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1500 questions
53
votes
1 answer
What is the relationship between different types of quantum field theories?
As far as I know, all known quantum field theories have the same very broad structure: one gives some finite list of data in order to specify a particular QFT, then one uses some formalism to algorithmically extract various physical observables from…
tparker
- 47,418
53
votes
12 answers
Is there an intuitive explanation for why Lorentz force is perpendicular to a particle's velocity and the magnetic field?
The Lorentz force on a charged particle is perpendicular to the particle's velocity and the magnetic field it's moving through. This is obvious from the equation:
$$ \mathbf{F} = q\mathbf{v} \times \mathbf{B} $$
Is there an intuitive explanation for…
Stephen Jennings
- 639
53
votes
3 answers
Why is ice made from boiled water clear?
A common trick to make clear water ice is to boil pure water prior to freezing it. Why does that work and what are the white inclusions in ice that was made from unboiled tap water?
DK2AX
- 4,779
53
votes
2 answers
Why does sound absorption in oceans depend on the pH?
I was reading "The Sixth Extinction: An Unnatural History", by Elizabeth Kolbert, and there she comments that high level of $CO_{2}$ in the atmosphere lowers the pH of oceans (which makes sense) and, consequently, diminishes sound absorption:
WHY…
Gabriel Cozzella
- 1,193
53
votes
5 answers
What did general relativity clarify about Mercury?
I frequently hear that Kepler, using his equations of orbital motion, could predict the orbits of all the planets to a high degree of accuracy -- except Mercury. I've heard that mercury's motion couldn't be properly predicted until general…
Carson Myers
- 5,041
53
votes
6 answers
In electrostatics, why the electric field inside a conductor is zero?
In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.
I have 2 questions:
We know that conductors…
Revo
- 16,956
53
votes
1 answer
How does this "simple" electric train work?
In this YouTube video, a dry cell battery, a wound copper wire and a few magnets (see image below) are being used to create what can be described as "train". It looks fascinating but how does this experiment work?
Update 8th August 2016: This…
noir1993
- 2,106
53
votes
3 answers
How is the Saddle point approximation used in physics?
I am trying to understand the saddle point approximation and apply it to a problem I have but the treatments I have seen online are all very mathematical and are not giving me a good qualitative description of the method and why it's used and for…
BeauGeste
- 1,581
53
votes
5 answers
Good reading on the Keldysh formalism
I'd like some suggestions for good reading materials on the Keldysh formalism in the condensed matter physics community. I'm familiar with the imaginary time, coherent state, and path integral formalisms, but lately, I've been seeing Keldysh more…
user129
- 457
53
votes
49 answers
Common false beliefs in Physics
Well, in Mathematics there are somethings, which appear true but they aren't true. Naive students often get fooled by these results.
Let me consider a very simple example. As a child one learns this formula $$(a+b)^{2} =a^{2}+ 2 \cdot a \cdot b +…
C.S.
- 1,029
52
votes
4 answers
What's the difference between the five masses: inertial mass, gravitational mass, rest mass, invariant mass and relativistic mass?
I have learned in my physics classes about five different types of masses and I am confused about the differences between them.
What's the difference between the five masses:
inertial mass,
gravitational mass,
rest mass,
invariant…
QEntanglement
- 3,831
52
votes
0 answers
Can Lee-Yang zeros theorem account for triple point phase transition?
Now the prominent Lee-Yang theorem (or Physical Review 87, 410, 1952) has almost become a standard ingredient of any comprehensive statistical mechanics textbook.
If the volume tends to infinity, some complex roots of the grand canonical partition…
xiaohuamao
- 3,621
52
votes
7 answers
Solving the helicopter hanging cable problem through differential analysis
The above problem is taken from the 2014 $F=ma$ contest.
This question generated a great deal of controversy. At least two test takers challenged the
answer, one who even tried to do the experiment. I’m told that several different…
Neox
- 645
52
votes
17 answers
Quantum mechanics and everyday nature
Is there a phenomenon visible to the naked eye that requires quantum mechanics to be satisfactorily explained? I am looking for a sort of quantic Newtonian apple.
user1975053
- 663
52
votes
2 answers
How small can a flame get?
Last time I was watching a candle die. After its wick was finished, there remained just a drop of molten wax that was still slowly burning, with a flame that became smaller and smaller, down to a millimeter high, until it disappeared.
It made me…
Anthony Guillen
- 1,801