Questions tagged [terminology]

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

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166 views

In general, how are representations used in physics?

I want is a basic overview, if there is one, of the meaning (and purpose) of the word representation in general terms. I have looked up sources such as Particle Physics and Representation Theory, but ...
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1answer
170 views

What are spin-2 spherical harmonics and why are they needed?

A function $f(\theta,\phi)$ (with $\theta,\phi\in \mathbb{S}^2$) can be expanded in terms of spherical harmonics $Y_{l.m}(\theta,\phi)$. Recently, in this Particle Data Group review titled Cosmic ...
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2answers
40 views

Distinction between “assumption”, and “build in definitions” - What is considered an assumption in a physical model?

This question I want to deal with the basics of modelling a physical theory: Let's say we start with observing in the world (be it little bubbles in the water, a particle moving, a pattern in the ...
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1answer
112 views

How to understand the Planck data?

I want to analyze the Planck data to get relevant Cosmological parameters from it. But I don't know how can I go about this. Can anyone guide me? Online sites/Research papers would be nice. I know ...
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1answer
2k views

Difference between real and virtual objects (optics)

I do know the difference between real and virtual images, cf. e.g. this Phys.SE post. I would like to know the difference between the real and virtual objects. I need a real life example.
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1answer
88 views

What is “fundamental” in physics?

Sorry about the broad question. I'm still learning to frame the questions on Physics StackExchange. Currently researching the nature of interactions in philosophy. My question is: When physicists ...
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1answer
63 views

Is mass a property or a quantity?

From definition mass is the amount of matter that an object has. So why we call it a property? What is the difference between a property and a quantity in the dictionary of physics? Wiki says physical ...
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67 views

Mean field critical exponents and the Gaussian approximation?

A while a go I asked this question on the difference between mean field theory and the Gaussian approximation. This question is related to that. The mean field critical exponents for the Ising model ...
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5answers
754 views

Why is normal force sometimes called “reaction force”?

I know that normal force is not a reaction force to the gravitational force: first because the gravitational force is from Earth on the object (action force), thus the reaction force is simply from ...
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48 views

What is an Amperian man?

In Cagniard(1953), Basic theory of the magneto-telluric method of geophysical prospecting he writes, "If a current circulates in the ground along OX, OY is at the left of the Amperian man looking ...
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1answer
79 views

What are the differences and similarities between dynamical tunneling and quantum tunneling?

In case of a double well potential, particle can tunnel from one well to another and this process is known as quantum tunneling or tunneling in general. I want to know about dynamical tunneling and ...
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1answer
80 views

Why doesn't magnetomotive force have units of force?

Why does it have units of Ampere-turns and not Newtons? Is it a current, or turns mean metres?
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1answer
2k views

What are entropy and reversible processes really?

I'm confused about the concepts of entropy and reversible processes. Before explaining the definition of entropy, they used the term "reversible process" without defining it formally. Then, when ...
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1answer
155 views

Meaning of reverse banked

I have been given the following question of Newtonian mechanics. A road has a (horizontal) curve of radius R. The engineer was, however, unclear on the concept, and banked the road (angle Ɵ) in THE ...
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1answer
45 views

What is the difference between inclusive measurements and differential measurements?

While reading about the current status of the top quark analysis at LHC I come across these two terms: inclusive measurement and differential measurement? What do they mean? I came across another ...
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43 views

I'm looking for the name of the specific properties of physical quantities - if it already exists [closed]

My working names are extensivity or degree of nonaditivity of this quantity, but I wonder if there exist a generic term of its. Degree of nonaditivity of quantity $f$ is defined as a minimal $k$, ...
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1answer
209 views

Understanding a joke in Zwiebach - “A first course in string theory” [closed]

So fairly early on Zwiebach discusses the quantum mechanics of a one-dimensional square well. He then goes on to add an extra dimension which is compact to demonstrate how one can understand ...
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1answer
26 views

Questions regarding the elements of vector space spin representations act on

Elements of vector space spin-$1/2$ representations act on are spinors. What about half-integers in general? And what about integer spins? Do spin-$0$,$1$ reps always act on vectors?
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1answer
258 views

Chrisoffel Symbol and Spin Connection

Im currently studying general relativity from Sean Carroll's book Spacetime and Geometry: An Introduction to General Relativity. In this book, I found that, in a simple way, Christoffel symbol is a ...
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1answer
133 views

What is Cosmic Downsizing?

I've had a quick look at a few lecture pdfs and papers as supplementals to my own given lecture notes, but I can't seem to get a proper explanation for what cosmic downsizing is. The closest ...
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2answers
163 views

How can an affine geodesic exist on a curved manifold?

I'm reading Inverno's "Introducing Einstein's Relativity". I think I understand how the author derives the affine geodesic equation. He considers the tangent vector to any curve as the vector field. ...
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1answer
214 views

Semantic distinction between “Partition Function” and “Generating Functional” in QFT?

I am just now learning about these, and I have seen them defined as follows: The generating functional for a set of fields $\phi_i$ is defined by: $$Z[J_i]=\int\mathcal{D}\phi_i e^{i(S[\phi_i]+\int ...
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65 views

Mean Field Theory neglects what flucutations?

This is a topic that has being confusing me for a while. A general phrase that is used in the literature is that: Mean Field theories neglect fluctuations My questions is what is meant by ...
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1answer
309 views

Is there a word for a surface that DOES have friction? [closed]

When talking about models in physics, I want a way to differentiate between surfaces that have negligible and considerable friction. We have "frictionless" for surfaces where friction is negligible, ...
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1answer
474 views

What is the meaning of 'systemic velocity' of galaxies?

I came across the term systemic velocities of galaxies. Can you please explain what it means?
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76 views

Stress tensor decomposition and names for different components

The stress tensor can be decomposed into a spherical component (which is a scalar multiple of the identity tensor) and a deviatoric component which is the original tensor with the spherical component ...
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30 views

“Intensity” as a unified term

I am seriously having trouble with the word “intensity”. Does it have different meanings when it is placed next to another word (light intensity for example) or does it always mean the same (power/...
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164 views

Order Parameter and Mean Values?

I am confused about mean values and order parameters in specifically Ginzburg-Landau Theory. From what I have read$^1$ the order parameter is in general given by: $$\phi=\left<m\right>_\beta\tag{...
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54 views

Clarifying the physical significance of the attenuation coefficient

I have seen several sources define the attenuation coefficient as the fraction of a beam's intensity which is attenuated per unit distance e.g. "the fraction of attenuated incident photons in a ...
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2answers
674 views

What is the difference between orbital velocity and critical velocity? Are their values similar or not?

As critical velocity is the minimum velocity required to put a satellite into orbit. And orbital velocity is the velocity required to keep a satellite moving in an orbit.The value of critical velocity ...
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1answer
62 views

Why do we use $Q$ for heat?

Of course letters are of few interest if something at all. But when reading some notes the question just appeared: Why do we use $Q$ for heat? Googling it shows many links but none of them seems ...
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1answer
89 views

Kinds of ensemble

In statistical mechanics, why microcanonical, canonical and macrocanonical ensemble are called that way? Is there any reason according to the size of the system they can describe properly ( I don't ...
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3k views

What would qualify as a deceleration rather than an acceleration if speed is unchanged?

The instantaneous acceleration $\textbf{a}(t)$ of a particle is defined as the rate of change of its instantaneous velocity $\textbf{v}(t)$: $$\textbf{a}(t)=\frac{\mathrm{d}}{\mathrm{d}t}\textbf{v}(t)....
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1answer
75 views

Is there a name for the relativistic phenomenon where time is ahead/behind in the direction of travel?

One of the Lorentz equations is $$t ′ = \gamma \left( t − \frac{v x}{c^2} \right) $$ This shows that clocks that are synchronized in the inertial reference frame will be offset in the observer ...
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2answers
102 views

What is the need of term 'closed circuit'? [closed]

If a circuit is a closed path in which charges can flow then why do we have the term closed circuit? Doesn't the definition mean that a circuit is always closed.
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1answer
125 views

Spring constant, but intrinsic to material, not rest length

If you have two metal springs that are coiled in the same way, but one is twice the length of the other, the spring constant will be half as large for the longer one. That makes sense of course. What'...
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110 views

Are component of vectors vector and can we divide them into components?

We know that two vectors can sum up and make one vector. And dividing a vector into components is the opposite process of summing vectors. Then the components of vectors should also be vectors. Are ...
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1answer
692 views

What are Next-to-Leading-Order (NLO) corrections?

I'm currently studying Particle Physics and HEP and this acronym is omnipresent. I know it means next-to-leading-order but, what is exactly the physical meaning of LO and NLO?
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1answer
121 views

Confused about micro, macro, ensemble, accessible, possible ect. states

I'm hopelessly confused about accessability of microstates and macrostate. Let's imagine ideal gas box, A, with parameters: $T_\mathrm{A}$ (temperature) $P_\mathrm{A}$(pressure), $V_\mathrm{A}$(...
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385 views

Local and Non-Local Potentials

Can anybody explain the difference and concepts between local and non-local potentials in light of quantum mechanics?
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1answer
80 views

The term “Configuration” in quantum field theory, what does it mean?

I would like a thorough explanation of what the word “configuration”, means, as used in ‘Quantum Field Theory’. I have seen the word used in various phrases, such as “the field configuration φ(x)”, “...
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1answer
101 views

Equivalence between ghosts?

Ok. I'm trying to get the terminology right about the term ghost in physics. Is there any equivalence between these terms? Faddeev-Popov ghosts Paul-Villars ghosts Landau ghost The vanishing ...
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65 views

What is meant by “Almost orthogonal”?

Figuratively speaking, when two quantum objects’ states are ‘almost orthogonal’, are they in some physical sense ‘almost blind’ to one another?
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1answer
37 views

What is the difference between functionalisation and passivation?

I know the basic principle of functionalisation and passivation is to add Ligands to the surface of nano particles which can limit the growth of nano-crystals in fabrication and improve proprieties ...
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1answer
492 views

Finite size effect

What does finite size effect mean in physics? I googled it and that is what I got: "When studying any macroscopic system with a very large number of degrees of freedom, invariably make an ...
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1answer
71 views

Acoustic, optical, ferromagnetic and antiferromagnetic spin-waves?

In the context of spin-waves I have seen the following words as descriptors*: Acoustic Optical Ferromagnetic Antiferromagnetic which I have seen used together e.g. "acoustic ferromagnetic spin ...
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1answer
188 views

What do the symbols $⊕$ and $⊗$ mean?

Please have a look at this presentation on Young tableaux, I'm trying to understand the signs I mention there - what do the $\otimes$ and $\oplus$ symbols mean?
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73 views

Is Potentiometer a variable resistor or a measuring instrument?

I have used Potentiometers many times, and what I understood is that it is a variable resistor. However, my Physics teacher says that he is SURE a potentiometer is used to measure stuff, and is NOT a ...
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2answers
71 views

Formal Term for an invariant constant to all observers

I was thinking of the speed of light and realized I don't know how to quickly name the concept of "physical quantity that is measured to be the same in all reference frames". Are there examples of ...
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1answer
65 views

Is there a name for a function or field of position and rotation?

A scalar field is a function which has a different value at all positions e.g. $\phi(x)$ where $x$ is a 3-vector. Imagine that the value of a field depended not only on the position of a detector but ...