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

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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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1answer
59 views

Why “colours” of light are given in wavelength not frequency?

If I understand correctly, when a beam of (monochromatic) light passes through media of different refractive indices, its wavelength changes but frequency remains constant. Why, then, are colours of ...
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1answer
12 views

Difference between hydrostatic and uniaxial pressure

I'm confused with these two terminologies. Does 'hydrostatic' means every direction while 'uniaxial' means one direction? What're they usually used for?
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2answers
18 views

Usage of singular or plural SI base units when written in both symbol as well as name [on hold]

I have multiple doubts related to the usage of singular or plural SI base units when written in both symbol as well as name. I have framed this question under two parts, namely, Part (a) and Part ...
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1answer
57 views

What is this equation $f^e = f^a - \nabla U$?

Recently in a mechanics class my prof scribbled down something looked like $$f^e = f^a - \nabla U.$$ Where he claimed $f^e$ is the external force on an object, $f^a$ is the applied force on the ...
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30 views

What are momentum, configuration and coordinate spaces? [on hold]

What is a momentum space, a coordinate space and a configuration space? Are they in classical or quantum mechanics or both? What are their similarities and differences and when, where and how are they ...
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1answer
36 views

What is meant by a “stiff” or “soft” equation of state (wrt neutron stars)?

I am currently trying to understand the history of the development of the equations of state and structure of neutron stars. In my textbook, I frequently encounter phrases such as "The ...
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2answers
67 views

Why isn't the Time-Independent Schrödinger Equation an equation of motion?

I thought an equation of motion was something where you are given a Lagrangian and, using the Euler-Lagrange equation, you then find the equations of motion for that system. Same basic idea for the ...
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3answers
43 views

Definition of non-degenerate metric tensor

We know that a metric has a property which is called non-degeneracy. I was searching for what does that mean and saw it associated with the fact that $det(g_{\mu\nu})\neq0$. How does this relate to ...
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1answer
63 views

What is the meaning of phenomenology?

From what I understand, phenomenology as it is used in science means talking about the details of a phenomenon without going deep into the fundamental physical processes that lead to the phenomenon. ...
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213 views

Fiducial volume in collider/detector physics

I'm trying to make some sense of ATLAS measurements for a personal project to learn how to use Pythia, and part of my work requires me to recreate the distribution for Z boson decay. I encountered the ...
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2answers
221 views

Quantum hadrodynamics

What is quantum hadrodynamics? Can anybody give a proper explanation? What are the standard books and sources of information that can be found on the internet for better understanding?
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1answer
32 views

What process happens in an IT nuclear decay?

I've been researching medical isotopes and alot of them decay by an IT path. Does anyone know what IT stands for? And what physical process is happening? Example: ...
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3answers
50 views

What is the difference between maximally entangled and maximally mixed states?

To my understanding, mixed states is composed of various states with their corresponding probabilities, but what is the actual difference between maximally mixed states and maximally entangled states? ...
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1answer
30 views

Kinematics and dynamics - what pattern do they portray?

The Equations which are derived for kinematics and dynamics are some patterns related to the body in motion. What is the demarcation in the pattern that kinematic equations and dynamic equations ...
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1answer
39 views

What is the relationship between harmonic motion and the harmonics of a wave?

I learned about harmonic motion and harmonic oscillators a long time ago in physics, but I can't remember what the relationship between that and and the definition of harmonic in a wave. A harmonic ...
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1answer
19 views

What is the difference between a measurement and an experiment?

For example, say I want to determine the atomic structure of a bio molecule. I purify the molecule, get it to crystallize (probably though trial and error), shoot it with X-rays, observe the scatter ...
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2answers
46 views

Do the matrices $S^{\mu\nu} = \frac{1}{4}[\gamma^\mu, \gamma^\nu]$ have a name?

Do the matrices $S^{\mu\nu}$ defined by $$ S^{\mu\nu} = \frac{1}{4}[\gamma^\mu, \gamma^\nu] $$ have a name ($\gamma^\mu$ are the gamma matrices)? They feel very important to me since they form a ...
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1answer
58 views

What is a “fundamental thermodynamic relation”?

My professor handed me a quiz in which he said something like (I don't remember exactly) "write down the four fundamental thermodynamic relations for $A,G,H,U$". I showed the differential elements of ...
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1answer
37 views

What's the difference between binding energy and separation energy?

My understanding of the two was as follows: the binding energy of a nucleus is, classically speaking, the energy needed to put together/take apart that nucleus completely (i.e. a measure of the strong ...
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2answers
63 views

Name for Earth?

What is the proper word for 'Earth', as in 'Solar' and 'Lunar'? I cannot find this anywhere; I am guessing there is a word that starts with geo?
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3answers
82 views

What is meant by phase, phase difference, in (and out of) phase in wave terminology?

What is meant by phase, phase difference, in (and out of) phase in wave terminology? How do you get the relation $$y=A\sin(\omega t + \phi)?$$ Since the graph of sin function is identical to that of a ...
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4answers
62 views

A reference frame is any coordinate system or just a set of cartesian axes?

In Physics the idea of a reference frame is one important idea. In many texts I've seem, a reference frame is not defined explicitly, but rather there seems to be one implicit definition that a ...
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2answers
77 views

What is the difference between leptons and baryons?

I am learning about the formation of the first atoms and, from what I am reading, before heavy particles, like neutrons and protons could form, there were already other types of particles, called ...
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1answer
40 views

What is a self adjusting force?

What is a self adjusting force? I searched it everywhere on internet but not got my answer and I have no other source to get its answer except this site so please help me.
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338 views

Given the Wikipedia notion of “arc length”, how is its manifestly real “signed variant” to be called and denoted?

I am dissatisfied with the presentation (not to say "definition") of "arc length", in its "Generalization to (pseudo-)Riemannian manifolds", as given in Wikipedia. (Who isn't?. But I'll sketch it here ...
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5answers
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Why are electromagnetic waves called waves even though they don't travel through a medium?

If waves are defined as the oscillation of a medium, why are electromagnetic waves called waves as they do not need a medium to travel through?
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1answer
28 views

Mutually Commutative

What is the definition of a Mutually Commutative set of operators? I've found articles describing a complete set of mutually commutative operators, but I can't actually find what mutually commutative ...
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33 views

Motion Integrals of a Particle in a Force Field

I am trying to wrap my head around the following problem: A point particle is moving in a field, where its potential energy is U=-α/r. Find first motion integrals. In our university we have no ...
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1answer
64 views

Why oobleck does not obey Newtonian dynamics? [duplicate]

In the following post we can see that some guys are walking on Non-Newtonian fluids. As far as I know that, we can not predict the exact amount of strain if we predict some forces. therefore the curve ...
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2answers
38 views

Is a constant transformation still considered a gauge transformation?

I've never even considered the possibility that a constant transformation would not qualify as a gauge transformation. But I'm reading a paper that seems to make exactly this distinction. In ...
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5answers
41 views

Who is said to do Work, me or the body?

If I subject my force to a body and it is displaced then the work is said to be done. What is that work done by? Is it said to be done by me or that body?
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1answer
40 views

What is the difference between the diffusion equation and the heat equation?

I know that the diffusion equation is a more general version of the heat equation. But what is the exact difference informally?
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1answer
25 views

What does it mean the term “probe brane”?

What does it exactly mean the term "probe brane"? People say for example: We put a stack of N branes at some point and then a probe brane ..." How do they appear in AdS/CFT? Can you give me an ...
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56 views

How can we count 17 particles in the standard model

This may be a bit of numerology, but I'd like to be able to make a statement like "There are 17 particles in the standard model" with some logical definition of a particle. But this statement is ...
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35 views

How would you define a difference in potential?

I'm currently in 12th grade, and am required to write an essay about physics and biology. The topic of the essay is the artificial brain (with the researches of the Human Brain Project in Switzerland ...
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3answers
95 views

What is basically the difference between static pressure and dynamic pressure?

What is basically the difference between static pressure and dynamic pressure? While studying Bernoulli's theorem, I came before these terms. The law says: When the fluid flows through a small ...
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1answer
42 views

What are the differences between special and general relativity? [duplicate]

What are the differences between special relativity and general relativity? I am looking for a naive, non-mathematical explanation.
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17 views

Definition of a semiconductor

Originally I had learned that solids are split into two categories: isolators/semiconductors, and metals. The fundamental difference between the two is the existence of a bandgap. Metals don't have ...
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1answer
27 views

Forgotten word meaning susceptability to direction

A little over a year ago, I encountered a descriptive word with respect to experimental physics, describing the phenomenon in which calibrating an instrument from one direction will yield a different ...
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1answer
20 views

In astronomy, what is a 'reflex orbit'?

In astronomy, what is a reflex orbit? The term is used in one of my books, but u don't find a definition for it. Googling it gives me articles about 'Oculocardiac reflex' which is not what I want. ...
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1answer
60 views

Does reverse biasing hold any meaning in case if both terminals are n type semiconductors?

When we talk about an n-p-n transistor in common emitter configuration, we often say that emitter-collector circuit (the one towards right) is reverse biased. In what sense it is reverse biased? Here, ...
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1answer
72 views

What is the difference between a parameter, a variable, and an operator in QM?

On the question why time isn't an operator, people will usually say that time is a parameter in QM (Time as a Hermitian operator in QM?) and not a variable. Can someone please distinguish between a ...
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1answer
28 views

Definition of a symbol $s_{NN}$ appearing in particle physics

What is the meaning of $s_{NN}$ in particle physics? See e.g. here http://www4.rcf.bnl.gov/brahms/WWW/thesis/karabowicz_phd_thesis.pdf page 18 in the pdf. What is its relation to energy? I ...
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1answer
54 views

Statistical mechanics vs. many-body theory

Where is the basic difference of statistical mechanics with many-body physics? What are the systems which cannot be studied in statistical mechanics but in many body theory? After all we know ...
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3answers
119 views

Is my conceptual understanding pertaining to heat & temperature correct?

From what I've understood: Heat is the total sum of kinetic energy translational energy possessed by individual atoms in an object. Temperature is the average kinetic energy translational energy ...
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1answer
56 views

What is a full cycle in damped oscillation?

Maybe it seems a dumb question, but I can't understand what the cycle in a damped oscillation is? Let's take an example: In harmonic motion, one cycle is the smallest distinguishable part of wave ...
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1answer
38 views

What does multi-periodicity mean in stellar pulsations?

How can there exist multi-periodicity in stellar pulsations? http://www.kitp.ucsb.edu/sites/default/files/kitp/preprints/moskalik2.pdf How can one visualize a multi-periodic pulsation or oscillation?
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79 views

Why does the classical electrodynamics Lagrangian density equation have a “field” term and an “interaction” term?

On Wikipedia's page on classical electrodynamics, they state the Lagrangian density equation as follows \begin{equation} \mathcal{L} = \mathcal{L}_{\text{field}} + \mathcal{L}_{\text{int}} = ...
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96 views

Kinematic Viscosity

How would you define kinematic viscosity? What does it physically represent? Around the Internet I've found it defined as just a ratio, and that's it. I saw in an answer that I can think of it as ...