# Tagged Questions

Use this for questions relating to the proper use of physics terminology or nomenclature.

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### Difference between a reversible change and a reversible process?

Question In thermodynamics what is the difference between a reversible change and a reversible process? Additional information I am new to the topic of thermodynamics and getting confused about ...
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### Radial excitation and orbital-angular momentum excitation

Sorry. Just want to make sure, but what does radial excitation and orbital-angular excitation mean in the context of bound states? Just higher $n$ and $\ell$ quantum number?
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### Friction force in rolling motion

In rolling without slipping motion we know that the friction acting is static friction and so we treat it as an unknown while solving equations of dynamics. Question: Is the static friction during ...
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### Is there a scientific term for the right-hand-(grip-)rule?

To illustrate and remember the direction of rotation around an axis defined by a vector as it happens to be in some fields of physics, one can employ the right-hand-rule: (image from here) Is ...
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### What is the difference between Chiral anomaly, ABJ anomaly, and Axial anomaly?

I get confuse with these three terms: Chiral anomaly, ABJ anomaly, and Axial anomaly. I can not find standard definition of these three. Is there anyone can describe precisely?
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### Gravitational acceleration

'What is difference between free fall acceleration g and gravitational acceleration a?***a is with subscript g.In my textbook it is written that "free fall acceleration = gravitational acceleration - ...
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### What is primitive divergence?

As in the title, what is primitive divergence? How is it distinguished from normal divergence? As a followup, what is a primitive divergent graph in a theory? Some simple examples?
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### What is a weak solution of the MHD equations?

Many papers concerning solutions to the magnetohydrodynamics (MHD) equations (eg. Osher, 1984) say that one is generally interested in finding weak solutions. Sometimes they are even called global ...
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### What are “correlations”?

When working with realistic two-body hamiltonians, a direct diagonalization is almost always imposible. Thus one usually takes a procedure which yields an approximate solution. A well known approach ...
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### What is the essential difference between a resonance and a particle?

Let me start by explaining my particle physics background is very patchy, so this question may not be as coherent as I would like it to be. In general terms, what is the difference between a ...
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### What is the difference between a “model” and a “theory”?

In my past questions I have used the terms "model" and "theory" interchangeably. So we have statements along the lines of The Standard Model is our best theory of particle physics but I have also ...
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### What does the term 'hyperbolic model' mean?

I am reading this non-linear discrete dynamical system paper. The authors mention the term hyperbolic model. What does that mean?
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### “Complete” confusion

The word "complete" seems to be used in several distinct ways. Perhaps my confusion is as much linguistic as mathematical? A basis, by definition, spans the space; some books call this "complete" -- ...
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### What is meant by “the superpotential is not renormalized”?

Reading about supersymmetry I often read the phrase because of the non-renormalization theorems the superpotential is not renormalized. I would like someone to be more explicit on what is ...
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### Is there a name for the squared refractive index?

In studying wave propagation through multilayers, the squared refractive index $n^2$ is a more pertinent parameter than $n$ itself. Is there a received name for $n^2$? Of course, as long as there is ...
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### Is a “shift in the meaning” of Accuracy and Precision occurring?

Accuracy and precision are among the most fundamental concepts in experimental physics, and, I always believed, completely unambiguous. Recently I found that the Wikipedia article on Accuracy and ...
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### Is there a name for the linear quantity corresponding to the (quadratic) “interval $\Delta s^2$”?

Recently it has been affirmed here (again) that the quantity called "interval (also 'spacetime interval' or 'invariant interval')" is referring to two (in general distinct) events as arguments, such ...
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### Is 'Boltzon' an accepted name for particles following Maxwell-Boltzmann (MB) statistics?

In my curriculum during one of my statistical mechanics visiting lecture classes, our teacher was referring comparatively macro particles following MB statistics as "Boltzon". But I have searched ...
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### Why can't we precisely define physics? [closed]

While reading a textbook, I came across this statement: "A precise definition of physics is neither possible nor necessary." I was curious why it is not possible but the textbook never ...
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### What is the difference between air pressure and atmospheric pressure?

I know that air pressure and temperature are inversely proportional. Now I saw in a book that "Atmospheric pressure decreases as we go higher and higher." But at greater heights the temperature ...
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### Motion in oscillating field: expanding in powers of $\xi$ [closed]

I'm reading an excerpt from Landau/Lifschitz's Mechanics book about motion in oscillating fields. Two equations for the motion of a particle with mass $m$ are set out: m\ddot{x} = ...
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### Does “finite” include zero?

Infinity, is clearly not finite. But there is some dissent on whether or not zero is finite. I have seen authors use "finite" to indicate the value of $0$ is excluded as well as infinity. Is there ...
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### What do physicists mean with “classical critical behaviour”?

What do physicists mean with "classical critical behaviour"? As far as I am concerned it should be "power law behaviour" of some quantity close to the critical point but I ask here to be sure.
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### Can someone explain what's the difference between all these terms in “Simple Words” with their “applications”? [closed]

I'm very confused between all these terms. Can someone explain what's the difference between Classical Mechanics, Relativistic Mechanics, Quantum Mechanics, Quantum Field Theory, ...
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### Object moving with 2 linear accelerations

Say I have an object moving with an acceleration of 5 m/s$^2$. At a certain point X, due to some forces, the acceleration of the object changes from 5 m/s$^2$ to 2 m/s$^2$. Would this change in ...
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### What does “Standard Model” really refer to?

I am reading the arXiv published paper by Frank Wilczek called "Physics in 100 Years". Apparently, this paper is the printed form of a talk given at Brown University earlier this year (2015). Right ...
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### Simple explanation of Coherent integration radar

I have a physics background, and I'm reading some physics data analysis papers where they keep throwing around the term coherent integration. I've done the google search, but the best answer I could ...
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I read the term field gradient in most of the article about magnetic field. I search it online but most of the explanation is about the math. I wonder in physics, what the gradient field really mean? ...
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### Can anybody explain about phase shift and phase spectrum terms in case of multidimensional signal?

I know about phase of a 1D signal, but when I move into higher dimensions like 2D or 3D etc, it becomes headache to grasp the concept. What do the terms "phase shift" and "phase spectrum" mean in ...
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### What is nuclide notation referring to? Only the nucleus or the whole atom?

sorry that this is an easy question but I am just a bit confused about nuclide notation. When you say e.g. $^{240}_{94}\text{Pu}$, are you referring to the atom of $\text{Pu}$ or only its nucleus? It ...
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### Does graphene have a honeycomb lattice?

In my grand ignorance I would state that graphene has a honeycomb lattice. Some tend to agree with me and some others do not. I'm curious to know what members of the SE community think is the right ...
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### Square-Cube Law?

I've heard about something called the square-cube law. What is it? All I know of it is that it has something to do with mass of large objects and their gravitational influence.
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### What does “interact via strong force” mean?

I was just wondering if the words "strong force" and "strong interaction" are interchangeable? Also, these are referring to "strong nuclear force", correct? Then what does it mean for particles to ...
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### Should it be obvious that independent quantum states are composed by taking the tensor product?

My text introduces multi-quibt quantum states with the example of a state that can be "factored" into two (non-entangled) substates. It then goes on to suggest that it should be obvious1 that the ...
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### What is space charge and how to calculate it?

I want to clarify the meaning of space charge. What I know is that the space charge is the total charge in a small region in space. I really confuse this in the ion beam context. Many text book says ...
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### Making sense out of covariance and contravariance

I just read about co- and contravariant vectors and I am not sure that I got it right: If we imagine that we have a n-dimensional manifold $M$ then a tangent space is spanned by the vectors ...
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### Why does one call $B$ the magnetic induction?

When one studies electrostatics we have the electric field $\mathbf{E}$. This object usually is introduced as a field produced by a configuration of charges such that the force on another charge $Q$ ...
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### What is third cosmic velocity?

I have been studying Gravitation chapter and there I found one term : Third cosmic velocity which is also known as interstellar speed. So what is it ? What it really tells about? I tried to gather ...
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### What's the difference between “Ohmic dissipation”, “Joule heating”, “ion drag” and “resistive heating”?

The following terms are sometimes used to refer to ... more or less ... the same thing by different people and in different contexts (electronic circuits vs. plasma physics, etc.): Ohmic ...