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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1answer
109 views

What is a clear definition of vibrons?

What is a clear definition of vibrons? Vibrons are localized Phonons and I need more information about them. It is somewhat vague to me. Can you give some references, please?
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2answers
68 views

What is a qualitative description of energy? [duplicate]

In elementary physics courses one is taught that energy is a measure of an object's ability to do work (this in itself seems a little flaky as how does one then define exactly what "work" is, other ...
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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 ...
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1answer
50 views

Fundamentally speaking, what are all the essential factors for waves (of any nature) to exist?

Considering all systems in which waves can exist, from atomic scale (such as DeBroglie Waves for example) to cosmic scale (gravitational waves for example), and those that require media for transport ...
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3answers
124 views

What is the difference between toy models and normal models? [closed]

Here is the short description of scientific model: an imperfect or idealized representation of a physical system And the definition of toy model: a simplified set of objects and equations ...
1
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1answer
73 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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3answers
146 views

Does the work done by a person equal the work done on the object in this situation?

If you applied a constant force over a floor that has friction on an object, would the work done by the person equal to the work done on the object? Assume that the floor is flat and that the object ...
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5answers
141 views

What is the definition of linear momentum?

Every where and book I search I get that the definition of linear momentum is the amount of speed (quantity of motion) contained in it or simply it is mass $\times$velocity? So, what is an ...
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2answers
56 views

I have trouble understanding work

I am just starting out in physics. I study in germany, so excuse me if I get some terms wrong. I am trying to understand why 'Work = Force * Way' and I think I just have some trouble imagining what ...
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0answers
27 views

What exactly is wavefield extrapolation?

I am trying to understand what exactly wavefield extrapolation is. I can understand extrapolation of a function, 'wave' and 'field' as well; but could not understand the meaning or the problem ...
2
votes
3answers
120 views

Why does Griffiths define the complex inner product differently? [closed]

I have just now noticed that Griffiths (in his book Introduction to Quantum Mechanics) defines the complex inner product as $\big<z,w\big>=\sum_{i=1}^n\overline{z}_iw_i$. In all mathematics ...
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2answers
119 views

Is this circuit a series or parallel circuit?

I saw a definition of a parallel circuit as a circuit with more than one path for current to flow. Is that the definition that's accepted? It seems like a good definition to me, but does that mean ...
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3answers
2k views

What is a mode?

Admittedly, this seems like a very simple question. The word mode pops up in every field of physics, yet I can't remember ever having read what I felt was a precise and sensible definition. After ...
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2answers
134 views

Can I define the term energy in terms of work?

Recently, I'm doing my personal task which is to formalize every definition and concept in physics, by means of formal language and of course with intuitional notes. Because I found myself that the ...
4
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2answers
430 views

Can pressure exist without a container?

I always hear pressure defined as the force exerted by particles on the walls of the container they're being held in. This makes sense since the mathematical definition of pressure is $ p = ...
0
votes
1answer
67 views

Einstein space - proper definition [closed]

Excuse, this is my first question at this forum, I try to be clear and short. What is the exact definition of Einstein spaces? It's enough to say $$ G^{\mu\nu}_{;\mu}=0~? $$ Where $$ ...
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2answers
51 views

Is the electric current a flow of charges?

Wikipedia defines charge as the fundamental property of forms of matter that exhibits electrostatic attraction or repulsion in the presence of other matter.Strictly speaking, while defining an ...
3
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1answer
129 views

What is the difference between flow and expansion?

Fluids (both liquids and gases) will move from one point in space to another due to a potential gradient. Some examples may be: 1) horizontal pipe flow, a fluid will move from a region of high ...
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3answers
105 views

Thermal diffusion and the 2nd law of thermodynamics

If we look at the definition of heat flux, $$\stackrel{\to }{J}=-\kappa\stackrel{\to }{\nabla}T \, ,$$ we may notice that it's defined to be a vector showing in the opposite direction of the ...
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1answer
234 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 ...
0
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1answer
68 views

Does the term phase difference apply only for sinusoidal waves?

This question may sound dumb, (it will to me, hopefully, in a day or two!), but does the term phase difference apply only for sinusoidal waves? Wikipedia defines 'phase' as the following: Phase ...
0
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1answer
58 views

Fermi energy on a “fermion pre-gas model”

I'm having serious trouble while trying to follow an example from Callen's "Thermodynamics and an introduction to Thermostatistics" regarding the definition of the Fermi energy. In said example one ...
6
votes
1answer
277 views

Why are the quantum observables defined on opens sets a presheaf and not a sheaf?

In local quantum field theory or AQFT one can mathematically describe over each open set $U$ of a spacetime $M$ the quantum states or observables of the theory. This structure is commonly referred as ...
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4answers
113 views

Does the definition of escape velocity apply strictly to an initial velocity of a ballistic projectile?

In Shivam Sarodia's answer to Escape Velocity question he states: "For a rocket launched exactly at escape velocity" This seems to be a repeated, and unclear way of discussing the matter of escape ...
2
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1answer
32 views

Definition of a Supercluster

A group of astronomers in September 2014 redefined what classifies a supercluster. Before this, the supercluster where the Milky Way resides was the Virgo Supercluster. Now, the Virgo Supercluster ...
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1answer
57 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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2answers
125 views

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
2
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5answers
259 views

What exactly is work?

What exactly is work? My book confuses me: a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the ...
2
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0answers
40 views

What is the definition of time? [duplicate]

I wanted to know the definition of time just like as we define displacement, current etc. **Note:**There should be no mention of time period or time interval in the definition.
1
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1answer
129 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 ...
0
votes
1answer
46 views

Beginner wondering about displacement

At the moment I am going to a physics camp. I also do vex robotics. I am trying to use the equations to help me build my robot perfectly. Right now I'm working on how fast the throwing wheels should ...
1
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1answer
67 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 ...
0
votes
1answer
55 views

How to implement the form of current density in a Hall Effect related calculation?

Please consider the following; Question. A rectangular plate of semiconducting material has dimensions 10mm x 4mm x 1mm. A current of 3 mA flows along the length and a Hall Voltage of 13.6 mV is ...
1
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1answer
179 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 ...
3
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2answers
2k views

What is a Null Geodesic? [duplicate]

What is a Null Geodesic? My textbook only explains it as the Minkowski metric which equals to zero, but I'd appreciate a more detailed explanation.
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2answers
136 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 ...
0
votes
3answers
234 views

The standard definition of current

The book says current is the rate of flow of charge per unit time, but I don't understand whether it is rate of flow of charge through a single cross-sectional area per unit time or the entire amount ...
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3answers
186 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 - ...
3
votes
1answer
72 views

What exactly is conservative vector field?

I'm studying calculus, but since the example involved a physical concept. I will ask here: This is how it goes: This means that in a conservative force field, the amount of work required to ...
0
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1answer
71 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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2answers
131 views

Why can't we precisely define physics? [closed]

While reading a textbook, I came across this statement: "A precise definition of physics is neither possible nor necessary." I was curious why it is not possible but the textbook never ...
1
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1answer
169 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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2answers
91 views

A car is moving in a circular trajectory with radius R=20m. The equation of motion is : x(t) = 15 + 8t – t^2 [closed]

We have to find the distance the car has traveled after 3s. Actually this question came up in an important exam, and the answer was: L=x(3)-x(0) But I think this is the answer for displacement, ...
0
votes
1answer
446 views

The definition of mutual capacitance

I am not sure I completely understand the definition of mutual capacitance. Let's say we have two conductors, $A$ and $B$, so that the following holds: Both conductors are isolated. $A$ is isolated ...
2
votes
2answers
379 views

What are global and local gauge invariance defined as they are?

I'm sorry for the triviality of my questions. Why is $\bar{\psi} = e^{i \theta}\bar{\psi}$, where $\theta$ is a real number, used as the global gauge transformation? Why $e^{i \theta}$; what's the ...
4
votes
2answers
177 views

Need help on electric potential definition

I'm having trouble understanding electric potential. In my book it says "an electric force acts on a charge situated in an electric field." I understand this part. Then it goes on to say "If a charge ...
1
vote
2answers
165 views

Good layman definition of the critical point(phases) and supercriticality

I've heard of this point among others, but never really got what it meant. Wikipedia makes one's head spin. The only thing I picked up is that it occurs between liquid and gas, and displays ...
6
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3answers
13k views

Inertia Vs Momentum

At my recent lesson on kinematics, my teacher taught about inertia and momentum. This is what she said. Inertia: a characteristic of an object that resists changes to its state of motion. Momentum: ...
2
votes
1answer
63 views

How can I physically demonstrate potential difference in a circuit to a 14 year old?

Children of this age have a fair idea about current, resistance, and batteries. Potential difference is a thing that cannot be felt or physically visualized. A teenager asked me if he can touch ...
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6answers
957 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.