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1500 questions
36
votes
6 answers
Blowing your own sail?
How it this possible? Even if the gif is fake, the Mythbusters did it and with a large sail it really moves forward. What is the explanation?
mathematiccian
- 469
36
votes
5 answers
Is there a physical system whose phase space is the torus?
NOTE. This is not a question about mathematics and in particular it's not a question about whether one can endow the torus with a symplectic structure.
In an answer to the question
What kind of manifold can be the phase space of a Hamiltonian…
joshphysics
- 57,120
36
votes
5 answers
Why can't we feel the Earth turning?
The Earth turns with a very high velocity, around its own axis and around the Sun.
So why can't we feel that it's turning, but we can still feel earthquake.
lamwaiman1988
- 509
36
votes
7 answers
Why can't you hear music well over a telephone line?
Why can't you hear music well well over a telephone line?
I was asked this question in an interview for a university study placement and I unfortunately had no idea.
I was given the hint that the telephone sampling rate is 8000 samples per second.
Danny Rancher
- 499
36
votes
3 answers
Best Sets of Physics Lecture Notes and Articles
This post is inspired by this math.se post.
Let me start by apologizing if there is another thread on phys.se that subsumes this.
I often find that I learn best from sets of lecture notes and short articles. There are three particular reasons that…
Hakim
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35
votes
4 answers
Are atoms unique?
Do atoms have any uniquely identifying characteristic besides their history?
For example, if we had detailed information about a specific carbon atom from one of Planck's fingerprints, and could time-travel to the cosmic event in which the atom…
Charles Burns
- 423
35
votes
1 answer
How to define orbital angular momentum in other than three dimensions?
In classical mechanics with 3 space dimensions the orbital angular momentum is defined as
$$\mathbf{L} = \mathbf{r} \times \mathbf{p}.$$
In relativistic mechanics we have the 4-vectors $x^{\mu}$ and $p^{\mu}$, but the cross product in only defined…
asmaier
- 9,794
35
votes
3 answers
Eigenfunctions of the Runge-Lenz vector
The hamiltonian for the hydrogen atom,
$$
H = \frac{\mathbf{p}^2}{2m} - \frac{k}{r}
$$
is spherically symmetric and it therefore commutes with the angular momentum $\mathbf{L}$; this causes all its eigenfunctions with equal angular momentum number…
Emilio Pisanty
- 132,859
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- 666
35
votes
9 answers
Is coherent light required for interference in Young's double slit experiment?
In this Veritasium video, a home experiment is presented which appears to produce a very good double-slit interference pattern with normal sunlight.
The experiment is an empty cardboard box with a visor and a placeholder for a microscope slide with…
AnimatedPhysics
- 628
35
votes
1 answer
Is general relativity holonomic?
Is it meaningful to ask whether general relativity is holonomic or nonholonomic, and if so, which is it? If not, then does the question become meaningful if, rather than the full dynamics of the spacetime itself, we consider only the dynamics of…
user4552
35
votes
4 answers
Gravity as a gauge theory
Currently, (classical) gravity (General Relativity) is NOT a gauge theory (at least in the sense of a Yang-Mills theory).
Why should "classical" gravity be some (non-trivial or "special" or extended) gauge theory? Should quantum gravity be a gauge…
riemannium
- 6,491
35
votes
7 answers
Why do people still talk about bohmian mechanics/hidden variables
I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal variables as yet unknown which determine its…
yayu
- 4,822
35
votes
3 answers
If aerographite is lighter than air, why doesn't it float?
Air is 6 times denser than aerographite but looking at pictures or videos presenting the material, I see it resting on tables rather than raising to the ceiling.
Also, since the material is made of carbon nanotubes, I assume there are empty spaces…
Youcha
- 455
35
votes
12 answers
Is it correct to say that it is theoretically impossible for perfect rigid bodies to exist?
If perfect rigid bodies were to exist, then consider a scenario in which two rigid bodies of equal masses moving with velocities of equal magnitude but opposite in direction colliding against one another. During the collision, the velocities of both…
Mathew_
- 538
35
votes
4 answers
How can earthquakes shift the earth's axis?
One often comes across news articles that claim that an earthquake shifted the earth's axis.
http://news.google.com/?q=earthquake%20shifted%20OR%20shifts%20earth%27s%20axis
If you ignore the influence of other celestial bodies, an internal event…
dbrane
- 8,770