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Questions tagged [terminology]

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

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42 views

about the muscle's tension's variables

I'm reading the paper "The Problem of the Interrelation of Coordination and Localization", which is written by N. Bernstein. The paper says, The degree of tension of a muscle is a function, in the ...
69 views

Mathematical term for the on/off gradient functions in MRI imaging

The slice selection gradients, as well as the phase and frequency, in MRI imaging are traditionally represented by on/off box or rectangular symbols: or My question is what is the mathematical name ...
399 views

Truncated $N$-Point Functions

In Quantum Field Theory, truncated N-Point functions (or truncated Green's functions) are the N-Point functions of diagrams with their external legs chopped off. I was told that the truncated N-Point ...
101 views

What does “as small as a fraction of an angstrom” mean?

I was reading my school textbook in which the following statement was given: The resolution of such an electron microscope is limited finally by the fact that electrons can also behave as waves! (...
77 views

What is kinetic theory?

What is kinetic theory? I am taking a course on fluid dynamics right now, and I have been wondering about one thing for some time now. We have three ways to look at a gas ($N$ particles): 1) ...
548 views

Meaning of the word 'canonical' in physics

I often encounter the term canonical in my study of physics. What does it mean? There is canonical momentum, canonical transformations and I have even heard the phrase 'proving something more ...
49 views

Is there a name for this phenomenon?

Imagine I have a cylindrical pipe closed on both ends with lids. I fill it with sand and compress the sand tightly. Now I hold the cylinder vertically and remove the bottom lid. The sand will counter ...
75 views

Four-vectors in relativity

I have a question about specifically whether the components of a 4-vector could depend on the position $x \in \mathcal{R}^4$, where I denote Minkowski space with $\mathcal{R}^4$. I know that the ...
44 views

Quantum state space constructing operator

If I use British money the amounts I can have are isomorphic to $\mathbb{Z}_{\geq0}$ (in pennies). If I also use Australian money, if I want to think about the amount I have in total, I can use ...
54 views

Quasi Static Reversibility Theorem

As far as I know, the definition of a reversible process is simply "a process that can be reversed". Meaning, that for an isolated global system containing the subsystem in question, its thermodynamic ...
56 views

Why is equipartition law called a theorem too, in some books? [closed]

In some books, the equipartition law is called a theorem. But a law is an observation, and cannot be proved. On the other hand, a theorem is something established using earlier assertions. So what ...
155 views

What does it mean for event generation and event reconstruction in Experimental Particle physics? [closed]

I want to do data analysis and there are some processes called event generation and event reconstruction. I want to know these terms that what does it mean in particle collider? Please guide me.
97 views

Large Lorentz Boost

I understand the general concept of a lorentz transformation and a lorentz boost. What does it mean for a lorentz boost to be large however? My current guess is that this is referring to a large ...
232 views

Is $\delta(r-ct)/4\pi r$, the 3D wave equation elementary solution, a transverse or longitudinal wave?

Background: https://en.wikipedia.org/wiki/Longitudinal_wave 'Longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the ...
127 views

What is the 'state space' of a quantum field theory called?

This is just a terminological question, not a question about reality or mathematics. I often want to talk about state spaces in quantum field theory. For example the space of [all possible vector ...
89 views

“Now-plane” of a particle

I am currently reading the book "Classical charge particle" by Fritz Rohrlich, and I struggle a lot with the appendix "space-like planes and Gauss's integral theorem". He says "the world line of a ...
177 views

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 ...
257 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? ...
128 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 ...
58 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, ...
86 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?
110 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 ...
2k 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 ...
58 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 ...
604 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.
132 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?
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}...
56 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.
53 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 ...
68 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?
155 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.....
175 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 ...
180 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 ...
42 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 ...
115 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 ...
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.
90 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 ...
73 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 ...
71 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 ...
906 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 ...
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 ...
82 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 ...
85 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?
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 ...
191 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 ...
48 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 ...
44 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 $k$, ...
214 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 ...
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?