcome the lack of a theory for quantum gravity by using a mathematical trick ( to see the effect of gravity on quantum fields ) and this trick was the Bogoliubov transformation ... , i just want some one to briefly explain...

I have to sit an exam on non linear dynamical systems in a couple of weeks. Something that's been asked in the past is to name physical examples of different types of bifurcation. I've consulted Strogatz's book and the internet to try and find some, but I can't seem to find many (or even any)...

Do string theory’s compactified dimensions have a predicted physical interpretation? Do they for example represent the space/planes/domains in which a string ‘lives’? That is, the local permissible evolution space of a given string?IH

I want to create a small pad consisting of two electromagnets that repel and attract each other, this can give the feeling that something is pushing up against your skin if held. Is this a practical idea?

I am extremely confused by the use of the term coefficient of increase of something. For example , if it is stated that the index of refraction varies linearly with a coefficient of 2.5×10^-5, how is this coefficient defined? Is it simply the slope of the line plotted with index of refraction on...

Hi there I am a high school science teacher and I want to present my senior classes with a model of the fundamentals of the physical world to serve as a mind map for us when we reach each topic. I have started by creating the one below and then realized I may have left off momentum...is momentum...

Do you know any website where I can find chemical and physical properties of common substance (heat capacity, enthalpy of formation, boiling point ecc...)? Thanks Ric

This came up in another thread. GR more or less follows directly from Lovelock's Theorem. You simply assume the metric has a Lagrangian. Where does that leave other things like the Equivalence principle? Thanks Bill

I derived a relationship between frequency and tension of a string, accounting for tension's effect in the linear density of the string. So in a nutshell, the equation is more complicated and is in the form of f^2=aT^2+bT (f is frequency, T is tension, ab are constants involving the control...

Homework Statement The picture illustrates a simple pendulum and and two physical pendulums ,all having the same length ,L. Class their period in ascending order. Homework Equations T = 2π / ( I/mgh) I = Icm + mh2 Icm=(ML2/12) The Attempt at a Solution I have found the period for first...

Hi guys, i'm a computer scientist with no background in Chemistry and I'm very interested in the field of Physical Chemistry. Do you think i can directly start to study a Physical Chemistry book ? If yes, do you have some books to suggest ?

From the above description of Virtual displacement, what I understood is: virtual displacement is another name for ## dx_i ## when dt = 0. I didn’t understand its physical interpretation. Could anyone please put some more light upon it?

I'm trying to understand renormalisation properly, however, I've run into a few stumbling blocks. To set the scene, I've been reading Matthew Schwartz's "Quantum Field Theory & the Standard Model", in particular the section on mass renormalisation in QED. As I understand it, in order to tame the...

Homework Statement Homework Equations T = sqrt(mgL/I) The Attempt at a Solution my calculated Inertia (I) = 1/3(m/2)L^2 + (m/2)L^2 my distance (d) = L/2 m is just total mass so, T = 2pi * sqrt(mgd/I) = 2pi sqrt(4L/(3g)) which is wrong :(

Hi I would like to know if there is any physical or medical scientific tests I can take to know/confirm my energy levels/body energy levels and will level when it comes to motivation. the reason for wanting to take these tests is that I have a severe mental brain neurological disability known...

For example, Lorenz transformation of time means That measurement of time changes from one observer to another. I have read that this means moving clocks run slower. But this can't be true because Lorenz transformation of time depends on both of the seed of the observer and the object he...

Hi, I have read some on the PDEs for fluids, and particularly for rogue waves, where for instance the extended Dysthe equation and the NLSE look rather intimidating: Take for instance the Non-linear Schrödinger eqn: \begin{equation} \frac{\partial^2 u}{dx^2}-i\frac{\partial d...

Why are the fundamental physical constants called "constants" when they change over time? I've read that the constants were adjusted in 1986. How can there even be something that is constant, when we can't even see the entire universe?

For a traditional circuit simulator, like the free and open source versions of SPICE (i.e. ngspice), it seems to me that they can technically all simulate the same kinds of circuits. Assuming you had a portable SPICE model (either written in SPICE or compiled with ADMS), you could simulate the...

The Hamiltonian of the Qi, Wu, Zhang model is given by(in momentum space): ## H(\vec{k})=(sink_x) \sigma_{x}+(sink_y) \sigma_{y}+(m+cosk_x+cosk_y)\sigma_{z} ## . What is the physical meaning of each component of this Hamiltonian? Note: for the real space Hamiltonian(where maybe the analysis of...

I see that this has been discussed before, but the old threads are closed. As Carl Brans and others note, it seems too big a coincidence to ignore. Why is exotic smoothness "good" (in the sense that it permits richer physics or something like that)? Exotic Smoothness and Physics,arXiv "there...

I want some undergraduate level (or postgraduate level will also do) books on physical chemistry. I've got two books: one by Ira Levine and the other by Peter Atkins. But both these books contain only huge amounts of thermodynamics. Other topics are almost not touched upon. I want a book that...

What is the difference between physical chemistry and chemical physics?

Hey guys, I was wondering if algebra based physics will be useful or I will be in a disadvantage? I’m doing a minor in chemsitry and math. So I’m not sure when I will take PCHEM. Probably after partial differential equations I will take it. I’m hoping to take it in fall 2019 or spring 2020.im a...

What does it means for a physical theory to have hamiltonian, if it is formulated in lagrangian form? Why doesn't someone just apply the lagrangian transformation to the theory, and therefore its hamiltonian is automatically gotten?

Dear physics forums, What is the physical interpretation of imposing the following constrain on a Hamiltonian: Tr(\hat H^2)=2\omega ^2 where \omega is a given constant. I am not very familiar with why is the trace of the hamiltonian there. Thanks in advance, Alex

Could huge amounts of energy change the universe's nature (fundamental physical constants, laws, dimension)? Could it change it so much that it would enable our universe to be a multiverse of level 1, 2, 3 or 4? https://en.wikipedia.org/wiki/Multiverse

Homework Statement We are given that the B-field is: $${\bf{B}} = C \delta(s-R) \hat{\phi}$$ where ##s## is the distance from some object and ##R## is the radius of some object. What kind of physical situation would create such a B-field? Homework Equations Stated above. The Attempt at a...

I am taking the second semester of physical chemsitry (quantum, spectroscopy, and some stat mech). I was wondering if there are any resources outside of the ACS study guide and open course ware. I'd really like some practice tests if possible so I can see what I need to study. Also, any lecture...

Consider the QM postulate which states that physical states are represented by rays in a Hilbert space. Consider a ray ##R##. An observer from other frame will have a correspoding ##R'## which can be either - equal to ##R## or, - not equal to ##R## Suppose the two frames are inertial frames...

1. Homework Statement Question 1: given a rigid tetrahedron, with vertices A, B, C and D anchored to their initial locations with an arbitrary but uniform spring constant, will Cases 1, 2, and 3 below result in the same behavior of the system? - Case 1: a force of constant magnitude (red...

I am encountering this kind of problem in physics. The problem is like this: Some quantity ##A## is identified as a potential field of a ##U(1)## bundle on a space ##M## (usually a torus), because it transforms like this ##{A_j}(p) = {A_i}(p) + id\Lambda (p)## in the intersection between...

I've often wondered at the "resolution" of the human visual system but it's not at all clear from what I've read whether this question even makes sense. As a sort of general position, many of the articles I've read suggest that the human eye, over the full field of vision, delivers around...

Homework Statement For calculating angular frequency of a physical pendulum, I consider its center of mass motion. The COM motion is a simple pendulum motion. Considering a coordinate system whose origin is the pivot point. Then, the COM is the length of the corresponding simple pendulum. Is...

Is it applying mathematics to a phenomena in the real world and create a model, test the implications of that model by manipulating the math, then checking that with observation and other established physical laws. If it doesn't match up, then a new model is required or another type of...

Hi! My name is David. I'm a theoretical physicist from Stuttgart, Germany. Over the past months I have been developing an open source application called Insect, which I hope would be of interest to some of you. Insect is a high-precision scientific calculator that comes with full support for...

Hey guys, Can anyone help me think of some relevant physical (8 or so) and chemical properties (5ish) required by flag poles. I was struggling to think of some but here are some of mine: Physical Flexibility Elasticity Melting point Strength? Electrical conductivity?? Chemical Stability UV...

Homework Statement Please provide a physics explanation of this question: How does load current affect the potential difference across the terminals of a cell? Homework EquationsThe Attempt at a Solution p.d. inversely proportional to current. Thus, when I increase, the p.d. decrease and vice...