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

learn more… | top users | synonyms (1)

0
votes
2answers
44 views

On Elementary Particles

The mass of positron and electron are same. Also their charges are equal in magnitude but opposite in nature. Then why positron is not called one of the elementary particles? Is this only because it ...
0
votes
2answers
28 views

What is the formula of power of an optical instrument?

I have searched and found that the power of a lens, with surrounding medium of refractive index $n$, is $n/f$ where $f$ is the focal length, the formula is $$n/f=(n'-n)/R1 + (n-n')/R2.$$ But in my ...
2
votes
2answers
163 views

What exactly is meant by saying that two events had been “simultaneous in an inertial frame”?

In order to address my question based on a concrete example setup let the following two separate events be given: participants $A$ and $J$ encountering each other in passing (additional participants ...
0
votes
1answer
46 views

Lorentz invariance vs. covariance

I am a bit confused whether relativistic theory is Lorentz invariant or covariant. And please explain why?
1
vote
0answers
41 views

How to get from $E_8 \rightarrow E_7 \rightarrow E_6 \rightarrow …$

I read in section 2 of this paper : "There is a well-defined chain to descent from $E_8$ to smaller groups by chopping off a node of the Dynkin diagram." What exactly is here referring to ...
1
vote
1answer
122 views

Vorticity versus Viscosity

For a work project I need to revive my aerodynamics knowledge again. Can somebody help me with the distinction between vorticity and viscosity. If a flow vorticity is not equal to zero, the flow is ...
0
votes
1answer
43 views

What is the meaning of “site”?

Reading questions, I have come across a recurring notion of "site". Whilst I am able to understand the questions I am unsure as to what a "site" actually is and to what it corresponds physically. I ...
3
votes
1answer
71 views

Is Kinetic Theory part of Statistical Mechanics?

Some years ago from now I've seem some basic details about what was then called "kinetic theory of gases" where the study of property of gases was made by statistical considerations about the momentum ...
2
votes
2answers
79 views

What unit system does Fahrenheit belong to?

Wikipedia's page for Imperial Units does not list Fahrenheit. The corresponding page for SI Units lists Kelvin as an SI unit, and Celcius as a derived SI unit. This leads me to believe that ...
1
vote
2answers
42 views

What is the difference between the potential $V$ and the effective potential $V_{eff}$?

What is the difference between the potential $V$ and the effective potential $V_{eff}$? Some times when solving problems, an effective potential $V_{eff}$ is defined and its usually equal to the ...
4
votes
4answers
1k views

What is a peryton?

It is a bit hard to find an accessible explanation online. I find the word "peryton" in some papers about radio astronomy, here's one example: http://arxiv.org/abs/1503.05245 I don't think they refer ...
0
votes
0answers
39 views

What is the difference between mass defect and mass deficit?

Is there any difference between the mass defect and the mass deficit? I have read that the mass defect of a nuclide is never negative and have also been told that the mass defect is the same as the ...
1
vote
1answer
44 views

Two-component formalism and four-component formalism [closed]

When deriving the Dirac equation for spin-1/2 particles, we realize that the wave function must be four-component. In some works, people use two-component wave function for calculation. So, my ...
1
vote
1answer
99 views

What is the difference between a parameter, a variable, and an operator in QM?

On the question why time isn't an operator, people will usually say that time is a parameter in QM (Time as a Hermitian operator in QM?) and not a variable. Can someone please distinguish between a ...
5
votes
2answers
91 views

What is a full cycle in damped oscillation?

Maybe it seems a dumb question, but I can't understand what the cycle in a damped oscillation is? Let's take an example: In harmonic motion, one cycle is the smallest distinguishable part of wave ...
1
vote
1answer
88 views

When was the first time that superconducting quasiparticles were called Majorana fermions?

Since a number of years, the field of superconductivity has a growing obsession with Majorana fermions. I wonder how far back we can go: When was the first time that superconducting quasiparticles ...
1
vote
2answers
126 views

How to tell the order of a Feynman diagram?

How can we know the order of a Feynman diagram just from the pictorial representation? Is it the number of vertices divided by 2? For example, I know that electnro-positron annihilaiton is first ...
0
votes
1answer
14 views

What are pressure threshold patches called in professional terminology?

I am making a small combustion chamber, and need to measure the pressure when a combustion occurs. This is a hobby project, so I don't have enough money to buy a dP cell with a remote membrane for ...
0
votes
2answers
46 views

What does it mean to “contract” a tensor identity?

I'm taking a GR course at the moment, completely stumped on this step here: starting from the Bianchi identity: Then it says "Contracting the Bianchi identity..." How does this work and what ...
0
votes
2answers
130 views

Why is static electricity called static?

They called it "static" because "it doesn’t go anywhere". In order to create static electricity, you have to rub two different materials. When you rub them, the electrons move. So, why is it called ...
-9
votes
2answers
61 views

What does the “UV” in “UV completion” stand for? [closed]

What does the "UV" in "UV completion" stand for? Also, I'm not sure which tags I should tag this question with.
3
votes
1answer
5k views

Difference between steady state and equilibrium?

In semiconductor physics, what is the difference between steady state and equilibrium. How analysis of devices varies in these processes?
0
votes
0answers
59 views

The Einstein-Cartan equation as the “living heart of gravity”?

I recently read in A Journey into Gravity by Wheeler that "The Einstein-Cartan equation gives us the most vivid image that mankind has ever won of the living heart of gravity" (P.118) ...
-1
votes
1answer
39 views

What does $\bar{x}_{\textrm{el}}$ represent?

In the context of centroids and moments, what do $\bar{x}_{\textrm{el}}$ and $\bar{y}_{\textrm{el}}$ represent? For example: $$\bar{x}L = \int \bar{x}_{\textrm{el}}dL$$ Some references that use ...
1
vote
1answer
61 views

What is a point transformation?

This problem comes from Goldstein. What does $s=e^{\gamma t}q$ mean? Do I just put $q=e^{-\gamma t}s$ into the Lagrangian? But I don't know what that means. I think the point transformation may ...
3
votes
1answer
60 views

What is the difference between a magnon and a spinon?

For a long time, I thought the terms "magnon" and "spinon" were equivalent, describing the collective spin excitation in a system. Lately, I have seen remarks in the literature that they indeed do ...
0
votes
3answers
152 views

Is my conceptual understanding pertaining to heat & temperature correct?

From what I've understood: Heat is the total sum of translational energy possessed by individual atoms in an object. Temperature is the average translational energy possessed by individual atoms ...
1
vote
1answer
106 views

Difference between a “source dipole” and a “force dipole”

I know quite well what a dipole is and in general what multipole moments are (in the context of, for instance, electrodynamics). What I find myself confused by is something called a "force dipole" in ...
1
vote
3answers
225 views

What is actually a conservation law?

Though in his lectures, Feynman didn't define conservation law, he did use it while explaining divergence theorem: [...] heat is conserved. That is, no heat is generated inside the material and ...
2
votes
5answers
139 views

A reference frame is any coordinate system or just a set of Cartesian axes?

In Physics the idea of a reference frame is one important idea. In many texts I've seem, a reference frame is not defined explicitly, but rather there seems to be one implicit definition that a ...
0
votes
1answer
46 views

Metric in Lagrangian and the minimum total potential energy principle

I was wondering why physical systems "like" to go to the minimum of potential energy and I found this question, that tries to justify the minumum total potential energy principle. I was also reading ...
1
vote
2answers
97 views

What does the “T” stand for in T-duality?

First of all, I am not a physicist. I'm a graduate math student and recently I came across the concept of T-duality. Actually I'm studying generalized complex geometry, which according to this paper ...
4
votes
1answer
86 views

Why “colours” of light are given in wavelength not frequency?

If I understand correctly, when a beam of (monochromatic) light passes through media of different refractive indices, its wavelength changes but frequency remains constant. Why, then, are colours of ...
1
vote
1answer
35 views

Difference between hydrostatic and uniaxial pressure

I'm confused with these two terminologies. Does 'hydrostatic' means every direction while 'uniaxial' means one direction? What're they usually used for?
0
votes
2answers
40 views

Usage of singular or plural SI base units when written in both symbol as well as name [closed]

I have multiple doubts related to the usage of singular or plural SI base units when written in both symbol as well as name. I have framed this question under two parts, namely, Part (a) and Part ...
0
votes
1answer
60 views

What is this equation $f^e = f^a - \nabla U$?

Recently in a mechanics class my prof scribbled down something looked like $$f^e = f^a - \nabla U.$$ Where he claimed $f^e$ is the external force on an object, $f^a$ is the applied force on the ...
1
vote
1answer
35 views

Kinematics and dynamics - what pattern do they portray?

The Equations which are derived for kinematics and dynamics are some patterns related to the body in motion. What is the demarcation in the pattern that kinematic equations and dynamic equations ...
2
votes
1answer
62 views

What is meant by a “stiff” or “soft” equation of state (wrt neutron stars)?

I am currently trying to understand the history of the development of the equations of state and structure of neutron stars. In my textbook, I frequently encounter phrases such as "The ...
0
votes
2answers
85 views

Why isn't the Time-Independent Schrödinger Equation an equation of motion?

I thought an equation of motion was something where you are given a Lagrangian and, using the Euler-Lagrange equation, you then find the equations of motion for that system. Same basic idea for the ...
0
votes
3answers
80 views

Definition of non-degenerate metric tensor

We know that a metric has a property which is called non-degeneracy. I was searching for what does that mean and saw it associated with the fact that $det(g_{\mu\nu})\neq0$. How does this relate to ...
0
votes
1answer
75 views

What is the meaning of phenomenology?

From what I understand, phenomenology as it is used in science means talking about the details of a phenomenon without going deep into the fundamental physical processes that lead to the phenomenon. ...
4
votes
1answer
3k views

What is the difference between the words transparent and translucent?

Merriam Webster defines transparent as: Having the property of transmitting light without appreciable scattering so that bodies lying beyond are seen clearly. And translucent as: ...
5
votes
2answers
9k views

Convective and Diffusive terms in Navier Stokes Equations

My question has 2 parts: I just followed the derivation of Navier Stokes (for Control Volume CFD analysis) and was able to understand most parts. However, the book I use (by Versteeg) does not ...
7
votes
3answers
265 views

Fiducial volume in collider/detector physics

I'm trying to make some sense of ATLAS measurements for a personal project to learn how to use Pythia, and part of my work requires me to recreate the distribution for Z boson decay. I encountered the ...
0
votes
3answers
96 views

What is the difference between maximally entangled and maximally mixed states?

To my understanding, mixed states is composed of various states with their corresponding probabilities, but what is the actual difference between maximally mixed states and maximally entangled states? ...
1
vote
1answer
34 views

What process happens in an IT nuclear decay?

I've been researching medical isotopes and alot of them decay by an IT path. Does anyone know what IT stands for? And what physical process is happening? Example: ...
1
vote
2answers
78 views

What is to be considered a “body” in physics?

Well, the question says it all; is there a definition of body in physics? What is to be considered a physical object and what it cannot?
1
vote
1answer
60 views

Statistical mechanics vs. many-body theory

Where is the basic difference of statistical mechanics with many-body physics? What are the systems which cannot be studied in statistical mechanics but in many body theory? After all we know ...
1
vote
1answer
58 views

What is the relationship between harmonic motion and the harmonics of a wave?

I learned about harmonic motion and harmonic oscillators a long time ago in physics, but I can't remember what the relationship between that and and the definition of harmonic in a wave. A harmonic ...
2
votes
1answer
24 views

What is the difference between a measurement and an experiment?

For example, say I want to determine the atomic structure of a bio molecule. I purify the molecule, get it to crystallize (probably though trial and error), shoot it with X-rays, observe the scatter ...