# Questions tagged [terminology]

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

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### What's the difference between linearly polarised and plane-polarised waves?

To explain polarisation, my book gives an example of a transverse wave in a string, and explains as: Since each point on the string moves on a straight line, the wave is also referred to as a ...
449 views

### Difference between yaw angle and slip angle

What's the difference between slip angle and yaw angle (speaking about cars)? It seems they both are the angle between the actual direction of travel and the direction towards which it is pointing.
3k 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?
20 views

### Latent Heat and Ordinary Heat?

We have a name for the thermal energy associated with the change of potential energy during a phase transition. Unless I'm very mistaken, we call this latent heat. Here we have $Q=mL$. But what ...
158 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 ...
52 views

### What's the difference between repulsive Delta function and Attractive Delta Function?

What's the difference between repulsive Delta function and Attractive Delta Function? I need to clear the concept. Please note that I know what's the Delta function.
212 views

### What's the difference between a time crystal and a system undergoing periodic motion?

What's the difference between a time crystal and a system undergoing periodic motion? My understanding of a crystal is that it is a rigid body with a spatially periodic structure. Is any system ...
169 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 ...
206 views

### Tensors defined by transformation laws are tensors at a vector space or tensor fields?

In Physics it is common to see tensors defined by transformation properties relating components of the object in different coordinate systems. There is, however, two ways we can think of a tensor: a ...
117 views

### Constants of Integration In Hamilton-Jacobi theory

I have had this confusion for a while now. We solve the Hamilton Jacobi equation, $$H+\frac{\partial S}{\partial t}=0$$ Say we get a solution $S(q,\alpha,t)$ where $\alpha$ is a constant of ...
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### How does the term “time-integrated flux density” apply to the effluence of a stream of atoms on a surface?

I just edited this answer to read Kapton (again from SMAD), will degrade at a rate of 2.8 μm for every $10^{24}$ atoms/m$^2$ of atomic oxygen time-integrated flux density encountered, with silver ...
76 views

### Is there a name for the unit “Ampere meter”?

Motivation: I'm doing a homework problem involving a rod sliding freely down a pair of parallel conducting rails. I've got a quantity of unit $\mathrm{A \cdot m}$ and want to know what I should name ...
38 views

### Is there any synonym to the “flaring out condition” of travesable wormholes?

Given the knowledge of Einstein Field Equations, the one could ask if it is possible to connect asymptotically regions of a given spacetime, such that a time-like curve is possible to transit between ...
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### Historical meaning of action

In the Feynman lectures, it is stated Also, I should say that $S$ is not really called the ‘action’ by the most precise and pedantic people. It is called ‘Hamilton´s first principal function.’ Now ...
35 views

### 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 ...
43 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?
109 views

### 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 ...
12 views

### 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 ...
526 views

### Does effective theory have the same meaning in particle and condensed matter physics

I have a naive question about the meaning of effective theory in particle physics and condensed matter physics. In particle physics, from what I know, the effective theory comes from the Wilsonian ...
2k views

### What is the difference between the meaning of “state space” and “configuration space”?

What is the difference between the meaning of "state space" and "configuration space"? I'm only familiar with the first, and when I look up the second I can't tell the difference.
34 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 ...
150 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 ...
381 views

### The meaning of covariant but not manifestly covariant

What is the most general meaning of the expression covariant, but not manifestly covariant? Suppose I have a general (local) change of coordinates, $x^{\prime} = f(x)$, on an $(n+1)$-dimensional ...
39 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 ...
6k views

### The instant an accelerating object has zero speed, is it speeding up, slowing down, or neither?

This problem is from Khan Academy. Specifically for the blue point circled in red, the answer is that at this blue point, the object is neither speeding up nor slowing down. When I think about the ...
10 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 ...
3k views

### Difference between homogeneous and uniform?

Homogeneity means that something is the same in every point in space, whereas isotropic means that there is no directionality. Uniformity implies there is "no variation". But what is actually the ...
44 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 ...
80 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 ...
340 views

### What's the relationship between probability amplitudes and amplitudes of a wave?

Amplitudes or probability amplitudes are the complex coefficients of the linear combination of states which represent other quantum physical states. The amplitude of a wave can be interpreted as a "...
88 views

### 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.
338 views

### Classification of field types in QFT

In Classical Field Theory fields are sections of bundles over spacetime. In particular we almost always consider vector bundles. Some examples are: Scalar fields: these are sections of the trivial ...
150k views

### What exactly is the difference between radiation, conduction, and convection?

Okay, so everywhere I've read, I hear the main difference is the requirement of a medium. But for example, if you take the case of heat 'radiating' from a red-hot iron, isn't that actually convection ...
45 views

### 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?
211k views

### What is the difference between phase difference and path difference?

The path difference is the difference between the distances travelled by two waves meeting at a point. Given the path difference, how does one calculate the phase difference?
36 views

### 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 ...
113 views

### 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 ...
22 views

### 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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### 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 ...
68 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 ...
50 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 ...
52 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 ...
53 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 ...
322 views

### Friction force in rolling motion

In rolling without slipping motion we know that the friction acting is static friction and so we treat it as an unknown while solving equations of dynamics. Question: Is the static friction during ...
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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 ...
441 views

### What is the linear attenuation coefficient and how does it relate to interaction probability?

I have misunderstanding the linear attenuation coefficient (L.A.C) concept. As known, L.A.C is depend on absorbed medium and energy of incident radiation. Supposing, L.A.C= 100 cm-1, how can this ...
94 views

### What is *diagonal* long range order?

I have seen this question about off-diagonal long range order in superfluids. What’s the difference and the significance between long range diagonal and off-diagonal long range order?