3
votes
0answers
477 views

Movie Interstellar - Followup Question to Escape Velocity

Continuing the discussion on this thread: Movie Interstellar - Question about Escape Velocity The movie Interstellar shows people on a water planet where time is dilated so much that 1 hour is equal ...
0
votes
1answer
41 views

Can you heat something in AL foil using IR?

Is it possible to heat up, let's say, a blob of mud, golf ball size, covered in AL foil, with IR? Also, how efficient would that be? Is there an IR wavelength that would get absorbed far better than ...
2
votes
2answers
115 views

Coupled ODEs that model a quad rotor

I am working on modeling the vibrations of a quad rotor. The arms that support the rotors are fixed to a center plate; that is, it is pretty much a cantilever beam with an end load. Since this is the ...
1
vote
0answers
63 views

Using aluminium foil as a reflection for UV at 240nm [closed]

Will aluminium foil or sheeting reflect UV light at 240nm being used as a disinfection cell for bacteria in water.
1
vote
2answers
151 views

Moving frames - a blow on “virtual particles”?

There is a polemic about whether virtual particles EXIST, or are only a tool for making our calculi easier. Here is a doubt about their existence, and on the other hand, an argument in support of ...
2
votes
2answers
43 views

Interaction between body and fluid

I'm trying to understand locomotion of bodies in fluids with low Reynolds number and I'm having a hard time to understand the interactions between the body and the fluid. Suppose $D\subset ...
4
votes
1answer
108 views

How do scientists estimate elemental-abundance in the universe?

I understand how cosmological observations can estimate the amount of 'baryonic matter' in the universe, but what I don't understand is how scientists can estimate the abundance of a particular ...
0
votes
0answers
31 views

Free groups and their appearance, emergence and applications in physics

While trying to develop my knowledge of group theory in physics from a more formal point of view, I noticed an entity called a free group. I'm aware that it is extremely important in pure mathematical ...
6
votes
1answer
261 views

What is the Poynting vector of an electron?

On chapter 27 of "The Feynman Lectures on Physics Volume II: Mainly Electromagnetism and Matter", Richard Feynman says: Finally, in order to really convince you that this theory is obviously nuts, ...
3
votes
1answer
152 views

Why does the Cassini probe experience jerky acceleration in deep space?

I was looking at this plot of speed over time for the Cassini probe. What's going on at the right, after mid-2004? Why does it keep slowing down and speeding up again?
5
votes
1answer
129 views

Explanation for “if all accelerated systems are equivalent, then Euclidean geometry cannot hold in all of them”

I'm doing an EPQ (mini college research paper) on gravity, and I found a site that explained things in simple terms. I am having trouble understanding how Einstein came to his revelation space-time ...
1
vote
2answers
156 views

Why are the dineutron and diproton unbound?

It is known that there is no diproton and dineutron nuclei. Does this mean that two protons or neutrons are not actually attracted to each other? Even if the attraction was weak, wouldn't it cause ...
0
votes
2answers
77 views

Why does $\hat n \times (\vec E_1 - \vec E_2) =0 $ imply that the tangential electric field components are equal?

On page 8: http://local.eleceng.uct.ac.za/courses/EEE3055F/lecture_notes/2011_old/eee3055f_Ch4_2up.pdfele I don't understand why $E_{t1} = E_{t2}$ is equivalent to $\hat n \times (\vec E_1 - \vec ...
2
votes
1answer
62 views

Ambiguity in ordering of isospin states for Clebsch-Gordan coefficients

In studying isospin for nuclear physics, I am confused a bit by an ambiguity I found. If a process that goes from $K^- + p \rightarrow \Sigma^0+ \pi^0$, I can write the isospin for the left hand side ...
1
vote
0answers
55 views

Finding the metric [closed]

If given the metric: $$ds^2=e^{2U}(dt+w_idx^i)^2-e^{-2U} d\overrightarrow{x}^2$$ where $w = w_idx^i$ is one form How to find the metric in order to find the inverse metric? The new thing about this ...
0
votes
1answer
47 views

Streamlines for the velocity field $(x, y, 0)$?

Using the equation $$\frac{dx}{x} = \frac{dy}{y}$$ the streamlines for the velocity field $u = (x, y, 0)$ are given by $x = By$ where $B$ is some arbitrary constant. This will give us infinitely ...
-1
votes
2answers
147 views

Why does a photon take less than a week to come out of the convection zone of the sun?

Sun consists of three parts: Radiation zone, Convection zone, Photosphere . When photon is formed at the core, it has high energy equivalent to $\gamma$ ray. When it crosses the radiation zone, it ...
0
votes
1answer
31 views

Rate of work done by fields in a finite volume

In Jackson's Classical Electrodynamics, the rate of work done by fields in a finite volume is defined as $$\int _{v}\vec{J}\cdot\vec{E}\,d^{3}x^{'}$$ How?
3
votes
3answers
164 views

A misunderstanding regarding infinite square well

Here is a picture of the energy states of infinite potential well. We can see That the first level have a half wavelength which fittes with a full wave of the second level. $$\frac{ \lambda _{1} ...
6
votes
3answers
2k views

How do blankets keep you warm?

I heard a famous physicist (was it Feynman?) argue that blankets do not keep you warm by trapping heat but by trapping air next to the body. Is this true?
0
votes
0answers
24 views

Recommendation for contra-variant and contra-variant vectors in the context of special relativity [duplicate]

I have just started studying covariant and contra-variant vectors in special relativity. I am finding difficulty understanding this topic. Can anyone recommend a book (with a detailed chapter) or ...
0
votes
1answer
184 views

Liquid placed in a rotating cylinder

The Question A closed vertical cylinder is filled with an incompressible liquid of mass m completely. The cylinder is now sealed from all sides and rotated about ...
2
votes
0answers
21 views

Is the observable universe growing or shrinking? [duplicate]

For a lack of better word, I used growing and shrinking in the question, but what I really mean is: Are objects that are now in the observable universe passing getting out of range in the future, or ...
1
vote
1answer
329 views

Calculating the moment of inertia in bifilar pendulums

I'm an A2 student, and I've been looking into how experimental and theoretical determined mass moments of inertia differ. I came across a method (search Youtube for Measuring Mass Moment of Inertia - ...
0
votes
1answer
43 views

bimolecular reaction master equation

I was wondering how to write down the deterministic rate equation for a bimolecular reaction with similar particles. e.g. $A \rightarrow^{k_+} B +B$ and $B +B \rightarrow^{k_-} A$ now the rate ...
20
votes
7answers
6k views

Where on Earth does the mass of 1 kg actually produce a 1 kg reading on a digital scale?

Gravity on Earth varies by about 0.1% between poles and equator. If someone was buying/selling something mass critical e.g. gold, where is the standard place on Earth where a 1 kg mass produces a 1 kg ...
1
vote
1answer
58 views

How two prove the second sound velocity is $1/\sqrt{3}$ times than the first sound [closed]

From Landau two hydrodynamics model in superfluid, we have the result $c_1^2=\frac{\partial P}{\partial \rho}|_T$ and $c_2^2=\frac{\rho_s s^2 T}{\rho_n c}$. In the zero temperature limit, how to ...
3
votes
3answers
171 views

How to theoretically define a concrete operation to perform in order to measure the length of an object?

EDIT: Some answerers pointed out that the title of this question is in contrast with what is actually been asked in the body of the question, so I changed the title accordingly. The original title was ...
0
votes
0answers
18 views

How does live load versus dead load effect roof slip-resistance testing?

I have tested a wide variety of roofing materials for slip resistance in a range of roof slopes using various boot outsole materials. With all test protocols, equipment, and conditions being equal, ...
0
votes
0answers
31 views

Thermal conductivity of semiconductors - theoretical function?

Below is a plot of the thermal conductivity coefficient for Gallium Arsenide, reproduced from 3: I would like to interpolate the data, but I don't know what fit function to use. I tried a generic ...
20
votes
1answer
453 views

What are the proposed realizations in the New SI for the kilogram, ampere, kelvin and mole?

The metrology world is currently in the middle of overhauling the definitions of the SI units to reflect the recent technological advances that enable us to get much more precise values for the ...
2
votes
3answers
65 views

Why inversion of wave for rope fixed at one end?

Setup: A rope is fixed at one end to a wall. You swing the other end up and down once. A wave starts travelling. It moves, hits the wall, then flattens, then is created again underneath (inversed), ...
2
votes
0answers
61 views

Question about massive spring and SHM [closed]

A mass $M$ is resting on the end of a spring with constant $K$. The mass of the spring is $m$, and the displacement of each element of the spring is proportional to the distance from the fixed end ...
1
vote
1answer
110 views

Why find the curl in this paper?

I was crossing over this interesting paper http://arxiv.org/abs/hep-th/9404006 when I couldn't realize what happened in the Second Section p. 3: They introduced the metric: $$ds^2 ...
3
votes
1answer
92 views

Darkest matter on Earth (“pure black”)

What is (for a human's eyes) the natural or synthetical matter on Earth (i.e. not in Space) that emits the least quantity of visible photons while being lightened by sunlight? In this matter, how is ...
0
votes
1answer
120 views

Applying Euler Homogenous Function Theorem to $df$ or $f$

I am currently reading Demirel's Nonequilibrium Thermodynamics in order to learn more about entropy and nonequlibrium thermodynamics However I and stumped on how the author's do the following step: ...
0
votes
0answers
95 views

How to find force acting on ferromagnetic material when it is placed in external magnetic field?

When we bring magnet towards ferromagnetic material ( like iron nails), then material gets attracted towards magnet. Since there is motion of material, there must be force acting on it. How to find ...
0
votes
1answer
31 views

Relation between Curie temperature and exchange interaction's constant $J_\text{ex}$

I'm running a Monte Carlo simulation on a generic magnetic nanotube. In my results, I found out that the relation between the Curie temperature (that is, the temperature by which a ferromagnetic ...
1
vote
2answers
63 views

Mass of NGC 1097 Galaxy

I've been looking all over the internet for this and can't seem to find a reference. Can anyone refer me to a paper citing the mass of NGC 1097 based on luminosity?
0
votes
0answers
82 views

Advantage and disadvantage of weak field approximation

Many textbooks related with GR, covers weak field approximation, (also called Linearized gravity). Since so far, i have been calculated many this with this $i.e$ $g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu}$ ...
1
vote
0answers
63 views

Frequency of flute note heard using Doppler effect when both the source and observer are moving

Let us consider this scenario. A bicycle rider and a flute player are moving in the same direction at speeds 36 km/h and 18 km/h. The flute is producing a note of frequency 600 Hz. We need to find ...
1
vote
1answer
82 views

What will I see if I travelled to a distant planet in 100 times faster than speed of light and look back? [closed]

Consider this scenario. I enter a space ship at 10:00 AM, it starts to move at a speed 100 times faster than light, I travel for 55 mins. And then slow down to very much less than speed of light and ...
1
vote
1answer
51 views

Is getting the ground state of Edwards-Anderson model NP hard?

I know 1D and 2D Ising model has a general solution. And I also know getting the ground state of 2D Ising model with transverse field and 3D Ising model is NP-hard.[Onsager][Barahona] So my question ...
6
votes
1answer
696 views

Movie Interstellar - Question about Escape Velocity

The movie Interstellar shows people on a water planet where time is dilated so much that 1 hour is equal to 7 years back on Earth. Even though they lift off from Earth using a Saturn-V two stage ...
10
votes
2answers
128 views

Is quantum uncertainty a function of how matter is distributed in the universe?

As an outcome of his PhD thesis work, Richard Feynman and John Wheeler wrote a series of papers on how the kickback on an electron as it emits a photon can be modeled accurately as the result of an ...
0
votes
1answer
45 views

What happens to K.E. in matter antimatter annihilation?

If I have two matter and antimatter particles, say an electron and a positron, each moving towards each other with a certain speed, they annihilate after the collision. Does the energy of the photons ...
0
votes
0answers
47 views

Can we use combined symmetry to simplify the calculation of algebraic PSGs?

In classifying mean-field spin liquids under projective construction, the algebraic projective symmetry group (PSG) approach focus on the mathematical construction of the possible extensions of the ...
0
votes
0answers
65 views

Reason behind formation of doublets in diffraction spectrum

like if you see is Sodium (and also in Mercury), there are two discrete lines of Yellow color.. What's the reason behind formation of doublets?
0
votes
2answers
366 views

Accurate way to measure angular spread of a laser beam

While doing an experiment to measure the angular spread (or say divergence) of a beam of laser (which in my case was an inexpensive diode laser), what is the most accurate way of measuring the ...
1
vote
1answer
54 views

Most general second-rank symmetric tensor in Einstein theory

I am reading MTW page 407, Exercise 17.1. (a) Show that the most general second-rank, symmetric tensor constructable from Riemann and $g$, and linear in Riemann, is $$a R_{\alpha\beta} + b R ...

15 30 50 per page