The definition tag is used in situations where the question is either about how some term or concept is defined or where the validity of an answer depends on a subtle definition of some term or concept used in the question.

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What is meant by potential energy for a particle in a field?

Potential energy is usually defined using a field and a particle that experiences the field force, as the work down in moving a unit particle from infinity to a position in that field. But some ...
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1answer
208 views

What are “cycles of anomaly” and “cycles of longitude”?

In several early (pre-1600) astronomical texts I read about "cycles of anomaly" and "cycles of longitude", but it us unclear to me what these terms mean. They were clearly familiar to authors at the ...
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2answers
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Does a cycle (in Simple Harmonic Motion) have to equal 2π?

So, I search for the definition of cycle and I get this in Wikipedia: A turn is a unit of angle measurement equal to 360° or 2π radians (or ...). A turn is also referred to as a revolution or ...
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1answer
50 views

Scientific definitions of “moment (of)” and “instant”? [closed]

What are the scientific definitions of "moment (of time)" and "instant"? Are they different with their definitions in everyday language? I also don't know the definitions in everyday language, of ...
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1answer
57 views

Definition of Charge [duplicate]

Please give me a definition of charge. A textbook I have defines it to be - "A fundamental property of matter, which determines whether the matter will receive an electric flow or liberate one" I don'...
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1answer
336 views

Is displacement in circular motion a chord or an arc?

When taking the displacement between two points along a circular path to calculate its velocity, do you take the length of a chord connecting the two points or do you take the length of the arc ...
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1answer
60 views

What's the difference between the Fermi level and the electrochemical potential?

I was asked in a Thermostatistics test to compute the electrochemical potential $\mu(T)$ and the Fermi level $\epsilon_F$ for a system of non-interacting fermions, with two possible energetic states ...
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1answer
146 views

What is the defintion of a current-current diagram?

Right now I am facing some Feynman diagram calculations and in the instructions I am reading the phrase current-current diagram appears quite often so I wanted to know: What is the definition of a ...
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1answer
209 views

What exactly is a one particle density?

In Density Functional Theory (DFT) we derive the Grand Potential as a functional of a so-called one particle density (OPD). I have trouble imagining what exactly that is. Could someone help me with ...
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2answers
144 views

Can pressure be negative? [duplicate]

From Wiki and from physics fundamentals lections I received info that pressure is scalar value. But in definition you have relation between projections of two vector values to normal axe-force and ...
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1answer
187 views

What is the definition of 'relative population' in context of partition function?

In statistical mechanics, what is the definition (or mathematical definition) when authors refer to relative population in the case of a classical particle system?
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1answer
871 views

Conventional definition of ideal fluid

According to Landau&Lifshitz, an ideal fluid is one with zero viscosity and a negligible thermal conductivity. This is also the FR.wikipedia version: En mécanique des fluides, un fluide est ...
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1answer
184 views

What is thermodynamic equilibrium?

The state of thermodynamic equilibrium is typically defined referring to the system's behaviour in the future. Can the definition be formulated in terms of measurable quantities?
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1answer
228 views

Definition of Entropy for reversible and irreversible process

$\int \dfrac{\delta Q}{T}$ can't be used to calculate entropy of an irreversible process. If you happen to know heat supplied and temperature at which it is supplied for just an instant. Can you then ...
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1answer
94 views

Strange definition of a two-level system by the Bloch vector

A two-level system can be described by a density operator involving the Bloch vector $$ \vec{r}; \quad r_x = Tr(\rho X); \quad r_y = Tr(\rho Y); \quad r_z = Tr(\rho Z) $$ as $$ \rho = \frac{I + \...
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1answer
60 views

What is the relationship between the verbal definition and the mathematical definition of some quantities?

I know this is probably an easy question, but it's been a while since I've studied physics and I've started reading some circuit analysis textbooks. I'm finding hard to understand the relationship ...
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1answer
80 views

What is Work? What does the quantity suggest intuitively? [duplicate]

The mathematical formula for work says that work is force into displacement, but what is the philosophy behind it? I mean what does the quantity suggest?
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1answer
459 views

Null lines and degenerate plane

Can anyone explain me what null lines are and degenerate plane? I don't know anything about it, I don't have physics background and I am a mathematics student and please tell me if there is any good ...
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2answers
1k views

Clarification regarding Newton's Third Law of Motion and why movement is possible [duplicate]

Newton's third law states that to every action, there is an equal and opposite reaction. If that's the case, then how do things move at all? Shouldn't all applied forces be canceled by the equal and ...
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1answer
121 views

A sphere, a simple object?

In this video, the woman says that a sphere is a pretty simple object. What intrigues me is the use of a sphere for such a calculation. First of all, the sphere wouldn't be perfect as a perfect sphere ...
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1answer
381 views

Tensors: relations between physics and linear algebra

In continuum mechanics we use finite deformation tensors to exprime deformations in a point. The 9 components of the tensor (in reality 6 because of its symmetry) are defined as $$ \sigma_{ik}(\vec{r})...
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3answers
28k views

Difference b/w Kinetics & Kinematics w/concrete example

(I know whether I understand this or not doesn't matter much to my work & study but am just curious.) I still can't differentiate in my head kinetics and kinematics (similar thread is found but ...
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1answer
214 views

Reality constraint

What is the "definition" of a reality constraint and why is it called that way? (I mean how it is used for example in quantum field theory and string theory)
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0answers
63 views

What is difference between variations of the work and virtual work?

I really want to know whether or not both equations are the same mathematically. I think that they are the same, I just want to be sure. (Reference: this website.)
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LHCb Peaking Background

I was reading a paper on the estimation of the branching fraction of B+ to K pi pi gamma. I was wondering whether you could clarify the meaning of peaking background. Thanks!
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0answers
27 views

Is there a standard in the manner in which significant figures are used?

I have always understood significant figures to be those figures which we know with certainty. Wikipedia (https://en.wikipedia.org/wiki/Significant_figures) provides a related but less rigid ...
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0answers
63 views

Definition of heat that does not produce a cyclic argument?

If we are going to define (empirical) temperature from the zeroth law, we need a definition of heat that does not depend on the concept of temperature, else this would produce a cyclic argument. ...
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0answers
38 views

Definition for a trajectory in phase-space

When we say "a trajectory in phase space", when the parameter is time, do we mean the set of points in phase-space corresponding to a continuous segment in time? Does it have to be continuous? Does it ...
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0answers
36 views

What is the general definition of a quench?

I've seen the term "quench" used in many different contexts. It's easy to understand the meaning when the context has a simple physical analogue, such as lowering the temperature of a system to cause ...
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2answers
60 views

How can you tell if the work done by a force is negative?

This is kind of confusing to me. I'm guessing that it's specific to the problem. Is the work done by friction always negative? Is the work done by gravity always negative? Spring as well? It seems ...
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0answers
44 views

Is the formula of temperature $ \frac{1}{T}= \left(\frac{\partial S}{\partial U}\right)_{V,N}$ applicable to all type of ensembles?

I have seen multiple posts on this page that explained the statistical definition of Temperature as the derivative of the Entropy to the energy: \begin{equation} \frac{1}{T}\equiv \left(\frac{\...
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1answer
82 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
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1answer
79 views

What constitutes a force? [duplicate]

There are a few questions on here about why Gravity is not a force, but I'm having trouble grasping why exactly. It sounds to me that Gravity is not a force because it is simply a by-product of mass ...
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2answers
1k views

Can we define tension in a string as the reactive force produced in a string being pulled at both ends?

In my textbook, the definition of tension was given that Tension is the reactive force which exists when string is being stretched at its both end. After it there was a case given that to calculate ...
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80 views

What's the difference between “spectromicroscopy” and “microspectroscopy”? [duplicate]

Both definitions that I found are rather vague. (Related question: What's the difference between microscopy and spectroscopy?)
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61 views

Are there universally accepted definitions for physics concepts? [closed]

Is there a list of definitions that have been agreed on by physicists so that everyone's understanding of a term is approximately the same? I have been reading some basic books and they usually give ...
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1answer
97 views

Defintion of temperature without thermal equilibrium condition

Is temperature only defined in thermal equilibrium? Then how can we explain heat flow by temperature differences?
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1answer
111 views

What does degrees of freedom mean in the context of vibrations?

If you have an $N$ degrees of freedom system what does this mean? What is the difference between a 1 and a 2 degrees of freedom system?
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1answer
225 views

Defining creation and annihilation operators

Creation and annihilation operators can be defined in several different ways, some more general than others. We usually choose to denote by $a$ the annihilation operator and by $a^\dagger$ the ...
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Should Brillouin zone be a continuous object rather than a discrete one in the thermodynamic limit?

For example, just consider a 1D atom chain with $N$ sites and lattice constant $a=2\pi$, under periodic boundary conditions, the crystal momentum reads as $k=\frac{n}{N}\frac{2\pi}{a}=\frac{n}{N}$, ...
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1answer
238 views

Second Rank Tensors [duplicate]

I'm a little confused, for the twentieth time, on what tensors are. I thought they were a generalization of matrices-but then they have special transformation rules. I'm looking for a concise ...
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0answers
585 views

How is the term “Born level” usually defined?

How is the term "Born level" usually defined, e.g. in talking about the $pp\to Z/\gamma^*\to e^+e^-$ cross section at Born level?
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1answer
124 views

Two definitions: 'semi-classical space-time' and 'supersymmetric Minkowski space'

By reading articles I ran several times into two terms, never being defined so I assume they must have well established definitions somewhere. The first is semi-classical space-time. If I where to ...
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5answers
671 views

Are events in this experiment simultaneous if observed in platform's frame?

In some contexts e.g. on Wikipedia it is defined as a matter of happening . In others(e.g. as defined by Einstein in his book "Relativity the special and general theory") it is defined as a matter of ...
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6answers
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Why do we use capacitors when batteries can very well store charges?

Can batteries be used instead of capacitors? I am trying to figure out a basic, superficial and any obvious difference between the two.
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1answer
243 views

Can we call every pure solid a crystal?

What are pure solids? How many types of pure solids do we have? Are we still finding new pure solids or are these pure solids limited in number?
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2answers
165 views

Definitions of Lagrange points: $L_4$ and $L_5$

We have the the five Lagrange points (let consider Earth and Sun): $L_1$ - lie between Sun and Earth; $L_2$ - beyond the Earth; $L_3$ - beyond the Sun; And what's the difference between $L_4$ and $...
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2answers
205 views

How many psi's are in one bar?

6894.7573 bar = 100000.0 psi according to google 6894.7573 bar = 100000.0001 psi according to wolfram alpha which is it? How many psis are in one ...
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2answers
73 views

SI Base Unit definition of mass - obsolete?

According to the formal definition of the SI Base unit of mass, the kilogram, it is stated that "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the ...
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Is this definition of work right?

My thermodynamics textbook defines work as follows. Work is motion against an opposing force. But this definition of work doesn't imply that work is done in accelerating a body does it? So is ...