2
votes
2answers
51 views

Why are racing catamarans' hulls not teardrop shaped?

Looking at the America's Cup 72 class catamarans, I was wondering about their hull shape, which has a sharp wave piercing bow. My question is: since an airfoil shape experiences less drag than a sharp ...
0
votes
0answers
18 views

how much heat will be produced when air is compressed to liquid air [on hold]

I understand about 700 litres of ambient air becomes 1 litre of liquid air. I want to know how much heat will be dissipated when this happens. I appreciate any help.
2
votes
0answers
22 views

Why would an alpha-beryllium neutron source generating a radioisotope not produce controllable net power?

I have a question. I was looking through the table of nuclides and noticed that the energy needed to produce certain radioisotopes was less than the energy given off by the radioactive decay of that ...
1
vote
1answer
35 views

Is it theoretically possible to prevent or deter a star from becoming a black hole?

Suppose NASA decides too many black holes are being produced in a year, so it decides to do something about that. Given our current scientific knowledge, is there theoretically any way NASA could ...
0
votes
0answers
16 views

Why do high altitudes have larger diurnal temperature variation than lower altitudes?

It seems like the lack of atmosphere should not be playing a role in the diurnal temperature variation because that's what makes it colder. Mountains are not that dry, usually.
1
vote
1answer
21 views

Why does moving the source-slit closer to the double-slit plane decrease the sharpness of the interference-pattern?

Thomas Young used a single-slit plane before the two-slits plane in order to make the light source coherent. My book (NCERT Physics II) presents the above query and writes: Let $s$ be the size ...
0
votes
5answers
115 views

Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure ...
0
votes
1answer
35 views

Does Schwarzschild metric have cosmological horizon?

Since the space is not expanding in the Schwarzschild metric does that mean that there is no cosmological horizon? Also, what if the Schwarzschild metric was not asymptotically flat and we replace ...
43
votes
1answer
2k views

Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some ...
4
votes
2answers
63 views

Do individual rays of light lose energy via the inverse square law?

We've all heard of the inverse square law, but apparently that refers to the flux or intensity or number of photons hitting an imaginary surface area. This is not exactly what I want to ask about. ...
-1
votes
1answer
32 views

compton's formula for change in wavelength

I want to measure the shift in wavelength predicted by Compton's formula. I find that I cant measure a shift of less than 5% and that I also cannot measure at angles greater than 150 degrees. What is ...
-2
votes
0answers
26 views

gravity and inflation

Looking at the interaction between mass and the higgs field. Could gravity be a result of the topographical distortion of the fabric of space-time as the universe accelerates under inflationary ...
2
votes
2answers
24 views

Galvanic Cells and Electric Potential

In a battery or a galvanic cell, the electric potential of the battery is due to a difference of charges between the two cells like in a capacitor? So it is the electric field due to this separation ...
2
votes
1answer
23 views

how can $\frac{kqq_o}{r}$ be $U$ for both a particle and a system of two particles?

If there is a charge $q$, at a distance $r$ from it there is a voltage and the potential energy of a test charge $q_o$ would be $\frac{kqq_o}{r}$. Now if I construct a system of two charges a ...
2
votes
0answers
34 views

interpreting the dirichlet-principle

In obstacle problems (see e.g. wikipedia here) we are minimizing the dirichlet energy $$ I[u]=\int_D\|\nabla u\|^2dx\tag{1} $$ The Dirichlet-principle states that minimizing $I[u]$ is equivalent to to ...
0
votes
1answer
46 views

How to prove that sum converges to integral using density of states?

Essentially, I would like to prove $$ \sum_k f(k) \to \int f(k) \rho dE \tag{1}$$ where $$ \rho = \frac{dk}{dE} \tag{2}$$ is the density of states and $k \to \infty$. The model is that there is a ...
4
votes
1answer
60 views

Would neutronium emit heat?

Since accelerating a charge creates EM radiation, and there are no charges in neutrons to be accelerated, would that mean neutronium emits no radiation? Consequently, to preserve the second law of ...
1
vote
0answers
19 views

Is there a well defined way to shift Cauchy surfaces back and forth?

Let $S$ be a Cauchy surface on a four-dimensional connected Lorentzian manifold. Define $\Gamma(S)=\{\gamma:\mathbb{R}\to M\mid \gamma(0)\in S, \gamma$ is a unit speed geodesic passing orthogonally ...
0
votes
1answer
54 views

How small would an electron have to be in order to become a black hole?

According to quantum mechanics electrons don't behave like everyday objects. Would this prevent the formation of a black hole? If so why? Also, assuming they behave like everyday objects, at what ...
0
votes
0answers
54 views

Conceptual questions on the path integral formulation of QFT

I'm currently trying to teach myself the path integral formulation of QFT (having studied the canonical approach previously), but I'm having some conceptual difficulties that I hope I can clear up ...
0
votes
1answer
7 views

Quasi-fermi levels in a solar cell?

I was wondering, if my fermi levels splits up due to n and p type doping into two fermi levels, one for the p type one for the n type, and now due to light radiation my fermi levels split up into 2 ...
4
votes
1answer
24 views

Why exactly do sometimes universal covers, and sometimes central extensions feature in the application of a symmetry group to quantum physics?

There seem to be two different things one must consider when representing a symmetry group in quantum mechanics: The universal cover: For instance, when representing the rotation group ...
-3
votes
0answers
28 views

Can atoms exist [duplicate]

Can an atom be created from 2 top and one bottom quark together with a tau selectron? How would its properties differ from a hydrogen atom? What combinations of quarks and selectrons are possible to ...
2
votes
2answers
72 views

Can atoms with top / bottom quarks exist?

Do we have examples in nature or the lab of atoms constructed of 2 top and 1 bottom quark and a tau selectron? How would its properties differ from a hydrogen atom?
1
vote
0answers
650 views

Squaring a Vector? [migrated]

So this one is basic. And should be pretty quick. Lets say that I have a vector $\vec{r}$: $\vec{r} = \vec{x} + \vec{y} + \vec{z}$ Is this true: $\vec{r}^{2} = \vec{x}^{2} + \vec{y}^{2} + ...
2
votes
1answer
59 views

How can we obtain equations of motion from $\iota_{X_{H}}\omega =dH$?

I don't know if this is an obvious result and I am just missing a trick, so please forgive me, but how do we obtain equations of motion from the following equation. \begin{equation} \iota ...
0
votes
1answer
38 views

Allowed Virtual Displacements

I am having trouble understanding the kinds of virtual displacements which are permitted for a given constrained system. I have a specific example in mind: A block of wood resting on a table parallel ...
0
votes
1answer
30 views

Does motion with constant proper acceleration, in a flat region, necessarily mean straight hyperbolic motion?

Is motion of a participant with constant proper acceleration, in a flat region, necessarily straight, hyperbolic motion (with respect to members of any inertial system, in that region)? Or is for ...
-1
votes
0answers
12 views

Plane color shift

Please explain this phenomenon. In google earth, type in these coordinates: 26.07712027, -80.17626934 This is I'm assuming captured by some sort of radar, and this shifts the color spectrum in motion ...
1
vote
2answers
45 views

Why do so many galaxies in clusters have a near zero velocity?

I'm looking at a velocity chart of the Coma Cluster: And the question occurred to me: why are there so many galaxies that have a zero velocity (relative to the core of the Coma Cluster which is ...
-1
votes
1answer
29 views

Lifting a block or sliding a block- Which will consume more energy?

A box with mass m units resting on a table with smooth surface (slightly oily). A to B : d units Action 1 : Slide the box from Point A to B. Action 2 : Lift the box from A to B in an arc fashion. ...
0
votes
3answers
49 views

Regarding synchronization of clocks in special relativity

I am trying to read of synchronization of two clocks in same inertial frame in special relativity. Suppose we have two synchronized clocks in an inertial frame placed at positions $x_1$ and $x_2$ in ...
3
votes
2answers
393 views

Two Point Universe

Imagine a universe consisting of only two point masses, neither of which are in motion. Would they be drawn towards each other? Does there need to be motion for the curvature of spacetime to affect ...
0
votes
2answers
45 views

When a neutron star accumulates enough mass, does a black hole start at its center?

With less dense bodies, such as the earth and the sun, the center has less gravity/density (since there's an equal amount of mass surrounding the center, pulling out on it from all directions). Does ...
2
votes
1answer
34 views

Complex / real representations of the Lorentz group

In Michele Maggiore's book "A Modern Introduction to QFT" he describes the spinorial representations of the Lorentz group as The representations are in general complex. I always thought the ...
2
votes
0answers
62 views

Polarization Sums in QCD

In the case of a Spin 1 massive particle it's possible to demonstrate that $$\sum_{\lambda=0,\pm1}\epsilon_{\lambda}^{* \ \mu}\epsilon_{\lambda}^{\nu}=-g_{\mu\nu}+\frac{q^\mu q^\nu}{q^2}$$ for a ...
1
vote
0answers
20 views

Are there any concrete data on the period of large amplitudes? To what extent are correction formulas useful?

Is there a site/pdf where I can find results of real and accurate experiments concerning the period of pendulums from 0 to 90°? (actual periods and not formulas). I once found one, but in spite of ...
-2
votes
0answers
11 views

Bandlike vs. Excitonic Semiconductors

What is the different between 'bandlike' semiconductors and 'excitonic' semiconductors and how does this relate to whether they are organic or inorganic? I also wonder how such bandlike or excitonic ...
1
vote
0answers
16 views

Hypermultiplet as BPS particles

In the third paragraph of page 7 of the paper arxiv:1112.3984 it mentions that we form a basis out of hypermultiplets on the charge lattice $\Gamma$. My questions are: In what sense do we form such ...
-1
votes
0answers
34 views

Final temperature of water+ice+water Mix [on hold]

I found this physics question: In a container there is a mixture of water at $ T = 0°C$, mass $m_w = 300g$, and ice, mass $m_i = 600g$. More water is added into the container, mass $m = 1100g$ at ...
0
votes
2answers
27 views

Would a magnetic needle standing on it's point on a magnet be more stable than the same needle stood on a non-magnetic surface?

So I was watching MinutePhysics' video 'How long can you balance a pencil?' and it turned out to not be for very long. Would introducing a magnet to the equation make for different results? We can ...
-1
votes
0answers
31 views

Why do electrical charges given to a conductor come to the surface? [duplicate]

It is said that any charge given to a conductor comes to its surface. Should all the protons come to the surface? Should all the electrons come to the surface, or should all the free electrons come ...
2
votes
2answers
81 views

Could a civilisation contact us by laser from 50 light years away?

The Kepler Space Mission has discovered over 1,000 planets. These discoveries may increase the confidence of some people that other civilisations exist. That is an opinion issue, and not what I want ...
0
votes
0answers
32 views

Is this the reason why a circuit with no components (except wire) would discharge the battery faster?

I read that if I simply connect two ends of a battery it would discharge really quick and it would last longer if the circuit contained e.g. a light bulb. I wondered why is this happening and my ...
0
votes
0answers
33 views

Reason for strange magnetic ball movement

I was playing with a set of those neodymium magnet spheres and noticed a couple of strange behaviors (which I believe are related so I'm only positing a single question) and I was hoping to get an ...
0
votes
1answer
34 views

Can capilliary action move liquid against gravity?

I was wondering if it was at all possible to very slowly suck up water from a cup with a rope, and then deposit the water into another cup on a 3cm thick book or similar object. Here is an example ...
6
votes
2answers
186 views

Shaken vs stirred, is there a difference? [on hold]

I was looking up tequila Drink recipes for the up coming holiday, and I kept seeing ones calling to be shook and other to be stirred. So I wondered: is there really a difference? does stirring provide ...
0
votes
1answer
23 views

Body that both cools (proportionally to temperature difference) and heats with constant power

This is almost more of a math question, and a simple one, but I can't figure it out, and I haven't been able to find a solution online since I don't really know what words to search for. There is a ...
-3
votes
0answers
59 views

Why photon have zero rest mass?

If photon have zero rest mass then the term E=hf should also be zero because if rest mass is zero then relativistic mass is also zero and so on by Einstein mass energy relation energy shoud be zero ...
0
votes
1answer
40 views

Data on Nuclear Fusion [on hold]

I'm currently doing a detailed project on Nuclear fusion and it's future. I've found some great books on the subject so thats not a problem. What i'm struggling to find is data more specifically ...

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