The definition tag is used in situations where the question is either about how some term or concept is define 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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1answer
83 views

Transpose of (1,1) tensor

When we transpose a (1,1) tensor, shall we simply switch the two indices while keeping their upper/lower positions or switch them and also switch their upper/lower positions? In general, would the ...
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2answers
220 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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4answers
50 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
168 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
83 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
122 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
65 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
7k views

Difference between angular frequency and angular velocity?

What is the difference between angular frequency and angular velocity? I think one is used for SHM and the other for circular motion? Also can both be used for centreptal accelartion? I think angular ...
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1answer
52 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
66 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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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
125 views

A physical sense of an Inertial frame

Definition clarification needed, please: I am hoping to get physical sense of an "inertial frame". Do inertial reference frames all have zero curvature for their spacetime? So is an inertial frame ...
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1answer
103 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
337 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 $$ ...
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1answer
168 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
65 views

How is Infinitesimal coordinate transformation related to Lie derivatives?

I am reading the book "Gravitaion and Cosmology" by S. Weinberg. In section 10.9, while discussing Lie derivatives of tensors of different ranks, he makes a general comment: The effect of an ...
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0answers
48 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
71 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
39 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
133 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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0answers
70 views

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
151 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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1answer
2k views

Why is the mechanical advantage of a wedge = length of slope/ width?

Mechanical advantage is defined as Force Output/Force Input For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, the articles ...
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0answers
1k views

Definitions in thermodynamics: temperature, thermal equilibrium, heat

I'm currently reading Fermi's "Thermodynamics" and I'm trying to grasp the (possibly different) right definitions for temperature, thermal equilibrium, heat. To clarify, I'm looking for definitions ...
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0answers
458 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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0answers
85 views

Motivation For Definitions [closed]

I noticed in my physics textbook that we define certain relationships to be true. I can see how this is considerably helpful in deriving other relationships from these definitions; for instance, take ...
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1answer
117 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
443 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
137 views

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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2answers
148 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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3answers
168 views

Is my conceptual understanding pertaining to heat & temperature correct?

From what I've understood: Heat is the total sum of translational energy possessed by individual atoms in an object. Temperature is the average translational energy possessed by individual atoms ...
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2answers
103 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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3answers
3k views

Differences between wavefunction, probability and probability density?

I am trying to understand the differences between wavefunction, probability and probability density. There are different definitions on the internet. For example: ...
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2answers
13k views

Definition of electric charge and proper explanation

Is there a definition of electric charge and proper explanation of it? It is said "Electric charge is the physical property of matter that causes it to experience a force when close to other ...
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3answers
107 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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2answers
68 views

When momentum coincides with impulse

If an object is pushed for some time by some force from a resting state, can I say that at the exact moment the force is removed, impulse equals momentum?
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1answer
112 views

Definition: Coupling [closed]

What does it mean to say that 2 fields are coupled? More generally, what does "coupling" mean?
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2answers
75 views

Is electric potential a form of potential energy?

As I understand it, the concept of potential energy arises from analytical mechanics. Yet I often see the concept of electric potential $\phi$ introduced without mention of analytical mechanics. For ...
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1answer
60 views

It seems wrong to find the mass using weight alone when using chemical compounds [duplicate]

The difference between mass and weight is pretty straightforward so then how can we WEIGH a substance then ask how many Daltons (atomic MASS units) are in that substance without a conversion in there ...
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1answer
1k views

Distinguish between instantaneous speed and instantaneous velocity

I encountered a line in my text book of physics that: Average speed over a finite interval of time is greater or equal to the magnitude of the average velocity. But instantaneous speed at an ...
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1answer
63 views

How are these two Riemann tensor equations equivalent?

Poisson in A Relativist's Toolkit defines the Riemann tensor as$$A_{\,;\alpha\beta}^{\mu}-A_{\,;\beta\alpha}^{\mu}=-R_{\phantom{\mu}\nu\alpha\beta}^{\mu}A^{\nu}.$$ Foster and Nightingale's A Short ...
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1answer
39 views

Integral limits when calculating the work

If I integrate $$dW= \vec{ F} \cdot d\vec{\ell}$$ which are the limits? In $$\int\limits_{W_{inf}}^{W_{sup}}dW= \int\limits_{\vec{\ell}_{1}}^{\vec{\ell}_{2}} \vec{ F} \cdot d\vec{\ell}$$ it is ...
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1answer
60 views

Difference between Higgs mechanism and Higgs decay

What is the difference between Higgs Mechanism and Higgs decay? I know that Higgs mechanism is a process which provide the mass to gauge boson. In general, many literature explain Higgs mechanism ...
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2answers
138 views

Definition of torque for a continuous body

I am working on basic physics definitions. Given a particle at position $r$ (in some coorinate reference system) upon which acts a force $F$, the $torque$ $\tau$ is defined by \begin{equation} ...
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2answers
156 views

What is a conservative force?

Currently I have three different pictures to describe/understand conservative forces. For the moment I just want to get an electron from point A to point B. In the near surrounding is another electron ...
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1answer
316 views

Modular invariance of CFT

I am looking at the Cardy formula for entropy in CFT, and in the article 'Kerr/CFT correspondence and its Extensions' there is a sentence: In any unitary and modular invariant CFT, the asymptotic ...
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1answer
3k views

Does a force do work on an object with constant velocity?

I know that a force does no work on an object if the object's displacement is zero, but if an object is moving at a constant velocity $\bar{v}$, and a force $\bar f$ (let's say that $\bar f$ and $\bar ...
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1answer
315 views

What would it take for a physical phenomenon to be telekinetic?

I've just watched an episode by MinutePhysics called "Real World Telekinesis". In it, Neil Turok (I wonder if that is his actual name; I remember playing a game called "Turok: Dinosaur Hunter" on ...
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1answer
244 views

Why the kilogram is not defined? [duplicate]

Possible Duplicate: Why do we still not have an exact definition for a kilogram? I was thinking about SI units. I found the following definition for the base units: Meter: distance ...
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1answer
699 views

Wave packets v.s. wave trains

Could someone please explain the difference between a wave packet and a wave train? I have rummaged around online but have not been able to find a definitive definition.