Use this for questions relating to the proper use of physics terminology or nomenclature.
Questions tagged [terminology]
2310 questions
96
votes
9 answers
Are matrices and second rank tensors the same thing?
Tensors are mathematical objects that are needed in physics to define certain quantities. I have a couple of questions regarding them that need to be clarified:
Are matrices and second rank tensors the same thing?
If the answer to 1 is yes, then…
Revo
- 17,504
94
votes
15 answers
What is the difference between "kinematics" and "dynamics"?
I have noticed that authors in the literature sometimes divide characteristics of some phenomenon into "kinematics" and "dynamics".
I first encountered this in Jackson's E&M book, where, in section 7.3 of the third edition, he writes, on the…
nibot
- 9,691
78
votes
7 answers
Is Pauli-repulsion a "force" that is completely separate from the 4 fundamental forces?
You can have two electrons that experience each other's force by the exchange of photons (i.e. the electromagnetic force). Yet if you compress them really strongly, the electromagnetic interaction will no longer be the main force pushing them apart…
Jan M.
- 1,162
77
votes
20 answers
Is weight a scalar or a vector?
My professor insists that weight is a scalar. I sent him an email explaining why it's a vector, I even sent him a source from NASA clearly labeling weight as a vector. Every other source also identifies weight as a vector.
I said that weight is a…
Ryan
- 787
69
votes
5 answers
What does Enthalpy mean?
What is meant by enthalpy? My professor tells me "heat content". That literally makes no sense. Heat content, to me, means internal energy. But clearly, that is not what enthalpy is, considering: $H=U+PV$ (and either way, they would not have had two…
PhyEnthusiast
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- 3
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60
votes
7 answers
What is the connection between special and general relativity?
What is the connection between special and general relativity? As I understand general relativity does not need the assumption on speed of light constant.
It is about the relation between mass and spacetime and gravity.
Can general relativity be…
Sharon Salmon
- 719
45
votes
3 answers
What is a mode?
The word mode pops up in many fields of physics, yet I can't remember ever encountering a simple but precise definition.
After having searched fruitlessly on this site as well, an easy to find place with (one or more) good answers seems in…
Janosh
- 1,294
43
votes
3 answers
What is meant by the term "completeness relation"
From my humble (physicist) mathematics training, I have a vague notion of what a Hilbert space actually is mathematically, i.e. an inner product space that is complete, with completeness in this sense heuristically meaning that all possible…
user35305
- 3,327
43
votes
5 answers
Hilbert space vs. Projective Hilbert space
Hilbert space and rays:
In a very general sense, we say that quantum states of a quantum mechanical system correspond to rays in the Hilbert space $\mathcal{H}$, such that for any $c∈ℂ$ the state $\psi$ and $c\psi$ map to the same ray and hence are…
user929304
- 4,910
42
votes
6 answers
Difference between theoretical physics and mathematical physics?
I'm a huge fan of mathematical physics and I know what the formal definitions of those two areas are, I've seen them. But I still get completely baffled when someone asks me to explain it simply. The difference is obvious to me, but I just can't…
user20250
41
votes
12 answers
What does it mean when people say "Physics break down"?
So I keep hearing people talking about how physics break down at for example the center of a black hole. And maybe I am just to stupid but, why? How can we say that? For all we know a black hole could just be a very dense sphere. Kind of like a…
Erik Hall
- 619
39
votes
2 answers
Definitions: 'locality' vs 'causality'
I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different things to the author.
My current understanding…
user1247
- 7,509
38
votes
8 answers
Gibbs free energy intuition
What is Gibbs free energy? As my book explains:
Gibbs energy is the energy of a system available for work.
So, what does it want to tell? Why is it free? Energy means ability to do work. What is so special about this energy? Can anyone simply…
user36790
37
votes
8 answers
Is the Big Bang defined as before or after Inflation?
Is the Big Bang defined as before or after Inflation? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've been doing some reading while writing up my thesis…
Jim
- 24,676
36
votes
10 answers
Why are only infrared rays classified as "heat rays"?
I've often heard that Infrared rays are called "heat rays". However, I feel like this term is a misnomer. Don't all the wavelengths of electromagnetic radiation carry energy?
Judging by how gamma rays are highly penetrating and are dangerous when…
Cross
- 3,360