Questions tagged [terminology]

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

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98 views

Is every chemical reaction a nuclear reaction?

This is a PhD-level question that I'm sorry to say is likely to annoy many a high school teacher or university professor trying to get their students to understand the difference between chemical and ...
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Why are “magnetic field lines” called “lines of force” when they are perpendicular to the direction of force? [duplicate]

Why are "magnetic field lines" called "lines of force" when they are actually perpendicular to direction of force (Lorentz force,cross product)? It makes sense to call "field lines" as "lines of ...
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135 views

Particle physics jargons - generations, family and flavor

The question is pretty much in the title. What is the difference between the words generations, family and flavour?
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“Subatomic physics” terminology

Unlike the previous question which was closed very early which presents the context of this question, I am asking about the terminology of "subatomic physics" and NOT about a specific book. I would ...
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Why is Cauchy horizon named after Cauchy?

I think the title says it all; I have done a lot of Googling, but I could not find the answer. Since (I assume) the concept was discovered after Cauchy's death, I speculate that there is a connection ...
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256 views

What is the name of the variable $b$ in the equation $F=-bv$?

I saw that the equation F=-bv is used for the drag force for damped harmonic motion, where F is the drag force, v is the velocity of the hanging mass. Question) What is the name for b though? I saw ...
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What is the name of the paradox about (false) net electrical force in a system of two collinearly moving opposite charges?

Kirk McDonald said in his paper "Maxwell’s Objection to Lorenz’ Retarded Potentials" ( http://www.physics.princeton.edu/~mcdonald/examples/maxwell.pdf ) that (about Lorenz's concept of retarded ...
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Mathematical convention when using spatial indices: numerical $(1,2,3)$ versus Cartesian $(x,y,z)$ [closed]

When writing a document I find that I am switching back and forth between indicial notation for spatial coordinates. I would like to get your thoughts on the following examples accompanied with ...
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How Traction differs from Road friction?

I am an aspiring mechanical engineer & me n my team are going to manufacture a buggy for which i am going to design & manufacture the braking system. I have a problem in understanding The ...
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A question about superposition (possibly due to the English expressions)

I am currently reading the book ''The Outer Limits of Reason'' and encountered a description about which I am very confused. I am afraid to say, this may be due to the fact that I am not a native ...
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Exponential cosine-screened Coulomb potential

I know from various sources that the expression for the exponential cosine-screened Coulomb potential (ECSCP) with screening parameter $~µ~$ is $$V(~\vec r~)=\dfrac 1r~e^{-\mu r}~\cos(\mu r)\qquad\...
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What’s the difference between contact discontinuity and shock discontinuity?

Is there an intuitive, mathematical way to understand the difference between contact and shock discontinuities? From the standpoint of hyperbolic PDEs, shocks occur when the characteristic curves of ...
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Non-commutative field theory vs Non-commutative geometry

In the literature I have read about non-commutative field theory where the spacetime coordinates obey $$[x_i, x_j] = \theta_{ij}, \quad \theta_{ij} \neq 0.$$ However, I have also non-commutative ...
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Why is the name of the “Field line” is “Field line”?

Faraday-inspired "Field lines" are not always straight. 【My question】 Why is the name of the "Field line" is "Field line", not "Field curve"? This may be a question of the English language, but ....
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Is there a name of the reactionary force to the pressure drag due to flow separation?

To help me clarify my title's question, let me quote the text from Fundamentals of Aerodynamics, 5th Ed., by Anderson: P872, “the aerodynamic drag on a vehicle is the sum of drag due to the ...
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What is the vector representation of $\mathrm{SO}(6)$?

What is meant by the vector representation of $\mathrm{SO}(6)$? I have only encountered the term vector representation in the context of the Lorentz group $\mathrm{SO}(1,3)$, where it refers to the $...
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The origin and current usage of the phrase “transition probability” in Wigner's sense

The definition of transition probability by Wigner is the following The square of the modulus of the unitary scalar product $(\psi,\varphi)$ of two normalized wave functions $\psi$ and $\...
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How is Large Gauge Transformation a kind of global symmetry if it varies from point to point?

In "Lectures on the Infrared Structure of Gravity and Gauge Theories", Strominger considers the so-called asymptotic symmetries. If I got it right, the basic idea is that one chooses a set of falloff ...
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What exactly do we mean by 'Free spectral range'?

While reading about Fabry perot interferometers, we conclude that transmission can only happen when twice optical length of the cavity is equal to an integer multiple of the wavelength of the incident ...
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Looking for name of theory that expresses relations as transforms instead of functions

Please direct me to the appropriate area if this is not it. A few months ago I came across a theory published by a younger woman and an older man, both somewhat well known in relativistic and quantum ...
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“Bulk” in the context of Black Holes and Quantum Mechanics

In this video [1], what Preskill means by "Bulk physics?" I mean, what suppose to mean a "Bulk" in black hole physics context? $$ * * * $$ [1] (7:14 min) https://www.youtube.com/watch?v=PblxOXJt9pY&...
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Operators and physical quantities

Why, in quantum mechanics, do some authors say "physical quantities are operators" rather than "physical quantities are measured by operators"?
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What does the phrase “$s$-wave resonance” mean?

I saw the phrase "$s$-wave resonance" in various research articles: "Comparison of average s-wave resonance spacings from proton and neutron resonances" by Vonach H, Uhl M, Strohmaier B, Smith BW, ...
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Range of the interactions: long/short-range

I have seen in Long/short-range interaction that in scattering theory $𝑟^{−𝑛}$ is a short range potential for $n>1$ and a long range potential for $n\leq1$. Now, why do we say that van-der-Waals ...
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Is Lorentz-Invariant opposite to Lorentz-covariant? [duplicate]

I am having trouble understanding the meaning of these terms. Is it possible to be both Lorentz-Invariant and Lorentz-Covariant at the same time?
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If I am decelarating forwards am I accelerating backwards?

If I am in a car and I put the brakes on so that I am slowing down (decelerating) am I then accelerating backwards? e.g. If I am decelerating in this car at -5ms⁻² am I accelerating backwards at 5ms⁻² ...
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Are there any resonant frequency spectra that do not possess any harmonics?

I’m hoping that somebody can help clarify the following passage regarding standing waves and the systems that support them: Many systems that support standing waves have resonant frequency spectra ...
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What is a good definition for what this article talking about when it refers to “Universal Physics”?

I was puzzled when I read "Precise measurements find a crack in universal physics by Ingrid Fadelli" (Phys.org, Jan. 15, 2020). The article has some vague statements in the opening paragraphs about "...
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What is a distributed force?

I was reading a book called "Properties of Matter" by D.S. Mathur. And In the chapter titled "Elasticity", The book said that "Stress" is measured per unit area due to it being a distributed force. ...
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Clarification in the difference between metastable states and excited states

The answer of this question What is the difference between metastable states and excited states? is that the difference lie in the the time that the systems lie in a given state. So for example take ...
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What is the difference between metastable states and excited states?

In the book Mathematical concepts of quantum mechanics ,Stephen J. Gustafson Israel,Michael Sigal, they say The notion of a resonance is a key notion in quantum physics. It refers to a metastable ...
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What is the difference between “Inverse source problem” and “inverse scattering problem”?

As above in the title. I know the inverse scattering problem problem in the context of recovering dielectric profile of imaging domain from scattered fields measured at certain locations. But, what is ...
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What are $S$ and $L$?

In a helium atom, the total spin of the electrons is 0, suggesting that the total spin quantum number S is the sum of the ms quantum numbers (1/2-1/2=0). However, many sources say that the total spin ...
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What is baking and what are the effects?

In their experiment, Davisson and Germer had to bake the nickel mass because it was oxidized. What is baking and what does it do to the lattice of the metal?
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What's the difference between decay width and canonical decay width?

As I mentioned, I see this conception of "canonical decay width" in a paper, I looked up in the Wiki, but I can't find any thing could interpret this or any thing special about this, so I'm wondering ...
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How is $\delta \theta$ related to angular resolution?

Does the expression $\delta \theta \sim 3 ^\circ $ have a special meaning other than about 3 degrees? I was searching for the angular resolution of neutrino detectors and looking at the Super-...
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Is the ‘diffracting angle’ talking about the first minimum or first maximum?

So when we talk about diffraction for single slits, we refer to the first minimum as the ‘diffracting angle’. However, in other experiments with wave particle duality (for example electron ...
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What is gravitational radiation?

What is gravitational radiation (in association with gravitational waves)? Is it a form of energy/mass? Or is it just another word for gravitational waves?
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What are $a$ and $a^*$ called in the context of a classical harmonic oscillator?

Consider a harmonic oscillator defined by the coupled differential equations \begin{align} \begin{split} \dot{X} &= \omega Y \\ \dot{Y} &= - \omega X \, . \end{split} \tag{1} \end{align} ...
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Spacelike separation, special case

This is merely a terminology question. Consider two events A and B. Now suppose A and B happen in two different black holes, i.e. there is no way from A to B (or B to A). Is this fundamentally ...
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Precise definition of the vertex factor

Just a short question about the vertex factor in QFT. When I have an interaction Lagrangian $$\mathcal{L}_{\mathrm{int}}=-\frac{\lambda}{3!}\phi^3$$ with a real scalar field $\phi$, is the vertex ...
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Physical meaning of the space-space components $T^{ij}$ of the stress-energy tensor $T^{\mu\nu}$

The time-time component $T^{00}$ and the time-space components $T^{0i}$ of the energy-momentum tensor $T^{\mu\nu}$ are respectively called the Hamiltonian (energy) density and the momentum density. ...
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Going from wavepacket to wavefunction

Suppose we have a one-dimensional wave packet $$\varphi(p)=A\Theta[(\hbar/d)-|p-p_0|]. $$ I want to, at first, determine the constant of normalization, and the wavefunction $\psi(x)$. However, there ...
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Is it, in general, better to speak of potential energy density or of energy density? [closed]

I read in this article: Antimatter And here we are: at the very end of the feasibility spectrum into the fantastic. Antimatter is made of antiparticles, which have the same mass as particles ...
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What is motion?

I never thought of this before but when an $8^{th}$ standard student asked me to explain what momentum is, I simply said that it the amount of motion contained in a body and tried to explain that how ...
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What x20 x40 x100 magnification means?

I want to buy a biologic microscope for fiber analysis, thus I need to see details of a fiber of around 20μm. Could you please explain what "x20" magnification means? I understand that it will not ...
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What is a cold black hole in astrophysics?

I found the word 'Cold Black hole' in some academic papers. I think it is concerned with thermodynamics of black hole but I don't know exactly what is cold black hole. Please help me to understand ...
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Lifetime definition

In Walter Thirring book Quantum mechanics of Atoms and Molecules he says that the probability that a initial state $\Psi$ be again measured at later time is $|\langle \Psi|\exp(-iHt)\Psi\rangle|^2$ ...
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Decomposition of a Cartesian tensor

In "Modern Quantum Mechanics" by Sakurai J.J. he gives an example of a Cartesian tensor of rank $2$ which is a dyadic formed out of two vectors $\mathbf{U}$ and $\mathbf{V}$, i.e. $T_{ij} \equiv U_i ...
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Why is $m_{\ell}$ called the magnetic quantum number? What is its association with magnets?

I am going over my quantum lecture notes and I can't seem to link the quantum number $m_{\ell}$ with any magnetic property. It just seems to specify the shape of an orbital with a particular principal ...

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