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

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34 views

Physical intuition on bivector in fluid dynamics

Reading the M. S. Howe's Theory of Vortex Sound I've ran into this exoression and equation: Let $v_A$ denote the fluid velocity at a point A at $x$. The velocity $v_B$ at a neighbouring point B at ...
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3answers
631 views

Should the term Watt's Law be used for $P = IV$?

I'm revising some electrical curriculum for a technical training program. In the curriculum students have to calculate values using Ohm's law and the equation $$\text{Power = Current * Voltage}$$ ...
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0answers
38 views

Names for various color indices in QCD

In Quantum Chromodynamics with $\mathrm{SU}(3)$ there are at least two types of color indices: Indices $a$, $b$, … that index the eight generators of the group $\mathrm{SU}(3)$. In some sense they ...
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2answers
653 views

What is polytropic index?

What is polytropic index? What is the connection between it and work of an adiabatic system? I tried surfing but didn't able to find a proper answer for that.
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1answer
54 views

Difference between escape velocity and speed [duplicate]

What is the difference between escape velocity and escape speed , is their any error if we use them interchangeably?
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5answers
2k views

What is a state in physics?

What is a state in physics? While reading physics, I have heard many a times a "___" system is in "____" state but the definition of a state was never provided (and googling brings me totally ...
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1answer
238 views

What is difference between polarization and polarizability and how do we define it? [closed]

The book of physics that I have, uses the word "polarization" sometimes and sometimes uses the term "polarizability" and I am getting confused. And I even checked the dictionary for the term ...
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4answers
105 views

Why the word “measurement” all the time?

I'm trying to learn more about the properties of light. In all the youtube videos and related to the two-slit experiment, the explanations always say that "measuring" can change the outcome. Why do ...
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1answer
39 views

What is the different between Poisson Nernst–Planck and Poisson Navier–Stokes in the Electrolyte?

I am now studying about electroosmosis flow phenomena which is governing by the Navier-Stokes equation and Poisson equation. By combine these two equation we can describe the electrolyte flow velocity ...
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0answers
40 views

Radiative corrections and stability

What is meant by the terms radiatively stable and radiatively unstable? I know that when calculating physical observables in quantum field theory, such as the mass of the electron, to obtain a more ...
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1answer
44 views

Is there a name for leptons that are not neutrinos?

Is there a name for leptons that are not neutrinos? Not sure if its exists, its not particularly easy to search for. Is there a name for the set of charged leptons (or leptons that are not neutrinos)? ...
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5answers
10k views

How do the terms comet, asteroid, meteoroid, meteor and meteorite differ?

These terms are frequently used interchangeably by the uninitiated to mean approximately “space rock”. In practical terms, how do their meanings differ?
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1answer
108 views

Does 'focal length' mean something different with lenses and pinhole cameras?

Sometimes different but related things have the same name by some tradition or accident, causing a lot of headache to newcomers to a field. I would like to come to clear terms with this: does the ...
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0answers
101 views

Mean Field Theory vs. Effective Field Theory

I am reading my many-body quantum physics textbook, and specifically the section on Mean field theory. It seems that the Mean field approximation in the Hamiltonian formalism must be equivalent to ...
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2answers
84 views

What exactly is an arbitrary parameter?

I was reading the article Turning Points: A meeting with Enrico Fermi by Freeman Dyson (available e.g. here), and I had a question about Dyson's use of the term 'arbitrary parameter'. More ...
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3answers
203 views

What does “the fabric of space and time” actually mean? [closed]

I've heard the term "the fabric of space and time" in both physics and science fiction, and although I know it has something to do with general relativity, I don't understand what, specifically, ...
3
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2answers
77 views

Heuristic explanation of the difference between vectors and scalars in physics

I'm trying to give a student a (physically) intuitive, heuristic explanation as to why certain quantities are vectors and others are scalars. Here is what I have come up with: Scalars are quantities ...
19
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2answers
45k views

What exactly is the difference between advection and convection?

After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms. Sometimes, the term convection seems to ...
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1answer
91 views

What is the difference between Fermi level and Fermi edge?

Just as in title: What is the difference between Fermi level and Fermi edge? My friend makes some research about XPS and he encountered this term. He knows what is Fermi level, but never heard about ...
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1answer
111 views

What is the different between a dark state and a ground state?

In a atomic quantum system, typically discussing in quantum optics, there is something called dark state. A dark state is a state of a quantum system that does not emit any photon. A ground state also ...
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1answer
196 views

Why do astronomers call all elements heavier than helium “metals”?

I understand that a scientific term need not be constrained by its etymology. But is there some significant reason why astronomers choose to call all elements heavier than helium "metals"? Are ...
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2answers
217 views

What is the clear cut difference between isotropic and anisotropic spin exchanges?

When are spin exchanges said to be isotropic or anisotropic? I have read several articles on this and can not differentiate these concepts properly.
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1answer
123 views

How is the formula for the capacitance of a parallel plate capacitor derived?

I have seen in I.E. Irodov that if the permittivity is given as $\epsilon$ then we can find the capacitance as $$C = \frac{\epsilon A}{d}$$ but I wonder whether it is dimensionally correct or not and ...
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2answers
378 views

What is meant by 'a perfect dipole'?

Question What is meant by a perfect (electric) dipole? Additional information I came across the term in this question Force from point charge on perfect dipole and also in a textbook (which does ...
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0answers
27 views

Escape speed or Escape Velocity? [duplicate]

Which one should be the correct term escape speed or escape velocity? In one book it is given Speed whereas in another its velocity.
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0answers
194 views

Exact (quantitative) definition of “knee” and/or “cut-in” voltage?

Sort of a 2-part question: 1) I know they are used interchangeably but are the "knee" and "cut-in" voltages of a diode actually the exact same thing? I had thought that the "cut-in" voltage was ...
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2answers
120 views

Confusion with Blackbody Radiation

A blackbody is a theoretical object that perfectly absorbs all the light that falls on it. From what I understand this is an ideal situation and does not actually exist in reality. Certain objects are ...
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0answers
39 views

What does 'vector-like' mean?

What are properties of vector-like field/particle? What's the counterpart of it? Chiral like?
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1answer
1k views

Is there a difference between Electric and Electrostatic Field?

Is there a difference between Electric and Electrostatic Field? All I know is that they both represented with same law suppose we have a Charge placed at the Origin: ...
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3answers
784 views

Why are diffraction gratings not called interference gratings? [closed]

It seems to me that diffraction gratings are completely described by the double slit experiment-why then is it called a diffraction grating?
2
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0answers
147 views

What is a Fermi arc?

What is meant with a Fermi arc in the context of Weyl semimetals? Is this the just a one-dimensional Fermi surface? For example, in electron-doped graphene, the Fermi surface consists of 2 disjoint ...
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2answers
53 views

Sound speed vs Speed of sound

Are 'sound speed' and 'speed of sound' the same thing? If not, what is the difference? If they are, could you clarify how the speed of sound applies in the below description of gaseous clouds? ...
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1answer
29 views

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore?

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore? I was going through the 'stacks' present in an thermoacoustic refrigerators there I came across the ...
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5answers
450 views

Is Parity really violated? (Even though neutrinos are massive)

The weak force couples only to left-chiral fields, which is expressed mathematically by a chiral projection operator $P_L = \frac{1-\gamma_5}{2}$ in the corresponding coupling terms in the Lagrangian. ...
3
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1answer
163 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 ...
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1answer
55 views

Is “applying a voltage” the same as “applying a potential” to an electrode?

From what I understand, voltage is the potential difference, but it seems like the terms are used interchangeably. This is confusing me because I am only just learning what these terms mean. I'm also ...
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4answers
15k views

What is the difference between a pulse and a wave?

I wanted to ask what is the difference between a pulse and a wave? According to the definitions of them, they are almost the same. In the websites I looked at, the difference between them was ...
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1answer
49 views

How Does Rotational and Turbulent Motion Contribute to the Pressures of Dynamical Systems?

Rotational and turbulent motion can deepen a gravity well in a galaxy or galaxy cluster. In an analysis of the mass components of a large body, this would appear to be one of the components. Does it ...
2
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0answers
340 views

What was Feynman's famous formula?

In Welton(1983), Memories of Feynman, Welton mentions two formulas which he denotes as Feynman's Famous Formula (FFF) and FFF #2. Which famous formulas is he talking about? Is he maybe talking about ...
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6answers
12k views

Difference between theoretical physics and mathematical physics?

I'm a huge fan of mathematical physics and I know what the formal definitions of those two areas are, I've seen them. But I still get completely baffled when someone asks me to explain it simply. The ...
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1answer
44 views

What does “n-particle reducible” mean?

I am reading Ramond and in page 112 he says "In $\lambda \phi^{4}$ theory, diagrams can be at most three-particle reducible". My question: whether the individual Feynman Diagrams are treated as ...
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4answers
2k views

What is pure energy?

Inside the core of a star thermonuclear fusion reaction fuses hydrogen atom into helium releasing massive heat/light and energy.When a black hole eats up enough stars and gases it devours itself by ...
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0answers
30 views

What is the pure form of energy? [duplicate]

What is the pure form of energy? Einstein in his energy mass equation derivation said that electromagnetic radiation is pure form of energy.
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3answers
133 views

GR: Pseudo Riemannian or Riemannian?

Is General Relativityy described by Pseudo-Riemannian manifold or Riemannian manifold? I cannot understand the vast difference between the two manifolds. In books, General Relativity is looked as a ...
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0answers
23 views

What does “at%” refer to in sol-gel method?

I'm reading on the preparation of ZnO thin films for UV stimulated emission and I found a method called Sol-Gel. During this I found a paragraph saying, " the ratio Ag/Zn in the sol is 3 at%......". ...
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0answers
12 views

What is the difference between a planet and a dwarf planet? [duplicate]

What is the difference between a planet and a dwarf planet? And is there a way to determine a dwarf planet from a normal planet in a unknown solar system? (If we discover a unknown solar system)
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2answers
621 views

What is the difference between a hollow (sphere/cylinder) and a shell (cylinder/sphere)? [closed]

First of all, it was hard to "tag" this question ! Anyways, I see some contradictions in what a shell or a hollow cylinder is in some sources in the internet based on some figures they show. I ...
3
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1answer
99 views

What is the difference between a quasar and an Active Galactic Nucleus (AGN)?

In answering another Phys.SE question about quasars - Why no new quasars? - an issue arose about which object is the nearest quasar. That got me puzzled. To what is the label "quasar" attached, as ...
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2answers
67 views

What is $\mathcal{L}_M$?

Usually we derive the Einstein field equation in vacuum starting from E-H action $$S= \int{\sqrt{-g}d^4x(\frac{c^4}{16\pi G})R}.$$ But in case we wanted to get ...
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4answers
64k views

What is the difference between phase difference and path difference?

I have learnt that path difference is the difference between the distance travelled by two waves meeting at a point. If that is path difference,then how will one know what is phase difference and how ...