# All Questions

132,902 questions
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### How do I derive a formula for the water level inside a container when it is filled up at a constant flow rate?

When a container (e.g. Vase, Water Glass etc.) is filled up at a constant flow rate the water height changes differently over time depending on the shape of the container. This video shows some ...
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### Relative energy

Suppose a ball is travelling at 5km/h, person A is travelling at 2km/h and person B is travelling at 5km/h in the opposite direction. The ball is travelling at 3km/h relative to A and at 10km/h ...
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### Molecular model of liquids

The macroscopic behavior of gasses and solids follow very intuitively from the description of matter as quasi-spherical molecules interacting with each other with attractive and repulsive forces. ...
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### What is so topological about topological phase transitions?

I am studying the KT-transition, which is called a topological phase transition. The phase transition is driven by vortices in a 2-D superfluid, where it is shown that at a critical temperature $T_c$ ...
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### In static fluid, pressure at same heights are equal. Is this applicable to the oceans?

Generally we consider the reference as horizontal line. But if we consider a vertical water column in the ocean. Then, if we want to consider the reference it should be a circular not a horizontal ...
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### Can I make an inductor coil from covered cables?

I have huge amounts of wires, and it's impossible to remove all the plastic cover off of them. I thought of making the coil just like that, as they are, will it have the same magnetic field or at ...
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### Imaginary part of vacuum polarization tensor

I deal with vacuum polarization diagram calculation with help of QED by Landau et al. and I would like to understand one interesting statement. I know how to compute $\Pi_{\mu\nu}(k)$ via dimensional ...
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### What kind of integration is used in different areas of physics? [on hold]

I'm aware that there are multiple types of integration in mathematics, e.g., there's the Riemann integral, the Riemann-Stieljes integral and the Lebesgue integral, but I'm not privy to their ...
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### With respect to which system are accelerations written in a non-inertial frame?

If $\vec{a}=\vec{a_0}+\vec{a_r}+\vec{\omega}\land(\vec{\omega}\land\vec{r})+\frac{d\vec{\omega}}{dt}\land\vec{r}+2\vec{\omega}\land\vec{v_r}$ being $\vec{a}\to$ absolute acceleration of the ...
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### Strategy for finding flow field for steady, incompressible flow in 2D based on density information

I'm working on a simulation where we wish to determine the flow field for an incompressible fluid based on known values for density at each point. The only outside force is gravity. (Density is not ...
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### Lorentz transformation of vector field

Under a Lorentz transformation, a vector field transforms as: $A'_{\mu}(x')=\Lambda^{\nu}_{\mu}A_{\nu}(x)$ My question is, why is the Lorentz transformed vector field evaluated at $x'=\Lambda x$, ...
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### Determining the pseudo-time period of a system of $n$-pendulums via Kane's method in Python

We can use Kane's method to integrate the equations of motion for a system of $n$ pendulums with arbitrary masses and lengths (see derivation). In particular, if $(x_i,y_i)$ denotes the Cartesian ...
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### Potential from scattering matrix [duplicate]

Given a scattering matrix, is there a procedure to find the potential from the scattering matrix? I think there should be a way as the scattering matrix holds the information of the boundary ...
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### Skin effect prevailing the drift velocity effect

In general, an electron will propagate randomly in a conductor at the Fermi velocity( produced due to thermal energy of the conductor). An applied electric field will give this random motion a small ...
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### What is permittivity at infinite frequency in cole-cole equation?

I am working with estimating the dielectric constant as a function of frequency. I did calculate the S-Parameters from Agilent VNA. The study is similar to this paper When working this, i came across ...
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### Principle of Energy Dispersive x-ray Spectroscopy

I have a question about the EDS I don't understand how the detector can differentiate the Energy of incident x-ray simultaneously. In my thought, the emitted x-ray from the sample have different ...
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### Radial vs tangential component of electrical field due to dipole

I was wondering that why should the maximum magnitude (with respect to $\theta$) of radial component of electrical field of an electric dipole, E_r=-\partial V/\partial r=\frac{2p \cos\theta}{4\pi\...
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### How are fluid membranes stretchable?

The Poisson's ratio of fluid lipid membranes is exactly $\nu=0.5$, because fluids can flow. As answered in this question, under the assumption of a finite bulk modulus $K$, this is the value of $\nu$ ...
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### Proof that electrostatic self-force is zero

Suppose there is a charge distribution in region V and zero charge density outside V such that electric field goes to zero infinitely far away. How to prove that this charged body does not exert an ...
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### Does the distance between the slits, in the double slit experiment, affect the pattern displayed?

Does the distance between the slits affect the pattern displayed? I want a pattern where light parts and dark parts are equal, and I don't want the light parts to be bigger than dark parts.
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### What would happen if the universe had no gravity? [on hold]

My question is what would the universe be like without gravity.
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### Pendulum moving in linear motion [on hold]

Given a diagram below, the linear velocity of the point of rotation is v_linear and the angle that the tension line makes with vertical axis is theta, and its angular velocity theta dot. Assuming ...
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### What is the variance of |S| in Bell's inequality (CHSH inequality)

I found an online exercise that begins with: So far so good. I also found a standard proof of equation (3), but what I did not find is a proof for its variance/standard deviation. The CHSH value |S| ...
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### Statistical model for local polymer concentration

I'm trying to describe the local constraining of two points located on a 2-part DNA polymer (double and single stranded), with respect to one fixed end. See the schematic below: Here I would like to ...
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### Computing Hamiltonian from a matrix formed Lagrangian

I tried to use the fact that Hamiltonian is a Legendre transformation of Lagrangian and thus, H= pq'-L. But I don't understand how to use the fact that Tij is a symmetric matrix, to compute the ...
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### How does an object's volume affect its gravitational pull?

Two instances. An object is in front of two different planets with the same masses, but two different volumes. How does the gravitational pull vary from each planet? I am thinking with more given ...
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### What is the least energy trajectory in Astronomy?

Hi I wanted to know what the least energy trajectory is in relation to astronomy as I can't seem to find a good answer on Google. I want to know because I am trying to answer this question: A ...
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### How much harder is a proton theoretically speaking than a diamond?

It's generally said that a diamond is the hardest substance known to man (apparently there are a few materials known to be harder). However, one ought to expect that a proton or neutron should be ...
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### Where is the present moment in physics?

In an essay in the book, On Space and Time, with contributions by Connes, Majid and Penrose, John Polkinghorne writes in the final essay, titled The Nature of Time: The equations of physics do not ...
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### How can one the find normal force of a block resting on a pool floor underwater?

There is the force of gravity on the block, the atmosphere, the water pressure o top of the block, but how about between the block and the floor? Would we calculate water pressure pushing up from the ...
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### What are soft theorems in context of scalr fields

What are soft theorems ? I tried reading Weinberg’s paper but couldn’t understand it, are there any resources on this ? I am very interested in the case of scalars.
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### If an electron is in an infinite potential well, would it emmit photon when it bounces off the wall?

Let say there is an electron in an infinite potential well. Since it's trapped in the well, I assume (which I'm not sure of whether it's valid to assume such thing) that it will bouce off the wall and ...
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### How does thermodynamics affect our lives? [on hold]

How does the second law of thermodynamics affect our lives? Could we live without the second law of thermodynamics? What is the whole purpose of thermodynamics affecting our lives? I know this is a ...
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### The rate of expansion right after inflation ended

Before inflation occurred, the expansion of the universe was non-inflationary (expanding slower than inflation). What happened to the rate of expansion right after inflation ended? $~$Did ...
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### Calculation of time-ordered propagations and correlators

I am reading the following paper M. H. S. Amin and D. V. Averin, “Macroscopic Resonant Tunneling in the Presence of Low Frequency Noise,” Phys. Rev. Lett., vol. 100, no. 19, p. 197001, May 2008. I ...