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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5
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4answers
160 views

Definition of Entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
3
votes
2answers
80 views

Line integral definition of work clarification

So I am kind of confused about the role of force when calculating work. Specifically, when defining work using a line integral. There is a paragraph in my calculus book that is really throwing me off ...
4
votes
1answer
313 views

Hamiltonians, density of state, BECs

When working with Bose-Einstein condensates trapped in potentials, how can one tell what the density of state of a system of identical bosons given the Hamiltonian, $H$? (I have been told that it is ...
2
votes
1answer
1k 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 ...
1
vote
1answer
76 views

What is kinetic energy?

Kinetic energy of an object is the energy hat it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained ...
1
vote
1answer
26 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?
0
votes
1answer
37 views

Mathematical misunderstanding of Work-Potential Energy Theorem?

This is a relatively basic question, but I don't understand why it is the case. This is from my dynamics book and is mainly a mathematical misunderstanding. $$ \ dU = F\cos\theta ds $$ Which means ...
0
votes
1answer
52 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 ...
0
votes
1answer
51 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
0
votes
1answer
32 views

What does it mean by coherence between waves?

I know by definition, coherence is pair of waves that have constant phase difference. What does this mean? Does it mean they are always have a 360 degrees, or 0 degrees phase difference? Or could they ...
3
votes
0answers
30 views

Is renormalization associated with a volume scale or with an energy-momentum and length scale?

Given that real-space renormalization blocks together small volume elements to construct larger volume elements, is it more appropriate/helpful to consider the renormalization scale to be a volume ...
2
votes
0answers
77 views

What are Killing spinors?

What are Killing spinors? How can they be motivated? Are they directly related to Killing vectors and Killing tensors and is there an overarching motivation for all three objects? Any answer is ...
2
votes
0answers
42 views

Regular initial data

I have a very basic question. What exactly is meant by "regular" initial data in general relativity? Does it mean smooth? at least $C^{2}$? All literature on the subject just uses this term without ...
2
votes
0answers
118 views

Holonomy twisting

There is Witten's topological twist of standard SUSY QFTs with enough SUSY into Witten-type TQFTs. What is a holonomy twist?
1
vote
0answers
58 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 $k=\frac{n}{N}\frac{2\pi}{a}=\frac{n}{N}$, ...
1
vote
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 ...
1
vote
0answers
388 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?
0
votes
0answers
12 views

Direction, closeness and range of streamlines in a flow domain with solid boundary and free surface?

I have a flow-field with solid boundaries and a free surface, I have plotted the streamlines, however I am not sure whether my graph is correct. In fact, I drew the streamlines by taking a range of ...
0
votes
0answers
30 views

The relationship between the two statistical mechanical definitions of entropy

It seems like similar questions have been asked here; hopefully my question is not a duplicate. I am reading my textbook on the statistical mechanical definitions of entropy, and I am very confused ...
0
votes
0answers
54 views

Equilibrium Condition

In classical thermodynamics, equilibrium conditions means maximum entropy for a closed state. However, people always talk about equilibrium for open systems as well. How can one say that an open ...
0
votes
0answers
84 views

Streamlines tangent to velocity vector

As from the title, I'm not too sure how they are related. Definition is that streamlines are instantaneously tangential to the velocity vector of the field. Why would a streamline that shows direction ...