The notation tag has no wiki summary.
0
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3answers
164 views
Why is 'the period' marked as letter T?
I'm not a native English speaker and I was wondering, why 'the period' got the letter $T$.
I've asked myself the question when I was thinking about stuff related to the frequency. I.e.:
$f$ - ...
0
votes
1answer
262 views
Relationship between acceleration, velocity and position
I'm learning some applications for equation of motion. But I'm failing to relate velocity, acceleration and position.
If $v=\frac{dr}{dt}$ and $a=\frac{dv}{dt}$, why $a$ is $\frac{d^2r}{dt^2}$ ...
2
votes
3answers
240 views
How to distinguish 4D and 3D vectors in handwriting?
Usually vectors are denoted with bold font in printbooks and with arrows above in handwriting.
In Thorn's e al. Gravitation, 4D vectors are denoted with bold and 3D vectors with bold italic. How to ...
0
votes
3answers
261 views
Differential squared vs. differential of squared
Why it is said that
$$\frac{dx^2}{dt^2}=\upsilon^2$$
I can only understand the following one:
$$\left (\frac{dx}{dt} \right)^2=\upsilon^2$$
Edit:
Excerpt from Landau's Mechanics:
Execrpt from ...
0
votes
2answers
138 views
When to use $f$ and when $\nu$ signifying frequency?
When to use $f$ and when $\nu$ signifying frequency? I guess that when you mean frequency of electromagnetic wave, you use $\nu$, and $f$ otherwise?
4
votes
1answer
276 views
Why is $L^2$ norm of the gradient called kinetic energy?
I'm reading Lieb-Loss's book 'Analysis', chapter 7. The authors refer to the following integral:
$$\tag{1} \lVert \nabla f\rVert_2^2=\int_{\Omega}\lvert \nabla f(x)\rvert^2\, d^nx $$
as the kinetic ...
1
vote
2answers
250 views
Question with Einstein notation
Let’s consider this equation for a scalar quantity $f$ as a function of a 3D vector $a$ as:
$$ f(\vec a) = S_{ijkk} a_i a_j $$
where $S$ is a tensor of rank 4. Now, I’m not sure what to make of the ...
4
votes
1answer
76 views
$\pm$ (light-cone?) notation in supersymmetry
I would like to know what is exactly meant when one writes $\theta^{\pm}, \bar{\theta}^\pm, Q_{\pm},\bar{Q}_{\pm},D_{\pm},\bar{D}_{\pm}$.
{..I typically encounter this notation in literature on ...
1
vote
1answer
155 views
Rocket drive and conservation of momentum
I am currently reading through some lecture notes of Physics 1 and in a chapter about the dynamics of the mass point, there is an example covering the rocket drive.
Let $v$ be the velocity of the ...
2
votes
2answers
62 views
Another question about Shankar's notation
I have another question on the notation in Shankar. I think it's sloppy, but I also may just be misunderstanding it. Again, this is at the very beginning of the math intro.
He has:
$$a\left| V ...
1
vote
2answers
209 views
Question on notation in Shankar's Quantum Mechanics - math intro on vector spaces
I'm just beginning Shankar's 2nd edition Quantum Mechanics and having some trouble with notation. He defines his vectors as "$\left|V\right>$" . And with a scalar multiplier as "$a\left|V\right>$" . ...
3
votes
4answers
127 views
Is there a recognised standard for typesetting quantum mechanical operators?
Firstly, I wasn't sure exactly where to put this. It's a typesetting query but the scope is greater than $\TeX$; however it's specific also to physics and even more specific to this site.
I've ...
1
vote
2answers
160 views
Why no basis vector in Newtonian gravitational vector field?
In my textbook, the gravitational field is given by$$\mathbf{g}\left(\mathbf{r}\right)=-G\frac{M}{\left|\mathbf{r}\right|^{2}}e_{r}$$
which is a vector field. On the same page, it is also given as a ...
15
votes
1answer
1k views
Differentiating Propagator, Greens function, Correlation function, etc
For the following quantities respectively, could someone write down the common definitions, their meaning, the field of study in which one would typically find these under their actual name, and most ...
13
votes
4answers
2k views
What does Peter Parkers formula represent?
Okay, so the trailer for the new Spider Man movie is out and appearently our friendly physicist from the neightborhood came up with something. However I can't find out what this is.
...
3
votes
2answers
376 views
Bra-ket notation and linear operators
Let $H$ be a hilbert space and let $\hat{A}$ be a linear operator on $H$.
My textbook states that $|\hat{A} \psi\rangle = \hat{A} |\psi\rangle$. My understanding of bra-kets is that $|\psi\rangle$ is ...
1
vote
1answer
741 views
What does $\Psi^*$ mean in Schrodinger's Equation?
I am not a physics student. In one of my courses, some fundamental concepts of Quantum mech were needed, so i was gng through them when i stumbled upon this
It says
$$\text{probability} = ...
2
votes
2answers
309 views
Correct application of Laplacian Operator
Not a physicist, and I'm having trouble understanding how to apply the Laplacian-like operator described in this paper and the original. We let:
$$ \hat{f}(x) = f(x) + \frac{\int H(x,y)\psi(y) ...
5
votes
3answers
63 views
which letter to use for a CFT?
In math, one says "let $G$ be a group", "let $A$ be an algebra", ...
For groups, the typical letters are $G$, $H$, $K$, ...
For algebras, the typical letters are $A$, $B$, ...
I want to say ...
1
vote
2answers
192 views
Subshell notation for hydrogen cation?
Looking at $s$,$p$,$d$ configuration for atoms & ions: Since a hydrogen cation $H^+$ has no electron, how would the subshell notation be written? My best estimate would be $1s^0$.
0
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2answers
189 views
How is an arbitrary operator usually denoted in quantum mechanics?
Which symbols are usually used to denote an arbitrary operator in quantum mechanics, such as O in the following example?
$O \mbox{ is Hermitian} \Leftrightarrow \Im{\left< O \right>} = 0$
1
vote
1answer
284 views
state vector notation
I've never taken a quantum mechanics class, but I find myself now using principles developed in the quantum theory of angular momentum. One particularly confusing aspect that I'm struggling with is ...
1
vote
2answers
227 views
Notation of plane waves
Consider a monochromatic plane wave (I am using bold to represent vectors)
$$ \mathbf{E}(\mathbf{r},t) = \mathbf{E}_0(\mathbf{r})e^{i(\mathbf{k} \cdot \mathbf{r} - \omega t)}, $$
$$ ...
