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.
2
votes
1answer
104 views
Doubts about the definition of mass
I'm having some problems understanding what are the possible definitons of mass and how they are related to each other.
In Classical Mechanics, we can distinguish between inertial and gravitational ...
2
votes
3answers
123 views
What is the general statistical definition of temperature?
Temperature in an isolated system is defined as:
$$\frac{1}{T} = -\frac{\partial{S(E,V,N)}}{\partial{E}} $$
But I wonder how one can generalize this to a random system.
Or for instance to a point in ...
0
votes
1answer
26 views
Viewing a reference frame from inside of it?
Can one observe one's own frame of reference without moving out side the frame?
For example, if you are on a train and you throw ball in the air up and down.
When you are on the train (frame 1) you ...
3
votes
4answers
116 views
What do people actually mean by “rolling without slipping”?
I have never understood what's the meaning of the sentence "rolling without slipping". Let me explain.
I'll give an example. Yesterday my mechanics professor introduced some concepts of rotational ...
0
votes
3answers
2k 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 ...
3
votes
0answers
96 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?
10
votes
1answer
368 views
What accounts for the discrepancies in my calculations of year lengths?
A common exercise in many introductory astronomy texts is to use the lengths of various kinds days to calculate the approximate length of the corresponding year.
For example, ratio $k$ of the length ...
0
votes
2answers
50 views
Definition of Static Electricity
The result of an imbalance of electrons between objects is called static electricity. It is called "static" because the displaced electrons tend to remain stationary after being moved from one ...
0
votes
2answers
76 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 ...
1
vote
2answers
53 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 ...
3
votes
4answers
1k views
What is the difference between center of mass and center of gravity?
What is the difference between center of mass and center of gravity?
These terms seem to be used interchangeably.
Is there a difference between them for non-moving object on Earth, or moving objects ...
1
vote
0answers
65 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 ...
2
votes
1answer
78 views
Question on Radiance equation
The radiance equation is
$$
L = \frac{d}{dA} \frac{2(\phi)}{dW cos(\theta)} (watt/srm^2)
$$
where $\phi$ is the flux.
I am thinking, should not be the cosine term on the numerator instead of the ...
0
votes
1answer
151 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 ...
0
votes
6answers
1k views
What distinguishes between physics and chemistry? [closed]
What are the major differences between physics and chemistry? I know that they both study atoms, electrons and molecules, but what makes some topics part of one and some part of another?
2
votes
1answer
49 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 ...
0
votes
1answer
55 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 ...
1
vote
2answers
52 views
Electrostatic Potential Definition
In the book, Introduction to electrodynamics by David J. Griffiths, he introduces potential separately as a function and potential energy through that function.
How can potential be defined before ...
9
votes
4answers
225 views
Two planets in same orbit - not planets?
Let us pretend for a moment that there are two identical planets that are exactly opposite their star from each other and are the same distance from said star. (This would make them, at all times, ...
10
votes
5answers
2k views
What is an asterism compared to a constellation?
I'm doing an astronomy exam tomorrow and in the practice paper it asks for the difference between constellation and asterism. It seems asterism is a group of recognizable stars; however I thought that ...
3
votes
1answer
78 views
For how long must a molecule remain stable to be considered “stable”?
In the Star Trek: Voyager episode The Omega Directive, Seven of Nine says that the Borg synthesized a molecule which was "kept [] stable for one trillionth of a nanosecond before it destabilized". ...
1
vote
1answer
53 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 ...
2
votes
2answers
3k views
What is the exact definition of center of gravity?
I've come across many definitions. Is it
1) The point from which the weight of the body acts, i.e., the point at which if the entire mass of the body is assumed to be concentrated, the gravitational ...
1
vote
1answer
83 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 ...
2
votes
2answers
3k views
Are all metals good conductor of electricity?
I am writing an article for kids, which is on conductors and insulators of electricity.
If I make a statement that "All metals are electrical conductors and all non-metals are electrical insulators" ...
1
vote
3answers
284 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 ...
0
votes
0answers
59 views
Curvilinear abscissa confusion
How's exactly defined the curvilinear abscissa in kinematics? Surfing on the net I found different definitions:
a) Fixed a point $O$ and a direction, the curvilinear abscissa $s$ at a point $P$ is ...
0
votes
0answers
193 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?
4
votes
3answers
478 views
Why is 1 AU the distance between the Sun and the Earth?
Why 1 AU is defined as the distance between the Sun and the Earth? (approximately if you like to be precise)
An astronomical unit (abbreviated as AU, au, a.u., or ua) is a unit of length ...
3
votes
1answer
50 views
Does a reference or classification standard for altitude classifications of geocentric orbits exist?
I'm looking for a primary reference of the altitude classifications of geocentric orbits (LEO, MEO, GEO, HEO), but I was not able to find something so far.
I noticed that there is very different ...
5
votes
1answer
6k views
Is the moon a planet?
Can our moon qualify as a planet? With regard or without regard to the exact definition of the planet, can the moon be considered as planet as Mercury, Venus and Earth etc. not as the satellite of the ...
7
votes
6answers
860 views
What is a tensor?
I have a pretty good knowledge of physics but couldn't understand what a tensor is. I just couldn't understand it, and the wiki page is very hard to understand as well. Can someone refer me to a good ...
4
votes
1answer
98 views
Does the Kelvin have a rigorous definition?
From Wikipedia:
The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water.
That presupposes that we can take a fraction of temperature.
Now, ...
0
votes
0answers
18 views
Rice Allnatt distribution function
Can anyone give me an article of which explains Rice Allnatt distribution function or can you explain the function here?
4
votes
1answer
45 views
Vesta dwarf planet status
Now that we have close-up photos of Vesta, which the IAU had previously said was a candidate dwarf planet, when is the IAU going to decide the issue? Personally, Vesta doesn't look round enough to me.
...
7
votes
4answers
3k views
What is sound and how is it produced?
I've been using the term "sound" all my life, but I really have no clue as to what sound exactly is or how it is created. What is sound? How is it produced? Can it be measured?
2
votes
1answer
83 views
What examples are there of fuzzy concepts in astronomy?
What examples are there of fuzzy concepts in astronomy? In particular, how fuzzy are the boundaries between different types of stars?
As an example of a fuzzy concept I'm thinking of the planet/brown ...
13
votes
7answers
1k views
What is a general definition of impedance?
Impedance is a concept that shows up in any area of physics concerning waves. In transmission lines, impedance is the ratio of voltage to current. In optics, index of refraction plays a role similar ...
3
votes
1answer
222 views
What is “charge discreteness”?
I assume it is some kind of quantity. Google only made things more confusing.
I get that it has something to do with circuits.
I also get what a discrete charge is. In fact, I thought charges ...
0
votes
2answers
94 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 ...
2
votes
3answers
65 views
Name for celestial “Prime Meridian”?
Is there name for the line that goes from celestial pole to pole at RA 0 degrees 0 minutes 0 seconds? On Earth we would call it the Prime Meridian. Is it called the "Celestial Meridian"?
3
votes
0answers
20 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 ...
7
votes
2answers
63 views
What distinguishes a moon from orbiting space debris? Or in other words, when is a satellite “too small” to be a moon?
The Wikipedia article on Natural Satellites doesn't really give an adequate distinction as to what distinguishes a moon from other orbiting bodies. What I am looking for is a classification that ...
7
votes
7answers
5k views
Simple explanation of quantum mechanics
Can you please describe quantum mechanics in simple words? When ever I read this word (quantum computers, quantum mechanics, quantum physics, quantum gravity etc) I feel like fantasy, myth and ...
3
votes
2answers
165 views
Definition of “Quantizing”
Could anyone explain to me what "quantize" means in the following context?
Quantize the 1-D harmonic oscillator for which
$$H~=~{p^2\over 2m}+{1\over 2} m\omega^2 x^2.$$
I understand that the ...
6
votes
1answer
170 views
Operator Ordering Ambiguities
I have been told that $$[\hat x^2,\hat p^2]=2i\hbar (\hat x\hat p+\hat p\hat x)$$ illustrates operator ordering ambiguity.
What does that mean?
I tried googling but to no avail.
8
votes
2answers
923 views
273 + degree Celsius = Kelvin. Why 273?
Temperature conversion:
273 + degree Celsius = Kelvin
Actually why is that 273? How does one come up with this?
My teacher mentioned Gann's law (not sure if this is the one) but I couldn't find ...
15
votes
1answer
1k views
Differentiating Propagator, Greens function, Correlation function, etc
For the following quantities respectively, could someone write down the common definitions, their meaning, the field of study in which one would typically find these under their actual name, and most ...
6
votes
1answer
180 views
Introduction to Gauge Symmetries: Good, Bad or Ugly?
I'm trying to come up with a good (as in intuitive and not 'too wrong') definition of a gauge symmetry.
This is what I have right now:
A dynamical symmetry is a (differentiable) group of ...
-1
votes
1answer
105 views
Poles, wavefunctions, transmission
Why is it said that $\operatorname{sech}x$ (a transmission amplitude) has a simple pole on the imaginary axis? Thanks.
