All Questions

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 ...
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.
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 ...
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 ...
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.
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 ...
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 ...
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 ...
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 ...
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. ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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?
650 views

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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...