0
votes
0answers
9 views
In which position does the box become the hottest? [closed]
An electric heater is placed inside a metal box which has one side open. The diagram shows four possible positions for the box. The heater is switched on for several minutes.
In which position does ...
1
vote
0answers
12 views
I have a slight problem understanding the concept of “work”?
What I understand is that work is not the same as a car using gas or a crane lifting a car high up into the air. Let's use the crane as an example. And let me write out a few lines from the book.
...
-5
votes
0answers
9 views
what types of gravitation have been observed? [closed]
Specifically, if an atom was enlarged to our size(keeping all other mathematical measurement sub-atomic)
Would the electrons follow planet like trajectories
What would these orbits look like to an ...
0
votes
0answers
15 views
Why does the creation operator take a continuum value for the momentum?
Imagine that you have a lattice and a set of masses. Each mass at a lattice point. Now each two neighbouring masses are connected with spring.
Now in Classical Mechanics (CM) the ground state is the ...
0
votes
1answer
36 views
Is it safe for astronaut to do this “dangerous” movement?
So, if the astronaut is working outside the space station in thew space, could he not tie himself onto the space station and if he is going further away of the space station, i think he could just ...
3
votes
1answer
26 views
Goldstone's theorem and massless modes for $\phi^4$ theory
Consider a scalar field doublet $(\phi_1, \phi_2)$ with a Mexican hat potential
$$V~=~\lambda (\phi_1^2+\phi_2^2-a^2)^2.$$
When $a=0$ this is a quartic potential and the symmetry is not ...
-2
votes
0answers
17 views
Relative Quantum Particles [closed]
Being as I started on something similar Here which was closed because the moderators are lazy I have a quick question...
In short
What if a Neutrino Hit another Neutrino and both of these ...
0
votes
2answers
25 views
Under what conditions a person can lift a car alone?
I'm thinking about starting my work of physics with this question but do not know how to answer.
1
vote
1answer
25 views
Why connect cells in parallel?
Say there is a circuit with two 1.5V cells, and a 100 ohm resistor.
If you connect two cells in series, then the total emf is 3V. And the current will be 3/100 = 0.03 A. (Using V = IR):
If you have ...
2
votes
0answers
29 views
Does dark energy affect asymptotic freedom?
If the Hubble constant is extremely large, what will happen with quark confinement?
I guess that quarks will remain confined because of asymptotic freedom. But can gravity or dark energy have any ...
1
vote
2answers
46 views
Solar Eclipse Viewing
I know it is not safe when viewing a solar eclipse to look directly at the sun. I know you can purchase solar eclipse glasses online but how do you make your own solar eclipse glasses that are safe to ...
2
votes
2answers
32 views
Galaxies Center
It is believed (to my understanding) that at the center of all large galaxies are super massive black holes. Why is it then when you see photos of galaxies that the center is extremely bright if a ...
1
vote
1answer
26 views
Are cosmic muons causing mutations or even evloutionary pressure?
As there are experiments studying influence of cosmic rays on organisms,
http://www.ncbi.nlm.nih.gov/pubmed/11541768
I ask my self, if there any influence to DNA from atmospheric muons on the Earth ...
2
votes
2answers
39 views
What's the relationship between an object's color and it's energy?
All else held equal, which has more energy: a violet-painted teacup or a red-painted teacup?
I know that violet light has more energy than red light, but does this mean that the inverse holds true ...
3
votes
2answers
77 views
Discrete version of Feynman path integrals
I've decided to put a very limited amount of my time into understanding the path integral formulation of quantum mechanics. I'm interested in the mathematical formalism more than the physics, so I'd ...
1
vote
2answers
56 views
Can sound be separated from air?
I would like to open up a window in my house, let the air in, but keep the sound out. Could a device be designed to put up on the window, like a screen, and accomplish this?
4
votes
1answer
53 views
The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures?
The speed cannot increase unboundedly of course, so what happens?
2
votes
0answers
31 views
Helium-4 superfluidity and gauge symmetry breaking
Is there an accessible account of superfluidity in Helium-4 as a manifestation of "global gauge symmetry" breaking?
And what is meant by "global gauge symmetry"? I was taught that gauge symmetries ...
0
votes
1answer
35 views
Is a uniformly charged conducting plate the same as a uniformly charged conducting sheet?
Is it correct that a uniformly charged conducting plate is made up of two charged conducting sheets, that is, a charged conducting plate consists of four surfaces?
1
vote
0answers
36 views
Any noise slowly starting to take effects?
I am studying a system subject to random noise, or a system driven by some noise, for example, heat flow or wave propagation perturbed by noise. I would like to know if there is a real system where ...
4
votes
1answer
93 views
can black hole form due to Lorentz contraction? [closed]
Possible Duplicate:
If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?
Imagine, a rod of length L is moving with velocity approach the speed of light ...
1
vote
1answer
41 views
Could ions emitted by an ion thruster represent any realistic danger?
As ion thurster designs improve, the ions emitted could have a velocity (relative to the spacecraft) of well above 10^5 or even 10^6 m/s.
It the likelihood of any such ions ever hitting a human ...
1
vote
2answers
42 views
Why does the light bulb's brightness decrease?
The book said that the brightness of R1 would increase and R2 would decrease. I don't understand this at all.
Why does adding a wire from b to c change anything to R1?
Shouldn't charge still flow ...
4
votes
2answers
60 views
Is the “dimension” in dimensional analysis the same as the “dimension” in “three spatial dimensions”?
When we talk about the dimension of a quantity (e.g. the dimension of acceleration is$[ L \ T ^ {-2}]$) are we talking about the same "dimension" as when we talk about three dimensional space?
Are ...
0
votes
1answer
41 views
Is a low-current electrical arc harmful to humans?
I've heard that electrical flux non-destructive particle testing machines are considered safe because they use less than 2 amps. I have seen an arc created between two objects do considerable damage, ...
4
votes
2answers
85 views
Why don't massive water-borne animals crush under their own weight when they're in water?
If you take a giant whale out of the water and put it on land for long enough, it will crush itself under its own weight. Why doesn't the animal get crushed under its own weight when it's in water?
1
vote
1answer
33 views
Does classical physics predict the effects of shining a laser at a hair?
The discussion on this webpage mentions that shining a laser beam at a hair produces an effect like that of the double-slit experiment. Does classical physics predict the effect you observe when you ...
1
vote
1answer
69 views
Is it possible to have a self-balancing system?
I am trying to create a machine that moves on two points (Wheels or legs). Because of the extremely difficult nature of perfectly balancing the parts, I am wondering is there any way to create a ...
4
votes
2answers
89 views
Does the mass of a body absorbing photons increase?
Let's say I have a photon collector in orbit around the sun. It manages to collect photons perfectly efficiently, that is, without radiating off any energy.
Then, using Einstein's equation:
$$E = m ...
4
votes
1answer
50 views
U(1) Charged Fields
I don't quite understand what is actually meant by a field charged under a $U(1)$ symmetry.
Does it mean that when a transformation is applied the field transforms with an additional phase? More ...
-3
votes
0answers
34 views
What is the x(t) function of dv/dt = av² + bc + c [closed]
how to solve dv/dt = av² + bc + c to obtain x(t) , where a, b and c are constants, v is velocity, t is time and x is position. Boundaries for the first integral are v0, vt and 0, t and boundaries for ...
4
votes
0answers
29 views
Defects in 3+1 TFTs/2+1 CFTs
I would like to know of good pedagogic references to learn about the notion of "defects" in TFTs and CFTs. I am specially interested in 3+1 TFTs (.and probably about their relation to 2+1 CFTs..)
In ...
1
vote
1answer
32 views
Why isn't the force modelled which confines excess charge to remain inside a conductor?
Excess charge placed on a conductor distributes itself on the surface of a conductor. But why isn't the force which confines the charge to remain there, modelled in some way?
2
votes
1answer
53 views
Naive question about massive spin 2 particles and QFT
We know that in order to describe spin 2 massless particles quantum mechanically we need to go beyond the field theory and consider the consistent quantum gravity theory (i.e. superstrings), but to be ...
-7
votes
2answers
81 views
It is possible that the black hole is just a central cavity of a whirlwind of stars?
It is possible that a black hole is just a central cavity of a whirlwind of stars!?
I mean, there is not any heavy object in the galactic center, and actually the black hole is a hole of nothing, ...
3
votes
1answer
71 views
Why do sea levels not rise uniformly around the world?
While reading the article Hawaii’s Beaches Are in Retreat, and Its Way of Life May Follow on The New York Times's website, I was surprised to find out that sea levels do not rise around the world at a ...
7
votes
3answers
147 views
How do they handle energy in magnets at LHC?
I'm guessing that when the LHC ramps up to 4000 GeV this means they are increasing the current in the superconducting magnets as RF fields accelerate the beams. Where does this current go when they ...
-1
votes
0answers
45 views
Consider the rectangle ABCD with the following Dimensions abs(BC)=3 and abs(CD)=4, so, abs(AB+BC+CD)=5 [closed]
[Consider, the, rectangle, ABCD, where \left \| \widehat{BC} \right \|=3 , and, \left \| \widehat{CD} \right \|=4, then, \left \| \overrightarrow{AB}+\overrightarrow{BC}+\overrightarrow{CD} \right ...
2
votes
2answers
48 views
Finding wave-fuctions of a Dirac particle for given 4-momentum and spin 4-vector
I've been reading through various materials on relativistic quantum mechanics, but I find the lack of simple examples disturbing.
I'm acquainted with the general form the solutions to the Dirac ...
4
votes
0answers
76 views
Turbulence parameterization from gravity - fluid dynamics correspondence
I`m looking for a nice introductary reference that explains how the turbulence coefficient or any kind of turbulence parameterization (in view of applications to atmospheric turbulence for example) ...
4
votes
1answer
71 views
Wigner-Eckart theorem of SU(3)
I have just come across the Wigner-Eckart theorem and am not sure on how to apply it. How do I find the matrix elements of $\langle u|T_a|v\rangle$ in terms of tensor components and the Gell-Mann ...
0
votes
1answer
35 views
how to calculate minimum torque a DC motor needs to move the wheels
Im making a robot that must sense objects and pick them up. I need to order some motors, so i wanted to work out the torque needed just to push one wheel (as it may pivot, so one wheel will need to ...
3
votes
1answer
67 views
How do I find the tensor components of all weights of a representation of SU(3), e.g. the six dimensional representation (2,0)
How do I find the corresponding tensor component v^ij of the six dimensional representation of SU(3) with dynkin label (2,0).
2
votes
1answer
51 views
What does the Fermi Energy really signify in a Semiconductor?
In understanding the behavior of semiconductors, I'm coming across a description of the Fermi Energy here and at Wikipedia's page (Fermi Energy, Fermi Level). If I understand correctly, the Fermi ...
1
vote
2answers
107 views
Would you die if you put your hands on a powerline?
You know how birds perch on powerlines without getting electrocuted? What if by some chance that I find myself falling and I grab on one of them? Let's say both of my hands are on the same line, would ...
0
votes
2answers
79 views
Could a solar flare cause the Earth's magnetic poles to reverse?
With all the hype of the impending "2012 Mayan doomsday" I was thinking it might be interesting to see what principles of physics prevent the theories of doomsday from occurring. One overarching ...
2
votes
3answers
105 views
Why does it require such little energy to create the fastest thing in the universe?
I have noticed when I turn on the light switch in my house light comes from the bulb.
How is this light created?(process occurring in the bulb) and why is this small amount of electricity enough to ...
3
votes
2answers
69 views
When work is performed solely by magnetism, is there an equivalent loss of energy from the magnetic field?
When two magnets are placed within appropriate proximity and released, the attractive force will perform work and bring them together. Work is performed overcoming friction. Can we measure a ...
-1
votes
1answer
89 views
Symmetry $\leftrightarrow$ Conservation law
Noether's first theorem states that any differentiable symmetry of the action of a physical system has a corresponding conservation law.
Translation in time (Symmetry) $\leftrightarrow$ ...
1
vote
3answers
36 views
Why does the potential drop across a battery and resistor equal the emf of the battery?
In this diagram you can see the potential difference across the battery and resistor is the same as the pd created by the battery (the battery and resistor are representing a battery with internal ...
