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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53 views

What is “forward peaking”?

In "Research and Development for a Gadolinium Doped Water Cherenkov Detector" the phrase "forward peaking" is used to describe a signal. This comes up in lots of other contexts too, but I still can't ...
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3answers
614 views

Definition of a normal mode?

What is the formal definition of a normal mode for a string? And how does this relate to the definition from e.g. wiki that seem to be applied to discrete systmes of particles only? Also on a string ...
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410 views

Extensive variables in thermodynamics

Extensive variables in thermodynamics are those which scale linearly with the system size. It is known that a ratio of two extensive variables is an intensive variable. Now, the number of particles ...
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1answer
105 views

How can we define the energy stored in a (conservative) force field?

I have come to know from my textbook that energy is stored in the E-field of a capacitor, in the B-field of an inductor and so on. Take the example of an inductor. The derivation bewilders me ...
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13k 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
202 views

What is the difference between a skew-symmetric and an antisymmetric tensor?

What is the difference between a skew-symmetric and an anti-symmetric tensor? If they represent the same tensor, then why use different labeling.
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2answers
372 views

Is there a definition of force? [duplicate]

Well, Newton's three laws talks about forces, but no definition is given. In truth, Newton's second law gives an idea of what total force is: the time change rate of momentum. But, if we have a force ...
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107 views

What is a geometrical object?

From the Wikipedia link for Geometry: Geometry (Ancient Greek: γεωμετρία; geo- "earth", -metron "measurement") is a branch of mathematics concerned with questions of shape, size, relative position ...
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1answer
802 views

Difference between Poynting vector and energy flux density?

Are those two terms the same, or...? My book says that the Poynting vector is an energy flux density given by: $$\mathbf{S} = \frac{1}{\mu_{0}}(\mathbf{E} \times \mathbf{B})$$ So that alone should ...
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1answer
293 views

How do you actually define an orbit?

How do you actually define an orbit? I believe, Newtonian Mechanics describes an orbit as one object in free fall around another where projectile paths become elliptical. I think, Einstein describes ...
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2answers
1k views

Why is work defined as force dot displacement?

Why is work defined as force dot displacement? I know that it is defined like that based on the observational fact - we do more work when we apply greater force or move to a greater distance. But I ...
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1answer
373 views

Relative Change of Volume

Simple question, in materials publications I often see the relative change of volume in a system reported as $$ \Delta \left (V \right )/V $$ is the denominator volume supposed to be initial or the ...
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3answers
150 views

Gravitational acceleration

'What is difference between free fall acceleration g and gravitational acceleration a?***a is with subscript g.In my textbook it is written that "free fall acceleration = gravitational acceleration - ...
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2answers
117 views

How this formula for work follows from the definition?

If a particle moves along a path $\gamma : I\subset \mathbb{R}\to \mathbb{R}^3$ then the work done by a force $\mathbf{F}$ is defined by $$W = \int_{\gamma} \mathbf{F} = ...
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1answer
845 views

What's the difference between microscopy and spectroscopy?

Both methods collect particles or electromagnetic waves, and in both methods it's possible to reconstruct a 2D image, which may represent morphology (AFM, LEED for example), electronic structure (STM, ...
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135 views

Mathematical Definition of Locality

What is the mathematically precise definition of principle of locality in physics for a continuous space-time in the sense that an object is only directly influenced by its immediate surroundings?
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1answer
5k 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
4k views

Definition of “intensive” and “extensive” properties

Today I was asked what does it mean for a physical property of a system to be intensive. My first answer, loosely speaking, was: "It is a property that is local." I was specifically thinking ...
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1answer
136 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
250 views

Definition of energy

What is the definition of energy $E$ given a dispersion relation $\omega=\omega(k)$ where $k=|\vec k|$ and $\omega$ is not necessarily linearly proportional to $k$? What about momentum $\vec p$? This ...
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2k views

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
192 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
1k views

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
33 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 ...
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1answer
46 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
81 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
113 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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128 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
100 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
548 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
164 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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184 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
82 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
59 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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76 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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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
112 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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361 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
193 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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43 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
58 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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107 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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864 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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79 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
90 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
190 views

What is many-body bound state?

Bound state by definition is a state when particles are bounded together, so then "many-body bound state" would be bound state for a system of many bodies. Then I have several puzzles: 1. is the state ...
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65 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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3answers
491 views

What exactly is the “coherence” between waves?

I know, by definition, that coherence means that a pair of waves have constant phase difference. What does this mean? Does it mean they always have a 360 degrees, or 0 degrees phase difference? Or ...
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1answer
195 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 ...