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

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2answers
45 views

SHM with acceleration at mean position

Suppose we have an equation of motion as $$\frac{d^2x}{dt^2} = -kx + c,$$ then can it be called a SHM? Since acceleration is still proportional to displacement. But then, how will we define the mean ...
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2answers
93 views

Why is it called “escape velocity” and not “escape acceleration”?

As we know, velocity to escape from an orbit is in proportional with the orbital velocity: $$v_\mathrm{escape}=\sqrt{2}v_\mathrm{orbit}$$ Since, orbital velocity decreases as we move away so should ...
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2answers
131 views

Is escape velocity really a velocity (rather than a speed)?

The term escape velocity is quite common to us. But we know velocity is a dimension dependent on the direction. But the escape velocity has same value irrespective of from where it is thrown from the ...
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2answers
79 views

What exactly is duality?

I came across the notion of duality recently to explain a physical concept. What is duality? Why does it occur? How do I know if two things are dual?
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1answer
52 views
15
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6answers
1k 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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1answer
186 views

Where can I find the equations for “quasi” elastic collisions?

Yes, you all talk about neutrinos and spins, but I came out with this basic s**t :D All of us learnt the basic equations of collisions, elastic (everything bounces and energy remains the same), or ...
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1answer
56 views

What does it mean to say that something is “relativistic for an electron”?

I want to understand a concept better. I did a homework problem where I solved it all the way, then checked my answer with a solution set. My answer was different, so I followed the solution set from ...
4
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1answer
69 views

In GR what is a “source-frame mass”?

In the recent LIGO paper, "GW150914: First results from the search for binary black hole coalescence with Advanced LIGO, (LIGO Scientific Collaboration and Virgo Collaboration)", they refer to the ...
3
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1answer
231 views

How did neodymium magnets get their name?

Like in the question. Why neodymium magnets (Nd2Fe14B) are called "neodymium magnets"? Why not boron magnets? Or iron magnets?
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1answer
53 views

Energy method to solving equations of motion? Why does this method work and what is it called?

Given the stated system in the photo we are suppose to prove simple harmonic motion when given an initial displacement $x$ I first considered the total energy of the system which we will call $H$ $$...
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1answer
2k 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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3answers
2k views

Why is density an intensive property?

I am still trying to understand what are intensive and extensive properties. Possibly someone can give a pointer to a decent text (preferably on the web), as I am not too happy (to say the least) with ...
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2answers
135 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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1answer
73 views

Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= 26....
3
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1answer
270 views

Why is the projective symmetry group (PSG) called projective?

As discussed by Prof.Wen in the context of the quantum orders of spin liquids, PSG is defined as all the transformations that leave the mean-field ansatz invariant, IGG is the so-called invariant ...
1
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1answer
885 views

Brightness of light sources

I would like to know what determines the brightness of light. I'm confused, After hours of reading, I got these definitions mixed up I need to link them together: Light intensity Brightness of ...
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0answers
42 views

Name of the fourth entropy potential

Wikipedia's "Free Entropy" page lists three entropy potentials: Entropy, $S$, with natural variables $U$ and $V$ Massieu Potential / Helmholtz Free Entropy, $\Phi$, with natural variables $1/T$ and $...
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0answers
36 views

Why is Bohr's explanation called Bohr's model and not Bohr's theory?

I have seen an answer which tells the difference between model (specific) and a theory (general). And it makes sense 'coz Bohr explained it for the hydrogen atom only. But did he not make a set of ...
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2answers
78 views

Is standing wave realy a wave [closed]

We know that at least the waves inside a flute or laser make resonance waves,and simply we know that a standing wave is superposition of two waves that are propagating in oposit direction,for example ...
2
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2answers
111 views

What does naturally mean here?

We often cross the sentence "Kahler geometry emerges naturally in sugra". I have always wondered what does this mean; actually what does naturally mean in that sentence?
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0answers
78 views

What is a Witten diagram?

Recently I heard the terminology of Witten diagram. Studying QFT, I frequently see Feynman diagrams and use them to compute scattering amplitudes, one-loop corrections and so on. In string theory ...
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1answer
84 views

How is father of physics appointed? [closed]

I've tried Google, but couldn't figured out exactly whether its Newton, Einstein or Galileo. What is the criteria for appointment of father for a particular subject?
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5answers
827 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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1answer
119 views

What does $L^2(S^1,\mu_H)$ mean?

It's a Hilbert space, $\mu_H$ stands for the Haar measure on $U(1)$, but what does $S^1$ mean? I found it in one of my quantum mechanics books which approaches from a very 'mathematical' way.
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1answer
39 views

How do we call in English scientific terms the Fermat's principle about back and forth light traversal?

We know that the path followed by the light from point A to point B is independent of the direction of propagation of light. This is what is called in French "le principe de retour inverse de la ...
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4answers
58 views

Same equation, different meanings

I went into a physics classroom today and saw this equation written on the board: $$ E = \frac \sigma \epsilon $$ At first I thought it referred to the electric field $ E $ between 2 parallel plates ...
3
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1answer
86 views

What does “sites” mean in the lattice language?

I acknowledge that this question is quite trivial. But in the lattice jargon, what does a $N$-sites lattice mean? it's a lattice $N\times N$ or it's a lattice with $N$ vertices? another option ...
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4answers
145 views

What is meant by an excited atom?

I want to know how an atom is when it is excited. If an atom, due to collision of another fast moving atom, becomes fast moving as well, is that also an "excited state"?
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0answers
93 views

Which scientist is this?

Okay so I was watching discovery channel, in that i saw a man cleaning live electric wires of 10k volts in the air, he was not touching the ground. They said he was able to do this because of the "law"...
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1answer
86 views

Doesn't linear motion include curvilinear and rectilinear motion?

From some Portuguese language textbooks, I learned the following definitions: linear motion (movimento linear): motion along a line; rectilinear motion (movimento retilíneo): motion along a straight ...
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0answers
53 views

Terminology - optical (visual) properties of a structure

I am trying to understand few terminological problems that I encounter. Without knowing keywords it is hard to perform search for literature or publications in the area. The area relates to the ...
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3answers
62 views

What is the difference between accelerating and boosting?

My professor claimed in class that there was a difference between an acceleration and a boost. I don't really understand the distinction. If you want to go to a different inertial frame of reference, ...
3
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0answers
46 views

What is $\mathrm{U(1)}$ vector and axial?

In hadron physics we talked about $\mathrm{U(1)_V}$ (vector) and $\mathrm{U(1)_A}$ (axial) as well as $\mathrm{SU(3)_L}$ (left) and $\mathrm{SU(3)_R}$ (right). There are certain relations between them ...
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1answer
34 views

Prompt gamma emission vs gamma decay

I understand prompt gamma emission to mean gamma emission in a time period shorter than a second. I understand gamma decay to be the relaxion of a nucleus into a lower energy level by emission of a ...
3
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1answer
167 views

Repeated index in covariant derivative using abstract index notation

The same index showing up twice in the charge conservation law $\nabla_a j^a = 0$, as stated using abstract index notation, highly confuses me. If we chose a coordinate basis $\{\partial_\rho\}_{\...
2
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1answer
220 views

When was the first time that superconducting quasiparticles were called Majorana fermions?

Since a number of years, the field of superconductivity has a growing obsession with Majorana fermions. I wonder how far back we can go: When was the first time that superconducting quasiparticles ...
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4answers
41 views

What is the distinction between a “ray” and a “wave” in optics?

What is the distinction between a ray and a wave in optics? From what I can gather, the only discernible difference is in nomenclature, where a ray simply refers to an EM wave with short wavelengths. ...
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2answers
96 views

Distinguishing real forces and fictitious/pseudo forces in Newtonian mechanics

In understanding the law of inertia I had to consider the motion of bodies screened from the so called "real forces". What characterises these real forces? What makes us call them real? Or what is ...
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1answer
490 views

Does the Sun “drag the solar system through space”?

In this video: http://www.youtube.com/watch?v=0jHsq36_NTU#t=55 at 0:55, it is claimed that "the sun is [...] dragging the planets in its wake". Is this true? My understanding is that the sun and ...
1
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3answers
129 views

What does “fidelity” mean?

In particular I am interested in whether it is more closely related to "precision" or "accuracy". So a somewhat mathematical description might be appropriate. For example the word "fidelity" occurs ...
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0answers
41 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 ...
2
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3answers
643 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
39 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
1k 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.
2
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1answer
56 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 ...
1
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1answer
367 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 "...
3
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4answers
107 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 ...
0
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1answer
43 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 ...