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

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What is a geocentric altitude?

In NAO TN no.69, Yallop defines ARCV as geocentric difference in altitude between the centre of the Sun and the centre of the Moon for a given latitude and longitude, ignoring the effects of ...
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1answer
76 views

Difference between harmonic oscillator & coupled oscillators

Coupling, according to wiki, is the condition of two systems when they interact with each other. Now, I came across the terms harmonic oscillator and coupled oscillators. Now,what is the difference ...
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3answers
741 views

Definition of a year

Is there an acceptable definition of a year (in number of days)? Google Calculator: https://www.google.com/search?q=seconds+in+1+year returns 3.15569e7 seconds and then ...
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0answers
48 views

Why is special relativity so special? [duplicate]

The title says it really. Why is special relativity so special? I'm just curious as to how and why the term 'special' came to describe the theory of relativity where gravitational forces are ...
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3answers
95 views

What really is “inertial force”?

In Fluid Mechanics we often see the term inertial force when discussing Reynolds number. The problem is, I didn't really get what's this inertial force. Basically, the notion of inertia I have is that ...
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1answer
64 views

Is 'grapheme' a substance or a typo?

While reading Ref. 1 I came across the sentence Below we focus on the physics of ideal (single layer) grapheme. I did google search 'grapheme' but the results tended towards a completely ...
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1answer
44 views

The name of effect of liquid flow inducing flow to neighboring layers of liquid?

How do you call an effect, when liquid or gas stream is involving the neighboring layers of matter also move? Like on videos of rocket engines testing, when exhausting gas sucks an air and steam from ...
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2answers
188 views

Showing that Coulomb and Lorenz Gauges are indeed valid Gauge Transformations?

I'm working my way through Griffith's Introduction to Electrodynamics. In Ch. 10, gauge transformations are introduced. The author shows that, given any magnetic potential $\textbf{A}_0$ and electric ...
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1answer
74 views

Realistic Potential Wells

What is meant by the term "realistic" potential wells? I got stuck into the term as I don't know what are the limitations of the word realistic in this case. For example mentioned in line We ...
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5answers
543 views

Hilbert space vs. Projective Hilbert space

Hilbert space and rays: In a very general sense, we say that quantum states of a quantum mechanical system correspond to rays in the Hilbert space $\mathcal{H}$, such that for any $c∈ℂ$ the state ...
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2answers
127 views

Is it accurate to say “a wavefunction is a function of particle positions or momenta”?

Something has been bothering me for a while. I encounter this kind of statement everywhere: While a single particle is described by a wave function $\Psi({\vec r};t)$, a system of two particles, ...
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2answers
491 views

History of the names “Feynman-gauge” & “Landau-gauge”. How arised & how settled?

Warning: Students, stay away from antiquities. The aim to learn is to survive. Hi. Today the nomenclatures Feynman gauge and Landau gauge seem established, but could you explain the history? It's ...
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2answers
164 views

What is the difference between classical thermodynamics and statistical mechanics? [duplicate]

What is the difference between classical thermodynamics and statistical mechanics? To me, they are greatly different but are different approaches for explaining same thing. But I do prefer ...
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1answer
370 views

Does a ball resting on the ground have acceleration?

Does a ball resting on the Earth's ground have acceleration caused by gravity?
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0answers
82 views

If the field concept was invented by Faraday, then how did Newton interpret the $g$?

This is Newton's law of universal gravitation. $F=G\frac{m_1.m_2}{r^2}$ Gravitational field $g$ is derived from this formula $g=G\frac{m_1}{r^2}$ This is named gravitational "field" strength. If ...
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3answers
673 views

What does “nearly infinite mass” mean?

I am sure this is a silly question, but I was reading something that described the pre big-bang universe as having "nearly infinite mass." How can something be "nearly" infinite? The term seems to ...
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4answers
90 views

Is trajectory the same as an orbit?

Is trajectory the same as an orbit? I wanted to know about gravity assists, but most books I find are talking about different types of orbits and such. Are they related?
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3answers
83 views

Is wave superposition always equivalent to wave interference?

I'm confused when using these 2 words "wave superposition" and "wave interference" since their definition is very similar. So, are these 2 term the same?
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4answers
3k views

Catapult vs. Trebuchet

I have been looking at trebuchet designs lately, and I have noticed that most, if not all, have a sling attached to them. Without such a sling, the machine would be a catapult. In terms of the speed ...
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4answers
5k views

What is the difference between air pressure and atmospheric pressure?

I know that air pressure and temperature are inversely proportional. Now I saw in a book that "Atmospheric pressure decreases as we go higher and higher." But at greater heights the temperature ...
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6answers
5k 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
72 views

What are “two-centre integrals”?

Reading through some condensed matter physics literature I came across the term "two-centre integrals". Could someone explain what is meant by this in general? CONTEXT: "the overlap matrix and the ...
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0answers
22 views

Relativistic non-linear Walecka model

What is meant by a relativistic non-linear Walecka model? What are some various sources to study it? [And why cannot Google show a satisfactory result to such a simple question?]
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3answers
524 views

What's the difference between “numerical methods” & “mathematical analysis” as said by Feynman in his lectures?

While reading his lectures, I came to these lines: On the basis of Newton's second law of motion,which gives the relation between the acceleration of any body & the force acting on it,any ...
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1answer
160 views

Where did the Word 'Physics' Come From? [closed]

As the title suggests, where did the name for the discipline 'Physics' come from? - does it mean something in Greek?
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0answers
49 views

What does “downshear” mean?

I occasionally read descriptions such as "downshear of the vortex" in meteorological publications. What does this mean?
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7answers
37k views

What does the magnitude of the acceleration mean?

I am a little confused as to what the magnitude of acceleration is and what it means.
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1answer
35 views

Difference between astronomy and astrophysics [duplicate]

In my university, the department for astronomy and astrophysics are distinct. I want to know what's basically the difference between the two fields?
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0answers
41 views

Confusion about the use of the term “Phase Space” in Strogatz text

I've just started learning about Hamiltonian mechanics, and from the definition given in Taylor's classical mechanics, phase space must always have an even dimension. However, I recall from reading ...
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1answer
7k views

What is the $C_p/C_v$ ratio?

Recently in our chemistry class we read that the $C_p/C_v$ ratio of the inert gases is 1.66 thus they show inert nature. I asked my teacher what was $C_p/C_v$ ratio but he didn't answer me. So I want ...
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4answers
918 views

What is the Difference between a Lepton and a Fermion?

As the Title Says: I am Wondering what the Difference between a Lepton and A Fermion is. I know they both have an ½ integer spin number e.g. a electron, an atom with an odd mass number such as ...
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3answers
62 views

Image angle illusion [closed]

I am not sure whether this question on-topic here. (please suggest to migrate if this is off-topic) What is the phenomenon/illusion (or something else?) known as where in a photo of a person, the ...
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1answer
134 views

What is this simple mechanism called? [closed]

I often build with Lego and use this mechanism: It converts the rotational movement to linear by making the stick between the two blocks go back and forth. What is this mechanism called?
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1answer
62 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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6answers
833 views

Gibbs free energy intuition

What is Gibbs free energy? As my book explains: Gibbs energy is the energy of a system available for work. So, what does it want to tell? Why is it free? Energy means ability to do work. What is ...
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3answers
77 views

What is “a vector of $SO(n)$”?

I'm watching (or trying to watch) this lecture from NPTEL on classical field theory. I've understood everything in the series up till this point, including the first half of the lecture on elementary ...
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1answer
129 views

Does “normal torque” exist?

Is there any force called normal torque? If a ruler is spinning, and it hits the floor, obviously it will stop. The floor must be exerting a "normal torque" on the ruler. If this exists, please tell ...
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1answer
62 views

The spin and weight of a primary field in CFT

A primary field in Conformal Field Theory transforms as $$\phi (z,\bar{z}) =\left(\frac{dz}{dz'} \right)^h \left(\frac{d\bar{z}}{d\bar{z}'} \right)^\bar{h}\phi (z',\bar{z}') $$ under a conformal ...
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4answers
1k views

“Slightly off-shell”?

I'm not new to QFT, yet there are some matters which are quite puzzling to me. I often come across the statement that real particles (the ones we actually measure in experiments, not virtual ones) are ...
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1answer
101 views

Is charge transfer from A to B positive or negative?

I see this term pop up a lot -- for instance "charge is transferred from atom A to atom B", but it's never specified whether they're talking about positive or negative charge. I know electrical ...
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2answers
1k views

Differences between astronomy, astrophysics and cosmology? [closed]

What is the main difference between Astronomy, Astrophysics, and Cosmology? I have the impression that astronomy is a subject that runs parallel to physics but it is outside the physics field. This ...
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1answer
86 views

Is there a scientific term for star formation?

It might be my stupidity to think that many laymen terms that most people use to describe some physics phenomena usually have a scientifically accepted term or name? The process of star formation, ...
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4answers
548 views

What is an interpretation of quantum mechanics?

In the sense of "Copenhagen Interpretation", what exactly is an interpretation? What purpose does an interpretation serve? Can an interpretation be tested or even be correct or incorrect independent ...
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2answers
464 views

What is a gauge in a gauge theory?

As I study Jackson, I am getting really confused with some of its key definitions. Here is what I am getting confused at. When we substituted the electric field and magnetic field in terms of the ...
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1answer
36 views

What is “Lifetime Intensity” in photoluminescence?

I'm reading an article "Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots". Link The reasearchers are writing about increase in "lifetime intensity" and even ...
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2answers
153 views

Is uniform circular motion an SHM?

I know the projection along a diameter is an SHM but is circular motion itself an SHM? If we consider the mean position to be the center of the circle then the centripetal acceleration is proportional ...
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1answer
114 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
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1answer
159 views

Why is a dipole moment called a dipole moment?

The General Formula for a moment is the following one: $$ \vec{M} = \vec{r} \times \vec{F}. $$ However the formula for a dipole moment is this one: $$ \vec{p} = Q \vec{d}. $$ How comes this is still ...
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1answer
57 views

De Donder Weyl theory

Im trying to get my head around what the difference is between a symplectic and multisymplectic manifold is. My understanding currently is that on a symplectic manifold time is the parameter that ...
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1answer
252 views

Definition of mean free time in the Drude model

In the Drude model they derive a formule for the conductivity of a conductor. I wonder though how the main free time $\tau$ is defined in this formula. Wikipedia says that it is "the average time ...