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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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Physics terminology: Can a light beam be displaced?

Say you have a rotating mirror and a fixed laser beam pointed towards the mirror such that the reflection of the beam changes direction. Can you say that the light beam has been displaced? Why or ...
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Why is the ångström not a metric unit? And why is the ångström spelt with the Scandinavian letters “å” and “ö”?

The website here http://unitsofmeasure.org/ucum.html tells us whether every unit is metric or not. Metric units can be multipled by a power of 10 and can be combined with a prefix. 1 ångström is ...
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Is there a noun for a material that absorbs, scatters and luminesces?

I know Luminophore is used for molecules or nanocrystals which absorbs and emit light, and Scatterer is used for materials which scatter light (elastically or inelastically). I suppose it would be ...
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1answer
28 views

What is the difference between scattering and absorption/emission?

As far as I know, scattering occurs when light excites the atoms or molecules to their higher energy state(virtual state for scattering) followed by emitting photons corresponding to energy ...
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Nomenclature for Lagrangian of system with rotational and translational motion

i am trying to wrap my head around how you would go about writing the euler-lagrange equation for a system with both translational and rotational motion. It is for calculating the response of the ...
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40 views

Kinematics: Circular Motion

What is the difference between angular velocity and angular speed? Is angular velocity after one complete rotation zero? Is the magnitude of angular velocity always equal to angular speed?
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25 views

Elongation of a simple pendulum

One of the questions on this weeks question sheet asks for the maximum elongation of a simple pendulum. The pendulum is set in motion on the moon with f = 0.5Hz. What is meant by the elongation of the ...
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9 views

Use of “rate function” as rate over density

Heggie (1975) uses the term rate function to express the ratio of the rate $R$ of some event (for example the dissociation of a given binary star by the interaction with a passing field star) with the ...
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73 views

What is the External force? [closed]

In a vacuum, a uniform electric field of strength $E$ is applied in the positive x-axis direction. When you carry a charged particle with a positive charge $q$ from $A$ to $B$, seek the work that the ...
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1answer
32 views

Difference between discharge tube and capacitor

I did search this on google but didn't get satisfactory results. Can you tell me difference between capacitor and discharge tube? "**Discharge tube has its gaseous medium at very low pressure but ...
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1answer
29 views

What is meant by homogeneous in $x$ in $n$'th degree?

I'm reading about classical mechanics by Goldstein, and in the section about Hamiltonian mechanics it is stated that in the expression: $$H(q,p,t)=\dot{q}_ip_i-L(q,\dot{q}, t)$$ the Lagrangian ...
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Complex numbers in physics [duplicate]

Can someone please explain the origin of complex numbers in physical values. For instance, denoting a plane wave with Euler's identity and also the complex relative permittivity? Thank you.
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What is a quantum system?

I heard that a wavefunction applies to a quantum system. But what is a quantum system? I am new to quantum mechanics, sorry for asking a basic question.
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The difference between exact solution and analytic solution

My mother tongue is not English so I am confused with the difference between exact solution and analytic solution. Are these the same?
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1answer
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What is a free parameter?

Soft question here, but I was wondering just what exactly free parameters are? I have a murky understanding on the concept but I would much appreciate someone shedding some light on the matter. Is ...
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1answer
142 views

When should we consider “reverse Heisenberg” evolution of operators?

In Quantum Mechanics, the Heisenberg evolution of an observable $\hat{o}$ is defined as $$ \hat{o}(t) = U(t,0)^{\dagger} \hat{o} U(t,0) $$ where $U(t,0)$ is the unitary time-evolution operator from ...
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How is do you say the “standard acceleration of gravity, $g=9.80 m/s^2$” in words? [closed]

How is do you say 9.80 m/s^2 in words? (I Don't get if only "the second" is squared or the whole thing is squared or just the m/s is squared)
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Why is the 1-dimensional wave equation called like that when it seems to be 2-dimensional?

The wave equation in one dimension traveling along a string is: $$ \frac{∂^2y}{∂x^2} = \frac1{v^2} \frac{∂^2y}{∂t^2} $$ but this equation has 3 variables $x, y,$ and $t$, shouldn't it be in 2 ...
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In particle physics, how should we call a model with several Higgs boson : Higgs multiplet?

In Higgs physics of the Standard Model, there is only one Higgs. The Higgs belong to a Higgs doublet. After electroweak symmmetry breaking, there is only one remaining Higgs, and 3 Goldstone bosons. ...
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1answer
34 views

What's the name for “middle” principal axis of inertia?

See this question for some context about the stability of rotation of a body around different axes. I am now trying to say that the rotation around the middle axis is very unstable, without using ...
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1answer
39 views

What does topologically stable mean?

I am working on an article about skyrmion manipulation and it is written that those particles are "topologically stable particle-like spin configurations that carry a characteristic topological charge ...
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1answer
66 views

Feynman screwjack problem

What is a thread? How does he know you need to turn the handle "around" 10 times? From where does the 126 inches come from? I thought Feynman explanations were easy... Let us now illustrate the ...
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1answer
48 views

Noun for particles that are quantumly entangled

What will we call particles that are in a "quantum entanglement" kind of relationship? not looking for examples (like thingamatrons can participate theoretically in quantum entanglement); rather the ...
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2answers
48 views

Fermat's Principle: no first-order change in time?

I was reading the chapter on Fermat's principle in the Feynman lecture series. The principle is stated along these lines: "The correct statement is the following: a ray going in a certain ...
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What is recessional nonlocality?

In laymen’s terms, what is recessional nonlocality? I understand recessional means to recede or retract away, and (correct me if I’m wrong) I understand locality has something to do with quantum ...
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1answer
74 views

What are $U(n)$ or $\mathbb{Z}_2$ quantum spin liquids?

Quantum spin liquid is a state of matter in which spins are correlated and fluctuate even at zero temperature. My question is about these terms in general. When we say that a state or a quasi-...
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1answer
60 views

What is a rigid wave function?

The London equations prior to BCS that describe superconductivity require assuming the wavefunction describing the superconducting pair of electrons to be rigid. I've been looking all over trying to ...
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1answer
47 views

Method of Dimensional analysis: What does “an expression of product type” mean?

I read in the book Concepts of Physics by HC Verma in the section of Limitations of Dimensional analysis that the method of dimensions cannot lead us to the correct expression sometimes if expression ...
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2answers
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Area under a velocity graph

If I took the definite integral of a velocity graph from 0 to 10 seconds, the answer would be the change in position over those 10 seconds correct? I am told by my teacher the area is change in ...
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Inclusive jets and forward jets

In several studies of experimental particles physics, I find that a process distributions of a given observable are divided into categories such as "forward-jet", "inclusive-jet" and zero-jet". I can'...
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Name for the set Displacement, Velocity, Acceleration, etc

Is there a name for the set Displacement, Velocity, Acceleration, Jerk, etc? The only name I can think of is 'Derivatives of displacement (wrt time)' which is rather long.
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Is there a name for this dimensionless quantity?

I have an equation with the nondimensional number $\Delta P L / \sigma$. Here $\Delta P$ is a characteristic pressure drop, $L$ is a characterictic length, and $\sigma$ is a characteristic surface ...
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Is there a word for the availability of a gas, normalized for pressure?

As a bit of background of what I'm getting at, consider that for the purposes of humans breathing and getting oxygen into their blood, 20% oxygen at 1 atm is equivalent to 100% oxygen at .2 atm. ...
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1answer
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Einstein solid degree of freedom

I was studying from Schroeder's thermal physics book. When it talks about Einstein solids it says that they have 2 degrees of freedom thus $U=NkT$ However, I thought when we talk about Einstein ...
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2answers
58 views

What is meant by “linear” in non-equilibrium thermodynamics?

I'm trying to learn a bit about non-equilibrium thermodynamics, and am currently reading de Groot and Mazur. In it, there is a quote right in the beginning, talking about the phenomenological ...
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1answer
34 views

Difference between time series and trajectory terminology

What is the difference between trajectory and time series? To me both seem the same thing. In the 3D diagram (cube picture on left of Fig.2 from the paper titled “Review and comparative evaluation of ...
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2answers
96 views

Why is particle physics called high energy physics? [duplicate]

The highest energy accelerator till date is the LHC which operates at an energy scale of perhaps 10-100 TeV. In SI units this is about $\sim 10^{-6}-10^{-5}$ Joule which is several orders of magnitude ...
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Technical question on definition of free fall

Free fall is any motion of a body where gravity is the only acceleration acting upon it. But, what if I threw an object from a certain altitude, and had two jetpacks put on it , one providing ...
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What does 'per unit frequency' refer to?

We were discussing Kirchoff's theorem on blackbody radiation in class today and the equation was: $$e_{f}= J(f,T)$$ $e_f$ was defined as power per unit area per unit frequency. What does per unit ...
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1answer
75 views

What's the difference between canonical quantization and second quantization?

I am wondering the difference between the canonical quantization and the second quantization in quantum field theory. For example, a harmonic chain, one can write down its lagrangian density $\...
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2answers
95 views

$n$-body problem = many-body problem? [closed]

Are the terms "$n$-body problem" and "many-body problem" synonymous? Or does one refer to a numerical problem an the other to an analytical problem?
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Reversed effective force in D'Alembert's Principle [duplicate]

In D'Alembert's Principle,what is reversed effective forces and how to determine it's direction?
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1answer
64 views

What is the difference between degree celsius and celsius degree? [duplicate]

It seems similar but can you guys please answer it that what is a specific difference between degree celsius and celsius degree?
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What is the static exchange approximation?

In this paper, on the 4th page (and throughout), they talk about studying electron-helium scattering in the "static-exchange approximation". I have scoured the literature and have not been able to ...
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1answer
72 views

Terminology for time derivative of speed (not velocity)

Is there any standard terminology for the derivative of the magnitude of velocity with respect to time (suitable for use in first-year Calculus)? The word ‘acceleration’, in its technical sense, is ...
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4answers
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Is the notion of 'weight of Earth' meaningless?

I am not talking about the distinction between mass and weight, just the concept of 'weight'. In University physics (book by Young & Freedman, 14th Ed.) it is given that the weight of an object ...
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3answers
55 views

Is a rotating object moving or stationary?

Because it rotates in situ, its center of mass does not move, so it is static, but it is rotating, so it is not static, then is it static or moving?
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Is the designation “chemical reaction” right for vibrational and electronic excitation of particles?

I'm currently doing my Master's thesis, which focuses on Atmosphere Reentry Thermodynamics and Kinetics. Due to the importance of this work, I would like to use the best terms to describe any ...
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1answer
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If we say “an object is at rest,” can we also say “the object is moving at a constant velocity?” [closed]

If we say "an object is at rest," can we also say "the object is moving at a constant velocity?" Of course, the constant velocity would be zero, so it's mathematically sound. However, the wording ...
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What “luminosity distance” means in a general spacetime?

In the paper "Asymptotic Symmetries in Gravitational Theory" by R. Sachs from 1962, the author says the following: In analyzing gravitational fields it is sometimes useful to introduce coordinates ...