0
votes
1answer
7k views

Finding Phase angle of Simple Harmonic Motion?

A sinusoidal oscillator has : $$x=x_{max} \cos(\omega t - \varphi )$$ Period is 2, initial displacement is 100mm initial velocity is 200mm/s What is the phase angle assuming $-\pi < \varphi < ...
6
votes
1answer
174 views

What is the orbital path of Omega Centauri?

I was under the impression the only objects relatively close to our Milky Way but not yet a part of it were the Sagittarius Dwarf and Large and Small Magellanic Clouds and then much further out, but ...
2
votes
1answer
120 views

How can I calculate the amount of bubbles needed to lift a submerged body?

Our teacher had us come up with our own thermodynamics experiments, so I put a glass of water inside a vacuum-capsule. Inside the glass of water I have placed a non-floating object, a small plastic ...
3
votes
1answer
309 views

Showing constraint is nonholonomic

One example of a nonholonomic constraint is a disk rolling around in the cartesian plane that is constrained to not be slipping. These leads to the constraint $dx - a \sin\theta d\phi = 0$ and $dy - ...
12
votes
3answers
525 views

Do particles have different spins in different frames of reference?

Let's say we have two photons, whose momentum vectors point to opposite directions. Also spin angular momentum vectors of the photons point to opposite directions. (Sum of spins is zero) Now we ...
2
votes
2answers
3k views

How the pipes of water don't freeze in -40 celsius?

Does anyone have a good answer how comes that the water in the pipes in our houses doesn't freeze even if it is -40 celsius for a whole week? of course assuming we don't make the water to fluid in it
2
votes
1answer
229 views

Asynchronous generator run in vacuum chamber

what will be happen if we put asynchronous generator in vacuum chamber & run it above its synchronous speed. After reaching its over synchronous speed we will cut off electrical supply. Can it run ...
-3
votes
1answer
194 views

True or false? Particle physics [closed]

It is not possible to prove the point of origin of a photon It is not possible to prove the point of origin of a free electron It is not possible to prove that protons or neutrons exist inside a ...
2
votes
1answer
120 views

What's the meaning of the coupling change after a renormalization (in the 1-dim Ising Model)?

What does it mean that after the theory (1-dim Ising model here, but the question is general) is renormalized one time and $g_i\rightarrow g_i'$, that the couplings are weaker, even if the theory ...
1
vote
1answer
2k views

When the electric field in an electrostatic charged conductor is zero, is the potential within also zero?

Let's say you have a point charge inside a conducting shell with an inner radius of 5cm and an outer radius of $7cm$. The point charge has a chard of $-4C$ and the shell a charge of $6C$. This means ...
1
vote
1answer
128 views

Will timbre/quality be different if two different people play the same guitar? [closed]

Will timbre/quality be different if two different people play the same guitar? Assume that frequency/pitch and amplitude are same.
3
votes
1answer
3k views

Confused with stress, strain and linear thermal expansion

Four rods A, B, C, D of same length and material but of different radii r, 2r , 3r and 4r respectively are held between two rigid walls. The temperature of all rods is increased by same ...
0
votes
2answers
158 views

The time for which rear moving block remain in contact with spring in the following situation? [closed]

I'm a physics tutor. I'm stuck up with this question. I've no clue about how to proceed with this question. Can any one help? A 2 Kg block moving with 10 m/s strikes a spring of constant π^2 N/m ...
0
votes
2answers
933 views

Help me find electric field strength vector for this given equipotential line

I'm a physics tutor. This is the question from a High school book. The equation of an equipotential line in an electric field is y = 2x, then the electric field strength vector at (1, 2) may be ...
0
votes
2answers
1k views

The energy of electric interaction between these dipoles? [closed]

I'm a physics tutor. This is not a homework problem. I'm unable to solve this problem. The energy of electric interaction between these dipoles will be: Choose the correct answer from: I tried ...
0
votes
1answer
5k views

Why are umbrellas black?

Why are umbrellas specifically in black? Of course we do have colored ones, but black is the majority. Is there any scientific reason behind it?
4
votes
1answer
489 views

Can we solve the particle in an infinite well in QM using creation and annihilation operators?

The particle in an infinite potential well in QM is usually solved by easily solving Schrodinger differential equation. On the other hand particle in the harmonic oscillator oscillator potential can ...
8
votes
3answers
116 views

Constructing a Hamiltonian (as a polynomial of $q_i$ and $p_i$) from its spectrum

For a countable sequence of positive numbers $S=\{\lambda_i\}_{i\in N}$ is there a construction producing a Hamiltonian with spectrum $S$ (or at least having the same eigenvalues for $i\leq s$ for ...
2
votes
3answers
1k views

Shielding magnetic field without mu-metal

I need to shield my device from magnetic interference, including earth magnetic field (if you move device around, it might be enough to cause slight currents i guess) and magnetic field caused by ...
0
votes
3answers
300 views

Light Rays that are Perfectly Parallel

I just heard this simple reasoning in a documentary film: Light rays from distant stars are perfectly parallel. This is pretty interesting thought. In nature, it is hard to find something really ...
3
votes
1answer
177 views

Do mass and the Pauli exclusion principle conspire to make light fermions take up more space?

The wavelength of light fermions is longer. Wouldn't this cause them to take up 'more space' so that they didn't overlap according to the Pauli exclusion principle? Am I totally misunderstanding ...
8
votes
2answers
264 views

Irrelevance of parastatistics for space dimension > 2

Consider a system of $n$ undistinguishable particles moving in $d$-dimensional Euclidean space $E^d$. The configuration space is $M=((E^d)^n \setminus \Delta)/S_n$ where $\Delta$ is the diagonal ...
0
votes
1answer
135 views

How to find the orbit of a moving point object given 3 past passing positions?

How do I find the orbit of a moving point object given 3 past passing positions and the tangents at these passing positions, and given that the orbit is known to be an ellipse?
8
votes
1answer
188 views

Do thermodynamic quantities in CFT correspond to something different in AdS/CFT?

From what I've (hopefully) understood from the AdS/CFT correspondence, physical quantities have a dual version. For example, the position in the bulk is the scale size (in renormalization), and waves ...
6
votes
0answers
210 views

Are there known turbulent nonlinear equations where the cascade is a thermal gradient?

In a recent answer (here: The equipartition theorem in momentum space ), I suggested that if you have an appropriate first order equation (in the answer I used a second order equation, but it is more ...
3
votes
2answers
3k views

If I move a long solid stick can I send message fastest than light? [duplicate]

Possible Duplicate: Is it possible for information to be transmitted faster than light? I mean by using a perfect solid stick long enough and moving it forward and backward can I send ...
4
votes
1answer
294 views

Stability of moons around tidally locked exoplanets

Can someone send me pointers to work (either theoretical or simulations) showing (in)stability of satellite orbits around tidally locked exoplanets? I want to know firstly if satellite orbits can ...
5
votes
3answers
2k views

What's the difference between “boundary value problems” and “initial value problems”?

Mathematically speaking, is there any essential difference between initial value problems and boundary value problems? The specification of the values of a function $f$ and the "velocities" ...
1
vote
2answers
4k views

Calculating Impact Velocity Given Displacement and Acceleration

Assume a car has hit a wall in a right angled collision and the front bumper has been displaced 9 cm. The resulting impact is 25g. Also, it is evident by skid marks that the car braked for 5m with ...
2
votes
1answer
305 views

Reynolds number with hyper-viscosity

Is it possible to evaluate a Reynolds number when viscosity operator is substituted by hyper-viscosity operator at the power H (Laplacien to the power H) in the incompressible Navier-Stokes equations ...
2
votes
0answers
331 views

A solvable model for the finite rectangular potential well with a bump in the middle

A well known example in quantum mechanics is that of a finite rectangular potential well with a rectangular bump in the middle. I guess this closely approximates the "umbrella" effect of the $NH_3$ ...
2
votes
0answers
500 views

kinetic energy in collisions [closed]

We were hoping you could help us understand collision energy. Vehicle $ A $ is driving West at $35\space mph$ and weighs $ 1437 \space kg$. Vehicle $ B $ is driving North at $35\space mph$ and weighs ...
7
votes
2answers
796 views

How does non-Abelian gauge symmetry imply the quantization of the corresponding charges?

I read an unjustified treatment in a book, saying that in QED charge an not quantized by the gauge symmetry principle (which totally clear for me: Q the generator of $U(1)$ can be anything in ...
3
votes
1answer
263 views

What is the Correlation Between Solar Wind Velocity/Density and Sunspot Count?

We have the Advanced Composition Exporer (ACE), which orbits in the L1 libration point as a source for solar wind velocity and density (particles/cm^3) data. Typically, at a velocity in the range of ...
3
votes
2answers
3k views

Good quantum physics textbooks [duplicate]

Possible Duplicate: Learn algebra and interpretation of QM I'm a physics student it's my last year and I find my self struggling with usage of quantum mechanics. Now I'm starting to learn ...
3
votes
2answers
286 views

Proposed Closing of Alcator C-Mod Fusion Tokamak

So I have friends at school who are petitioning against the proposed closing of the tokamak (refer to the recently released FY 2013 Administration Budget). I told said friends that before I signed the ...
2
votes
1answer
422 views

Contraction of indices

We use contraction of indices method to manipulate Tensors. However, I cannot relate that manipulation visually. We can change covariant tensor to contravariant tensor and vice versa by contracting ...
9
votes
4answers
504 views

Did really everything begin with a state with very low entropy?

As emphasized by Penrose many years ago, cosmology can only make sense if the world started in a state of exceptionally low entropy. The low entropy starting point is the ultimate reason that the ...
0
votes
1answer
866 views

Increase of threshold current by temperature in a laser diode

I read somewhere that if we increase the temperature of the material in a laser diode the threshold current for lasing also increases. Can someone explain to me why is this happening? What is the ...
2
votes
2answers
1k views

How do swimfins work?

I'm interested primarly on bifins (one fin for each foot) with a monofin movement, e.g. undulatory. I'd like to know how they work and where I can find articles/books about it.
1
vote
2answers
205 views

Can a complex lens be represented by wavefront aberrations?

Usually complex lenses are described by their geometric design - usually a sequence of spherical cap sufraces and materials. The lens behavior, ie. how it transfers rays, can be evaluated by ray ...
4
votes
1answer
179 views

What is the definition of precession (in the context of Spinors)?

What is the definition of "precession"? How is it applicable to abstract objects such as Spinors? I understand the mathematics, but don't understand what one means by "precession angle" etc when it ...
2
votes
1answer
290 views

What is meant by the rest energy of non-composite particle?

When talking about the rest energy of a composite particle such as a proton, part of the rest energy is accounted for by the internal kinetic energy of its constituent quarks. But what is physically ...
1
vote
2answers
405 views

Connection between momentum and energy

What is the connection between momentum and energy? Which of the answers is the correct? A particle can have zero momentum but energy. A particle can have zero energy but momentum. ...
-1
votes
2answers
262 views

Need help buying binoculars online for astronomy (10x50) [closed]

After reading much online I've decided to by a 10x50 porro prism Binoculars. The one I have in mind http://www.letsbuy.com/celestron-upclose-10x50-p-34652 has BK7 prisms. The one I would like to buy ...
2
votes
1answer
1k views

Angular frequency. Wrong interpretation at Wikipedia?

This and this articles mention that the angular frequency is: number of oscillations per unit of time But this doesn't seem to be correct since the angular ...
47
votes
1answer
10k views

Why does a window become a mirror at night?

In day, when you look in the room through the window out, you can clearly see what happens outside. At night when it's dark outside but there's light inside you can look in the window but it becomes a ...
8
votes
2answers
860 views

Visualizing Ricci Tensor

By definition Ricci Tensor is a Tensor formed by contracting two indices of Riemann Tensor. Riemann Tensor can be visualized in terms of a curve, a vector is moving and orientation of the initial and ...
3
votes
1answer
325 views

role of pure mathematics in fusion?

Is there any way a pure math guy can get his rigorous math fix while simultaneously moving fusion research forward? Is fusion simply too complicated to take a pure math approach? What open math ...
1
vote
0answers
477 views

Is the $mL_c$ value for triangular and rectangular fins the same value?

I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong. ...

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