5
votes
2answers
21 views

When do phase space functions' Poisson brackets inherit the Lie algebra structure of a symmetry?

I've seen several examples of phase space functions whose Poisson brackets (or Dirac brackets) have the same algebra as the Lie algebra of some symmetry. For example, for plain old particle motion in ...
1
vote
0answers
9 views

Does nature of singularity in black hole depend on material that fell in?

Electromagnetic waves have a tracesless stress energy tensor, and therefore if they are the only fields in a region of spacetime, the Ricci curvature scalar $R=0$ according to GR. However $R^{\mu\nu} ...
2
votes
1answer
120 views

Feynman's derivation of Bernoulli (part of it)

OK, so what's up with the $\Delta M$ here? I don't get it. In fact, my textbook doesn't even put it in. I don't think it is a type-o because he continues on with the explanation. If anything I got ...
0
votes
1answer
17 views

Error in measuring distance ignoring curvature of Earth

Suppose you model distance as a flat 2d plane rather than a curved surface. Given that the radius of the Earth is about 6400 km, approximately how far must you travel before the relative error ...
0
votes
1answer
4 views

Binding Energy of an Electric Dipole

My question is structured in two parts: Is there any way to isolate the charges of an electric dipole? What is the binding energy of an electric dipole? To put it in another way, is there ...
5
votes
4answers
5k views

is it possible to flow current in open circuit?

First , i don't know much about chemistry and physics. I'm just a graphic designer but i have this question in my mind. I'm sorry if this question is too basic and use 'generic' language. As i know ...
0
votes
1answer
8 views

Propagation of sound waves and monopole

While it is understood that in order for the acoustic waves to reach far field the wavelength should be less than the characteristic length of the source, I am not able to physically understand how? ...
2
votes
2answers
23 views

Heat generated by collision

Suppose there are two objects: A = m1 and B = m2 . A is travelling at a constant velocity v toward B and collides inelastically: is there a way in which I could determine the energy which is ...
2
votes
2answers
319 views

Calculating air density lapse with altitude (specifically, pressures)

This might be a bit more of an engineering question, but I'm calculating air density drop-off with altitude, and I'm having some problems calculating the pressure (I'll run through my method). This ...
4
votes
2answers
60 views

Newton's Third Law Exceptions?

Lately I've been brushing up on some of my old Physics texts from college. Most recently, I've been rereading parts of "Classical Dynamics of Particles and Systems (5th ed.)" by Thornton and Marion. ...
48
votes
2answers
2k views

Why does my wooden door disperse light into a rainbow color spectrum?

On a clear morning, light comes through this window (viewed from the inside) It then hits the door on the opposite side (so viewing from the outside the door straight on the other side) There is ...
2
votes
2answers
169 views

Projectile motion maximum distance to origin

Is there an elegant or easy way to derive the maximum distance from the origin to a point of the parabola created by projectile motion (assume initial position is the origin)? Other than ...
0
votes
0answers
13 views

Radar Vs. Sonar

What is the true difference between radar and sonar? My understanding is that radar uses a reflected EM wave, while sonar uses a compression (shock wave) of the material it's in. (It compresses water, ...
-1
votes
0answers
16 views

Find the smallest turning radius of a car, given velocity [on hold]

So, here's another homework question... A sports car is advertised to be able to "reach 60 mph in 5 seconds flat, corner at 0.85g, and stop from 70 mph in only 168 feet." At 60 mph, what is ...
0
votes
1answer
9 views

Various springs acting on a point mass

The force exerted on one spring is $\vec{F}=-k\vec{r}$. Now suppose we have N slinkys with stiffness $k_1,k_2,k_3,...,k_N$ where they have one end tied to fixed points in space with coordinates ...
0
votes
0answers
4 views

(Chemistry) Dimensionless heat transfer coefficient

I'm trying to reproduce in Matlab the model of a continuous stirred tank reactor (CSTR) that I've gotten for a project. The model is written in the state space and uses some dimensionless values, ...
1
vote
2answers
112 views

Does the formula $ \theta = \frac{v}{c} $ to find out deflection of light make sense?

I read in reliable sites that GR and classical physics calculate the angle of deflection in the same manner. The formula is almost identical: $$\theta = \frac{4GM}{c^2*r} \rightarrow \frac{4GM}{c*r} = ...
0
votes
1answer
21 views

Annihilation operator on Fock space

I agree that $$\hat a|0\rangle=0$$ But then, based on the above, the following should hold $$\hat a_k |N_1,...,N_{k-1},0,N_{k+1},...\rangle=|N_1\rangle\oplus\cdots\oplus |N_{k-1}\rangle\oplus \hat ...
-1
votes
0answers
21 views

Why del operator is called divergence operator?

I know the Del operator is called divergence operator. And -Del is called convergence? Please explain why with an example.
2
votes
3answers
161 views

Joules to do something

If my very limited understanding is correct, then, not accounting for gravity: 1 Newton can move 1 kilogram 1m But, can 2 Newtons move 1 kilogram 2 meters? Is this because 1 Newton = acceleration ...
0
votes
1answer
22 views

How come we talk about gravitational potential energy and not gravitational potential?

With regards to gravity the equation learned is $$U=-\frac{GMm}{r}$$ And the relationship to force is $$F=-\frac{dU}{dr}$$ In electrostatics we instead talk about electric field and electric ...
4
votes
1answer
91 views

Is that a result of thin-film interference?

Several years ago, I was laying on my bed and had a CD shaped transparent plastic disk (which was covering a 100 CD stack), basically a transparent CD. I don't know why but I took my phone and took a ...
6
votes
2answers
176 views

Why is fundamental physics taught in terms of particles?

According to this paper, there can be no relativistic quantum theory of localizeable particles ("relativity plus quantum mechanics exclusively requires a field ontology"). Sean Caroll has also argued ...
5
votes
2answers
436 views

Why do rockets jettison fuel tanks?

I'm trying to understand why rockets have multistages releasing their fuel tanks. Say a rocket $R$ has two fuel tanks $A$ and $B$, which respectively have masses $m_a$ and $m_b$, and the mass of the ...
0
votes
0answers
7 views

Radiometric dating of lithosphere and the Schwarzchild's critical radius

It is reported that the earth's lithosphere is constantly recycling over time. If that is so, then would this alter the validity of radiometric dating? It is theorized that a singularity the size ...
1
vote
1answer
81 views

Why do some bound states disappear in a discontinuous way?

Generally, we have the picture that as the parameter (say, the depth of a trap) of a system varies, the bound state gets more and more extended and disappears eventually at some critical parameter ...
2
votes
2answers
40 views

Question relating to energy transfer in between two particles

How would I go about calculating the maximum kinetic energy transferred from one particle when it forms an elastic collision with another particle. For example, if I had two billiards one with mass m ...
3
votes
1answer
44 views

How do gas molecules constantly bounce without losing energy?

From a related question (How does pressurized gas constantly push?), i asked myself this: How do gas molecules constantly bounce off each other without losing energy? If you drop a ball, it bounces a ...
2
votes
0answers
37 views

Fitting two semicircles in a Nyquist plot? [closed]

I have done some impedance spectroscopy fist time recently and got the following [Nyquist plot](http://en.wikipedia.org/
0
votes
1answer
20 views

Uncertainty principle in Harmonic Oscillator

In a single particle Harmonic Oscillator, suppose I prepare it in the ground state and then measure its position. From the relation connecting Total Energy, Kinetic energy and Potential I can ...
1
vote
0answers
16 views

Velocities of waves (such as visible light, and radio)

The speed of light in a vacuum is a constant 299,792,458 m/s. In water, it is much slower. Does this happen to such waves as radio, or X-ray? (Would say, a 3 meter wavelength travel slower in air than ...
1
vote
0answers
11 views

Where can I find phase diagrams for mag-thor alloys?

Where can I find phase diagrams for Mg Th alloys? Thanks!
1
vote
1answer
26 views

Understanding the energy transffered/used from a power source?

A source of power(from a generator,battery,etc...) is used to power a system of any kind. We can calculate the energy used via this formula $E$ = $IV$ x $t$ ? For example, a battery that is connected ...
4
votes
2answers
92 views

When does a singularity start to exist during a black hole formation?

Excuse me if the question is naïve. I am not a physicist. Let's imagine formation of a black hole from a homogeneous collapsing star. At certain moment when enough of matter is inside of a small ...
1
vote
1answer
50 views

Physical simulation in python

Is there a "standard" python package used to aid in physical simulations? What is the most popular? edit: perhaps I should have worded this question differently. Something more to the effect: Could ...
1
vote
1answer
39 views

Physical Meaning of Divergence of Convective Velocity Term

When taking the divergence of the convective velocity term, I get the following: \begin{align} \nabla\cdot\left[\mathbf u\cdot\nabla\mathbf u\right]&=\frac{\partial}{\partial ...
0
votes
1answer
46 views

Which function denotes the energy of thermal motion within a system?

In thermodynamics, the heat $Q$ is defined as a type of energy in transfer, and is not a state function, which function denotes the energy of thermal motion within a system? 1) $TS$, (there is a ...
-1
votes
0answers
20 views

Quadrature method (vertically falling particle) [on hold]

Consider a particle, that in the presence of the force of gravity, moves only vertically. Obtain the equation of motion of the particle from its mechanical energy(quadrature method). Consider the ...
1
vote
0answers
11 views

Boundary Conditions for axisymmetric stream functions in a pipe

I'm solving the equation $$ \frac{\partial^2 \psi}{\partial r^2}+\frac{\partial^2 \psi}{\partial z^2}-\frac{1}{r}\frac{\partial \psi}{\partial r} =-\omega_\phi $$ in a cylindrical pipe, where ...
0
votes
1answer
22 views

Semiclassical approximation in Quantum Field Theory

I've recently stumbled upon a semiclassical approximation to quantum field theory that I've never heard of and have a hard time understanding. Consider the Hamiltonian, \begin{equation} H = \frac{c}{ ...
0
votes
1answer
21 views

Should S always be more than 2 to violate CHSH inequality?

Is it always should be about $2\sqrt{2}$ or it's just a maximum value and it's possible to measure something like S = 1.90, 1.8, 2.0, 2.4, 2.6, 1.8 (with average = 2) in different sub-experiments to ...
1
vote
2answers
44 views

Has energy in 'transit' been incorporated into missing matter calcs.?

Has energy in 'transit' been incorporated into missing matter calcs. ?It would seem that, although very small in mass, the sheer number of particles shhoting about from one end of the universe to the ...
6
votes
2answers
250 views

Square of the Pauli matrices and the identity matrix

The square of any of the three Pauli Spin matrices is equal to the identity. Is there any physical meaning to this? Would you expect it? Maybe in the context of the $SU(2)$ group?
3
votes
1answer
40 views

Why can we leave off half of the general solution?

In this pdf, it says at the bottom of the first page and beginning of the second: ... whose solution is: $$\Psi(\theta) = c_1 e^{i\omega\theta} + c_2 e^{-i\omega\theta}$$ Since we are ...
1
vote
2answers
232 views

Calculating the change in entropy in a melting process

I have a homework question that I'm completely stumped on and need help solving it. I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
1
vote
1answer
36 views

Finding expectation value of $p^2$ without integrals

So the expectation value of momentum, if you know the expectation value of position is $$\langle p \rangle = m \frac{d\langle x \rangle}{dt}$$ Is there a nice formula like this for $\langle p^2 ...
2
votes
2answers
39 views

$ε_0$ affects electric field intensity, but $μ_0$ doesn't affect magnetic field intensity?

I'll be honest: this question is actually a homework problem. I've spent the past hour going through Google and several textbooks trying to answer the question "Why does $ϵ_0$ affect electric field ...
4
votes
2answers
120 views

FRW metric and its validity througout the age of the universe

Why do we think that the FRW metric should be valid throughout the entire history of the universe?
2
votes
1answer
151 views

If distant observers never see a black hole form in finite time how can the information paradox be a problem?

So, at least as reported in the media, the physics community is still struggling with the problem of resolving the impossibility of retrieving information from beyond the event horizon of a black hole ...
0
votes
1answer
21 views

Potential Difference between two glass spherical shells [on hold]

Say I have two spherical shells, let's call them sphere 1 and sphere 2. Sphere 1 has a uniform charge of +Q and sphere 2 has a uniform charge of -Q. Sphere 1 and sphere 2 are separated by a distance ...

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