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37
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9 answers
How can a simple physical situation give rise to two different possible outcomes?
An object of mass $5\, \mathrm{kg}$ is projected with a velocity $20\, \mathrm{ms}^{-1}$ at an angle $60^{\circ}$, to the horizontal. At the highest point of its path, the projectile explodes and breaks up into two fragments of masses $1\,…
Tanisha Daharwal
- 487
37
votes
3 answers
Why does the metric system use "kilogram" as a base SI unit?
SI system uses all (that I know) measurement basic units as 1 (single) instance: meter, second, Ampère, etc, except for the KILOgram. It already defined with 1000 multiplier (kilo).
It prevents from using usual multiplier prefixes: mega, giga, tera,…
Sasha
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37
votes
2 answers
What is the definition of a timelike and spacelike singularity?
What is the definition of a timelike and spacelike singularity?
Trying to find, but haven't yet, what the definitions are.
user23071
- 373
37
votes
4 answers
Why are the edges of a broken glass almost opaque?
Unfortunately I broke my specs today which I used in this question.
But I observed that the edges are completely different then the entire part of the lens. The middle portion of the lens was completely transparent but the edges appeared opaque (and…
Ankit
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37
votes
6 answers
Is Nm the same unit of torque as mN?
A couple of days ago, I noticed that the torque unit used by my teachers is $mN$, and while reading on the internet it came to my notice that in all textbooks the official unit is $Nm$.
I asked one teacher about it and he insisted that I'm wrong,…
37
votes
1 answer
What really are superselection sectors and what are they used for?
When reading the term superselection sector, I always wrongly thought this must have something to do with supersymmetry ... DON'T laugh at me ... ;-)
But now I have read in this answer, that for example for a free QFT highly excited states , that…
Dilaton
- 9,771
37
votes
3 answers
Why can't many models be solved exactly?
I have been told that few models in statistical mechanics can be solved exactly. In general, is this because the solutions are too difficult to obtain, or is our mathematics not sufficiently advanced and we don't know how to solve many of those…
Daphne
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37
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3 answers
What is the current status of string theory (2013)?
I've seen a bunch of articles talking about how new findings from the LHC seem to disprove (super)string theory and/or supersymmetry, or at least force physicists to reformulate them and change essential predictions.
Some examples:
Did the Large…
aditsu
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37
votes
4 answers
Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface?
The electron absorbs the energy of photon(with specific frequency)and re-emits the photon.The photon can be emitted in any direction. So why do they get re-emitted in a specific direction after reflection? On hitting normal to surface the photons…
Karan Bhatia
- 511
37
votes
8 answers
Why is it apparently not dangerous to fire a shotgun (such as when "skeet shooting") into the air?
If you fire a gun or rifle into the air, whether straight up or at an angle, as I understand physics, a metal projectile will gain surprising momentum on its way down again, more than capable of killing a grown human being, not to mention small…
user12989506
- 503
37
votes
5 answers
Why does a weather vane arrow point in the direction of the wind?
It seems that a weather vane will rotate in order to minimize energy and thus orient itself parallel to the wind.
What I do not understand is why it is implied that the weather vane arrow should point in the direction of the wind.
I do not…
user391339
- 609
37
votes
5 answers
Why is a leading digit not counted as a significant figure if it is a 1?
Reading the book Schaum's Outline of Engineering Mechanics: Statics I came across something that makes no sense to me considering the subject of significant figures:
I have searched and saw that practically the same thing is said in another book…
Vinicius ACP
- 798
37
votes
6 answers
Why doesn't the nucleus have "nucleus-probability cloud"?
While deriving the wave function why don't we take into the account of the probability density of the nucleus? My intuition says that the nucleus is also composed of subatomic particles so it will also have probability cloud like electrons have. Do…
Tim Crosby
- 1,373
37
votes
9 answers
How large would the steam explosion at Chernobyl have been?
So the second episode of the HBO series began to cover the risk of a steam explosion that led to them sending three divers into the water below the reactor to drain the tanks.
This occurred after the initial explosion that destroyed the reactor, and…
Nick S
- 475
37
votes
5 answers
How do LIGO and Virgo know that a gravitational wave has its origin in a neutron star or a black hole?
It is being said that gravitational-wave detectors are now able to distinguish neutron star waves from those originating from black holes.
Two Questions:
How do LIGO and Virgo know that a gravitational wave has its origin in a neutron star or a…
João Bosco
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