0
votes
0answers
2 views

Explanation of quote from Steven Weinberg

When skimming through a book, I found this quote: The universe is an enormous direct product of representations of symmetry groups. —Steven Weinberg I am a mathematician (so I know only basic ...
0
votes
0answers
2 views

With what frequency triangle swings if it shuns from equilibrium?

Guide V-shaped is with no friction in the swivel bearings A and B (see Fig.) Of the magnet with a vertical magnetic field of 0.8 T. The weight of the guide is 50 g, the length AB 4 cm, and the length ...
0
votes
2answers
14 views

How do vinyl records work?

I know that vinyl records save the sound as ups and downs on the record plate surface. Let's say two people with different voice timbers say "I like vinyl records" with the same level of voice. It ...
1
vote
1answer
35 views

Speed of light paradox

If I send two rockets from the Earth in opposite directions, at, say, 60% of the speed of light relative to the Earth, then relative to each other they are travelling at 120% of the speed of light. ...
0
votes
0answers
8 views

Calculating curvature of spacetime when energy is present

I am only about half-way of studying SR and GR and I am not yet familiar with a formula to calculate the curvature of spacetime when energy is present. To be more specific, I want to calculate ...
1
vote
0answers
4 views

What is the value (order of magnitude) of electric charge density of the atom and the nucleus?

The mass density of the nucleus is constant. But what is the electric charge density of the nucleus and the atom (any order of magnitude)?
0
votes
0answers
12 views

How to count the symmetric wavefunctions made by 6 (u, d, s, $\bar{u},\bar{d},\bar{s}$) quarks to form Baryons (i.e., 3 particle state)?

Peskin said 6 (particles + Anti-Particles) guys make (6($\Rightarrow $particles) x7x8)/(3x2)= 56 total symmetric state. How?
1
vote
1answer
6 views

does the internal energy and enthalpy of the GAS changes in a free expansion process?

when a balloon kept in an evacuated room is punctured and the ideal gas in the balloon goes on to fill the entire room,does the gas perform any work in this expansion, and is there in any change in ...
1
vote
1answer
12 views

'Doppler redshift' Vs 'Cosmological redshift'

It is not difficult to understand the differences between 'Doppler redshift' and 'Cosmological redshift' conceptually. But how do astronomers distinguish them when doing observations?
0
votes
2answers
25 views

How much is if my internet provider says “we have increased your WiFi connection by 2 decibels”?

I understand the definition of decibel as a logarithmic unit for intensity of anything. I just cannot imagine its "actual size" when comes to the wireless connection. Can you provide something ...
0
votes
0answers
12 views

Why wouldn't any Emission Theory work?

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins_pathway/#Emission Here, at the Emission theories of light, I loved the discussed theory. There seems to be a contradiction right ...
0
votes
0answers
7 views

Reverse polarity vs falling in Millikans experiment

There are multiple methods of hot to perform Millikans oil drop experiment. One of them lets the drop rise through an electric field (and measures the velocity) then lets if fall (without an electric ...
0
votes
1answer
20 views

Acceleration of uncharged particles

Following on from this comment - do uncharged particles radiate under acceleration? (no offense to the commenter, just clarifying as I've not heard of this before) Why is this? I vaguely recall a ...
0
votes
1answer
21 views

Absoluteness of Simultaneity

I think this is a very important question because if simultaneity is absolute, then it shakes the foundation of relativity. But it was asked here a month ago, and no one answered it. Neither does ...
0
votes
1answer
29 views

Question about scalar product of 2 four-vectors

I'm looking for help to prove that $\mathbf{a\cdot b}=-ab\ cosh \ \theta$, where: $\mathbf{a}=\sqrt{\mathbf{-a\cdot a}}$, $\mathbf{b}=\sqrt{\mathbf{-b\cdot b}}$, and $cosh \ \theta$ is $\gamma$, ...
0
votes
0answers
24 views

Photograph of Light as Wave and Particle

what is this? actually its the first photo of light as wave and a particle. The bottom "slice" of the image shows the particles, while the top image shows light as a wave. i have questions 1.how ...
0
votes
0answers
12 views

Coulomb barrier in nuclear fusion

Suppose there exists an alpha particle in the nucleus. Within a radius of 2 femtometer, the dominating force is the nuclear force but beyond this radius, the Coulomb force becomes the effective ...
0
votes
2answers
28 views

Are spherical coordinates distances or angles?

I've become confused about spherical coordinates when dealing with electric fields. The way I always understood spherical coordinates is something like the below picture. To define a vector, you give ...
0
votes
0answers
9 views

Derivation of the kinetic energy of decay product

By conservation of momentum: $$M_{\alpha }V_{\alpha }+M_{Y}V_{Y}$$ By the conservation of energy: $$(\frac{1}{2})M_{\alpha }V_{\alpha }^{2} + (\frac{1}{2})M_{Y }V_{Y }^{2}$$ Here I begin the ...
0
votes
0answers
13 views

Klein paradox in graphene

When considering the Klein paradox in graphene Katsnelson, Novoselov and Geim introduce a potential barrier (see http://www.nature.com/nphys/journal/v2/n9/full/nphys384.html). But I cannot understand ...
0
votes
1answer
24 views

Maxwell, speed of light and the electric permittivity and magnetic constants

When Maxwell found that the already-measured speed of light could also be derived from the already-measured electric and magnetic constants, what were the electric and magnetic constants measured to ...
1
vote
2answers
43 views

Why can velocity and acceleration be negative?

Why is speed and acceleration negative when $V_1$ of an object is say 150m/s, $V_2$ is 0 m/s and $\Delta d=0.50\,\rm m$? I found the time it takes which is 0.0033s and the acceleration to be 90909.09 ...
0
votes
0answers
27 views

Is it more effective to skim through a topic then go back for details or deeply understand each concept/equation before moving on?

For example, you are going through a textbook chapter on rotational motion. You come across the concept of moment of inertia and the relevant equations for the first time. You could skim over moment ...
0
votes
1answer
46 views

Conceptual question regarding work

Here is a problem I am having some trouble with: The solution is below, my question is, why is conservation of energy valid in this situation. From my understanding, just before the box hits the ...
2
votes
5answers
88 views

Why does moving electron emits photons?

I have read that moving or oscillating electron emits photons. But why and how does it so? And why only photons? There are other bosons like gluons, W and Z bosons, so why does electron emit only ...
0
votes
2answers
20 views

Collsion in 2D, find angle and final momentum

Suppose that the collision is inelastic. Disregard friction as the surface is smooth. Suppose that one is in the direction of $(1,0)$ and the other $(0,1)$. Is the final momentum the vector addition ...
0
votes
1answer
49 views

How to prove that any rotation can be represented by 3 Euler angles

How can one prove that any rotation of a rigid object in 3-dimensional (3D) space can be represented by a sequence of three rotations around pre-fixed axes by 3 Euler angles? I see this statement in ...
2
votes
2answers
53 views

Solution of simple problems using only Maxwell equations in differential form

Solve simple electrostatic or magnetostatic problems using only Maxwell equations. For example: In every book there is an excercise to find a magnetic field outside a thin wire of radius $a$ with ...
0
votes
0answers
19 views

finding velocity of solid particle right after collision

If a particle collides with a droplet, depending to magnitude of their velocities, different scenarios might happen: rebound, penetration, disintegration, etc. If particle starts penetrating into ...
5
votes
1answer
55 views

Why did the matter in the early universe not stick together due to gravity?

(Feel free to correct any mistaken assumptions I have) The overall question I have is: given that the early universe started as an incredibly dense ball of matter and energy, why didn't that mass ...
0
votes
0answers
14 views

Seeking Reference on Transport of Momentum by Diffusion of Mass

I'm looking at continuum mechanics from the perspective of De Groot and Mazur's "Non-Equilibrium Thermodynamics" - the first reference that I've come across that seems to do a good job of bringing ...
1
vote
1answer
19 views

Non-linear relationship between power supplied and perceived brightness in a filament lamp?

I was expecting the relationship between these two to be linear, but after conducting an experiment my data fits almost exactly on the curve, $y = 2800.2 x^{2.0173}$, where $y$ is the brightness in ...
0
votes
1answer
29 views

Athletics on the moon

The moon is a lot smaller than the earth ($\frac{1}{81}$ of the mass and $\frac{3}{11}$ of the diameter). a)How high would a professional vaulter jump on the moon? Assume that he would jump ...
0
votes
0answers
25 views

Quantum dimensions in SU(N) level k Kac-Moody current algebra

The CFT of the SU(N) level k Kac-Moody current algebra has many Kac-Moody primary fields. I wonder if any one has calculated the quantum dimensions of those Kac-Moody primary fields. I know that, for ...
0
votes
0answers
46 views

Halley's comet. (Questions from a visiting astronomer)

Okay, so we had an apparently famous astronomer in class today. He is giving lectures at our university this week and my class is one of them. So he just comes in on his first day and ends his ...
0
votes
0answers
12 views

Electron confinement energy

I was introduced the electron confinement energy. At room temperature thermal energy of a particle is about $k_B T$, where $T=298K$, giving about $25meV$. I was told that $E_{confinement}=50emV$, ...
0
votes
2answers
21 views

Does the Photoelectric Effect cause any kind of decay?

From my understanding, the Photoelectric Effect knocks electrons off of some metal using photons. Since electrons are being thrown out of the metal, does this cause some kind of decay?
1
vote
0answers
11 views

Nuclear powered flux compression generator?

A flux compression generator is a device for converting the chemical energy of explosives into magnetic field energy, with reported efficiencies of up to 20%. Is there a limit on the conversion ...
-1
votes
0answers
21 views

Central Force - Trajectory

There is a central force $\vec{F}(\vec{r})=f(r)\vec{e_r}$. 1.1.: The trajectory/flight path is defined by $r=r(\phi)$, compute $f(r)$. 1.2.: The path is defined by $u=u(\phi)$ with ...
0
votes
1answer
31 views

Explanation of Interference of Electromagnetic Waves

There is a question on a test which goes like this: "Given two electromagnetic waves, one of wavelength 6.0 X 10-7 m and the other of wavelength 7.0 X 10-7 m, travelling in space. When the two ...
0
votes
2answers
35 views

'schrodinger' picture in measurement based topological quantum computation

I am looking at the measurement processes in topological quantum computation (TQC) as mentioned here http://arxiv.org/abs/1210.7929 and in other measurement based TQC papers. Let's say I start with ...
1
vote
1answer
22 views

Coriolis Effect vs airplane

So, if I build a highway from north pole towards equator and sit in a car, speed pretty fast towards it, I should feel force with the Earths rotation due to the different rotation speeds of this ...
-3
votes
1answer
23 views

Overloading stresses wooden planks beyond their elastic range, causing them to fail?

With safe use there is the fact that a car (a not so light load) can board a ship successfully going over two wooden planks. On youtube one can see this by a car boarding a ship going over two wooden ...
-6
votes
0answers
28 views

My own thoughts about singularities and spacetime [on hold]

I believe the assumptions about black holes are mostly wrong due to the idea that time dilates relative to an outside observer as you get closer to the singularity at the center of the black hole. ...
0
votes
0answers
10 views

Bethe lattice nn Ising model - phase diagram

How does phase diagram for nearest neighbors ising model looks like?
3
votes
3answers
91 views

Physical reason why the derivative of a wavefunction has to be continuous?

Question What is the physical reason (i.e. without any maths) that the derivative of a wavefunction (except with infinite potentials) has to be continuous? Other info I know that in the classical ...
1
vote
1answer
45 views

If time-like paths are geodesics, what physical principle applies to space-like intervals?

If I have a number of particles interacting with one another locally, then the center of mass of the system moves along a geodesic. Taking this further with the particles interacting via an EM field, ...
-2
votes
0answers
20 views

How to make wormhole? [duplicate]

Today in my Physics Class, My teacher gave us an introduction of relativity and I found this very fascinating. He Said that its very hard to make a wormhole because it requires a lot of energy. I am ...
2
votes
1answer
11 views

Effect of small changes in atmospheric pressure on open cylinder piston

OK, I'm not a physics student, but I played one for 2 semesters 35 years ago... now I'm a competitive shooter working a theory about why small changes in atmospheric conditions cause our hyper-tuned ...
0
votes
1answer
22 views

Torque in a non-inertial frame

How can we calculate torque in a non-inertial frame? Take for instance a bar in free fall with two masses, one on either end, $M_1$ and $M_2$. Taking the point of rotation to not be the center of ...

15 30 50 per page