Questions tagged [terminology]

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

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Is quantum field theory a field theory of quantum mechanics or a quantum theory of fields?

Quantum field theory can describe and extend phenomena of classical fields, such as electromagnetism. I had assumed for a long time that it was itself a "field theory", by which I mean it is a set of ...
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1answer
204 views

What does 'Truth-level' mean in Particle Physics? [duplicate]

I am sorry to ask an obvious question but I have tried looking this up on Google and cannot get an answer. In particle physics, when it is said that something is 'truth-level', what does that mean? ...
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2answers
127 views

What to call an object which is in motion but not accelerating?

I began learning about acceleration and according to the source i learned from an object only accelerates when there is change in vel. &/ direction... what i am wondering is what do you call it ...
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0answers
56 views

Is gauge invariance the same as gauge symmetry?

I am studying Gauge theory using Wikipedia and need a little clarification on the difference between gauge symmetry and gauge invariance. For sure it has probably already been addressed on this site, ...
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2answers
62 views

Direction of temperature gradient while studying thermo electric effects

What is the direction of temperature gradient, when we study about thermoelectric power. And what is exactly meant by up and down the thermal gradient?
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1answer
95 views

Why is velocity gradient not called a velocity Jacobian?

I started thinking about the rate of deformation of fluid in the boundary layer. but here we consider only one of the components of the velocity vector (which is a scalar). But what about just general ...
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2answers
1k views

Why are hydrogen, helium and neon known as quantum gases in the mid-20th-century chemical literature?

So, while reading over equations of states, I learned that quantum gases do not conform to the same corresponding state behavior as normal fluids do. Why are these known as quantum gases and why do ...
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1answer
53 views

Feynman Probability lecture 6 - probability density graph

I'm trying to understand the 6-7 graph in the Feynman lecture 6 on Probability chapter (6–4) A probability distribution He says: "We plot $p(x)$ for three values of $N$ in Fig. 6–7. You will ...
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2answers
421 views

What is the difference between sound and vibration?

As far as I know, the only difference between sound and vibration is that sound propagates but vibration does not. In most cases, they are the same. Please help clarify these concepts.
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103 views

What is the exact difference between static pressure and temperature?

If temperature is the average amount of energy and static pressure is the amount of internal energy, wouldn't the static pressure be the same as the temperature?
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1answer
60 views

What is the correct name of this 'basis label operator'?

What is the correct name for this operator I am calling the 'basis label operator' which returns the constant function of the eigenvalue for all vectors in a (momentum) eigenspace? $$\hat{O} : \hat{O}...
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2answers
53 views

Why is optical contact called optical contact?

Why is optical contact called optical contact? whats the meaning of the 'optical', when the concept of optical contact bonding has nothing to do with optics.
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0answers
52 views

Is there a name for symmetry in which fermions and bosons are in identical adjoint representations?

In a Yang-Mills theory, with gauge group $G$, if the Fermions are in an adjoint representation then for every Fermion with "charge" $Q$ there is a boson with charge $Q$. i.e. there is no difference ...
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1answer
65 views

Continuum Physics

How distinct is fluid dynamics from continuum physics? I've heard it is a subset and by the definition of the subject's name, it seems likely to be the case. Can anyone please clarify?
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1answer
143 views

What does 'high-beta' mean for a fusion reactor?

I see the term 'high-beta' a lot, but cannot find a definition. When I type it into Google, I mostly see results about a Lockheed Martin fusion reactor project.....
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3answers
163 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
153 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
38 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
104 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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3answers
4k views

Difference between uniform and constant acceleration

I am confused about the difference between uniform and constant acceleration. When I look online, people say there is no difference, but I thought there is. Isn't uniform acceleration when speed is ...
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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
87 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
54 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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0answers
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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
671 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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0answers
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
73 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
1k 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
148 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
41 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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0answers
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
205 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
235 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
128 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
155 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
178 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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0answers
63 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
305 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
425 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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66 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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29 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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3answers
160 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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0answers
53 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
599 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
59 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
88 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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4answers
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
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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 ...