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General Science / What is the process of hurricanes creation?

« on: 25/10/2019 01:21:04 »

I have read about the warm sea as the driving force for the hurricanes, and the Coriolis acceleration as the reason for its rotation. But I could not find a logical connection for the event as a whole. I will try below an explanation step by step, and would like to know if it makes sense, or where I can find a better one:

1) In regions of shallow waters and near the tropic parallels (Gulf of Mexico for example), the sun light is maximum in the summer. Because the sea is shallow, it warms more than the ocean nearby.

2) A lot of water evaporates from that warmed sea, and the added molecules force a displacement of the existing ones in all directions.

3) As the air pressure is lower above than sideways, most of the expansion is upwards.

4) The equilibrium outcome is a huge volume of warm air above the sea, if there are not winds to dissipate and disturb that state.

5) When the summer finishes, the sun light (the actual driving force for the expansion) in the same region weakens.

6) All that volume of air loses some temperature and its pressure drops as a consequence.

7) Air from outside moves to that region, due to the pressure difference.

Due to the Coriolis acceleration the radial winds deflect sideways

9) An hurricane is formed.

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Plant Sciences, Zoology & Evolution / Why so many flowers have 5-fold simmetry?

« on: 06/12/2018 14:22:58 »

Of couse there are also examples of 3-fold, but 5 seems to me the most common type. I wonder if it is related to some orbital angle in relevant molecules. But searching the web, I found typical angles of 109.5, 120 or 180 for organic molecules. Nothing that can explain 5-fold simmetry. 

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Technology / How can a lamp delay result from a loss of phase?

« on: 25/08/2018 23:32:30 »

I was at a rented beach house last week when one of the phases collapsed. The system has 2 phases, one for everything but the electric shower, the other for the shower. Because I am still waiting for the energy supplier to fix the problem, I had to change the wiring in the electric distribution board and put all the house in the "good" phase.

All the house except for the (110 V) air conditioner, that has its own circuit breaker and get the "bad" phase direct from the electric meter. Measuring the Voltage, there are less than 70 V available for the air conditioner.

However, if I insert an light bulb in that power plug, it glows after some delay, and the voltage increases to about 100 V (

And if I plug the air conditioner in parallel, it works!

I wonder if there are loose wires in the transformer that reduces the tension from the city line to the house, and the delay results from an electromagnetic force joining them, when the current flows though the lamp, like a kind of relay.

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Physics, Astronomy & Cosmology / What is best QM description for electromagnetic scattering?

« on: 18/07/2018 03:35:29 »

One of the methods to know the crystalline structure of materials is the X-ray diffration. The periodic array of atoms make possible that the scatering of an incoming electromagnetic wave be in phase for some angles of the directions source-sample and sample-detector.

My doubt is how to describe what happens when the incoming wave reaches one atom. In some texts, the eletrons vibrate according to the wave frequency, and being an accelerated charge, send a new (scattered) wave, in phase with the original and in the same frequency.

But the quantum description of the event is the absortion of a photon by the atom and further release of another one.

According to the first (classical) description, a spherical wave spreads from the moving electron. Because the inter-atomic distances are much smaller than the distance  sample-detector, the later records basically plane waves with the same direction. 

But according to the QM explanation, the photon released by the atom, after returning from the excited state, has some direction, and only by coincidence is the direction sample-detector.

Or I can say that the wave function of this photon is a spherical one, a superposition of infinite plane wave vectors in all directions? And when a photon is detected, its wave function collapses to that direction sample-detector.

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Chemistry / Can electrons in a crystal have the same quantum state?

« on: 19/06/2018 13:13:50 »

It is clear to me that 2 electrons can not ocuppy the same quantum state in an atom. But what about larger systems?

1) In a small crystal of copper, can electrons of the first energy level of different atoms, each bounded to its nucleus, have the same quantum state (energy, angular momentum, spin). Or is it only required for "free" electrons of the last orbital layer?

2) A coil of polycrystalline copper wire of 100m lenght can also be considered a quantum system, no two of its electrons having the same state?

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Physics, Astronomy & Cosmology / What is MCRF?

« on: 09/05/2018 23:21:52 »

I am trying to understand the so called “momentary commoving reference frame” (MCRF) used for the energy-moment tensor in GR.
Using the example of the suspension system of a car, each cubic element around a point of the spring has a stress tensor changing with time, as the car moves trough an off road way. The elements have different velocities because they vibrate due to the loads and elastic constant of the spring. Velocity * spring density = p (momentum per volume). p_x, σ_xx,σ_yx and σ_zx form one of the lines of the 4x4 energy-moment tensor.   
The importance of p and tensions in elasticity relates to the equation: F_x = ∂σ_xx/∂x + ∂σ_yx/∂y + ∂σ_zx/∂z, where Fx = ∂p_x/∂t.
Similar for the other axis.
It is not required that the elements are momentarily at rest to that analysis.
I assume that MCRF is necessary in relativity because different speeds would require Lorentz transformation between the elements, and it must be avoided.

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Physics, Astronomy & Cosmology / What breaks the symmetry in this thought time dilation experiment?

« on: 04/05/2018 23:23:14 »

A spaceship passes close enough to the earth to check the clocks here. Its speed is 0.8c, but just when the distance to here is minimum, the engine is turned on in order to decelerate it. It is regulated to keep an constant artificial gravity = g in the ship, not only until it stops, but until it is back to earth at 0.8c to the opposite direction.

According to the equations for relativistic uniform acceleration, and setting c = 1 light second/second, and g = 9.8/(3*10⁸)ls/s²:

τ = 2*atan(v)/g = 389,2 days according to the ship clock.
t = 2*sinh(gτ/2)/g = 472,4 days according to the earth clock.

The situation is pretty symmetric. Both earth and ship can measure an acceleration = g at its own frame of reference all the time. Both have the same right to say: I am at rest.

What breaks the symmetry, if the principle of equivalence doesn't allow to differentiate between acceleration and gravity?

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Physics, Astronomy & Cosmology / How to explain the kitchen balance paradox?

« on: 16/04/2018 21:40:57 »

I was puzzled for a while, and then found an explanation, but it is tricky at a first sight.

Using the Newton's equation: a_s = GM_s / r² for the  gravity acceleration of a body by the Sun, and replacing the constants by its values, here at Earth, a_s is 0,006 m/s².

As g (only due to Earth) is 9.8  m/s², that means that at midnight it is a net 9.806 m/s², because any body is being pulled by Sun and the center of the Earth.  At noon, the effect of the Sun is opposite and it is a net 9,794 m/s².

That effect could be detected by a kitchen balance, because the difference (9.806 - 9,794 ) / 9.8 = 0,12% is not so small. An object of 3000 g would show at least 3g of difference.

But there is no difference at all. Why?

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Physics, Astronomy & Cosmology / Was an exponential universal expansion ever postulated?

« on: 21/03/2018 01:14:08 »

I was watching a video about astronomy and from the Hubble Law ( v = H0*r ), the age of the universe was said to be 1/H0. The estimated age changed in the last decades acccording to more and more precise measurements of H0.

At first it puzzled me, because v = H0*r is a differential equation, dr/dt = H0*r => r = Aexp(H0*t). But the age of the universe would be much greater, and not 1/H0.

After some time I realized that physics since Hubble time may have taken the galaxies as moving bodies free from external forces => constant velocities, and t = d/v. So, going backwards, in a time t = 1/H0 all the stuff was in a single place. And H0 as measured now, because it had to be greater and greater in the past.

When Hubble and others looked at so nice linear relation between a function and its derivative, an exponential universal expansion should be a natural hypotesis. But I never read that it was considered.

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Physics, Astronomy & Cosmology / Is this calculation of simultaneity right?

« on: 31/01/2018 00:13:07 »

Suppose there is an atom clock in alpha centauri, syncronized to the earth. An observer there could detect now, signals sent from here in jan 2014, considering 4 light years of distance.

A spaceship coming from earth at 0.5c, crosses alpha centauri when the clock at the star shows jan 2018. The corresponding time at earth for the ship is t' = t - vx = t - 0,5 * 4 = jan 2016. An observer in the ship could detect signals sent from here in jan 2012.

A spaceship with the opposite velocity, flying to earth at 0.5c, crosses alpha centauri also when the clock at the star shows jan 2018. The corresponding time at earth for the ship is t' = t + vx = t + 0,5 * 4 = jan 2020. An observer in the ship could detect signals sent from here in jan 2016.

If it is right, there is any intuitive way to realize how that gap of 4 years between the available signals for the ships should happen?  I am always unconsciouly dealing with light speed as a normal material speed, instead of a constant, when I try an intuitive explanation.

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Physics, Astronomy & Cosmology / Is a space time curvature possible without mass?

« on: 16/01/2018 19:16:55 »

When deriving the Schwartchild solution, the Einstein tensor is equal to zero. By spherical simmetry considerations, after calculating all Christoffel symbols, we get the metric, where the g₀₀ and g₁₁ have a constant divided by r. If we require that the Newton gravity law must be valid for low velocities, that constant is GM. And it is interpreted as a point mass in the center, or a spherical simmetrical distribution of mass. In the later case, the metric is valid only outside the body.

I wonder if we allowed regions of spacetime have Schwartchild metrics without requiring Newton law for low speeds. And keep an arbitrary constant there, not putting a mass to explain the field.

After billions of years, dust from the surroudings would not "fill the voids" with mass?

And couldn't an intelligent man, after inventing calculus, looking at that bodies, conclude that mass is the cause of an attraction force that explain the planets orbits? When it was really a consequence of the metric?
 
We could raise an objection about why a metric like that, instead of a Minkowski one. But it is like asking why everything is moving, instead of at rest, or why Being, instead of Nothing.

The reason of that idea is the fact that for vacuum solutions the energy-moment tensor is zero, and mass is not required to calculate the metric.

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Physics, Astronomy & Cosmology / How can the field equation be zero while the Ricci tensor is not?

« on: 28/10/2017 19:54:00 »

In the so called vacuum solutions, the Einstein tensor G^μν = R^μν  - 1/2*g^μν*R = 0. I saw a proof that the former equation implies in R = 0 and R^μν = 0. It follows from multiplying by g_μν, given R - 1/2*4*R = 0.

But when deriving the Schwarzschild solution, after calculating the Ricci tensor (R^μν) and the Ricci scalar (R), from the spherical symmetries of the problem, both are non zero. And the equation R^μν  - 1/2*g^μν*R = 0 is used anyway to derive 4 differential equations that eventually result in the Schwarzschild metric.

How is it possible that the field equation are zero while R^μν and R are non zero?

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Physics, Astronomy & Cosmology / Are spiral galaxies expanding?

« on: 16/07/2017 00:41:42 »

If an astronaut can see celestial bodies nearby, it is easy to know if he (she) is rotating or not, as shown in a scene of the film "Gravity". If there is no way to see outside, one way I can imagine is holding some object through a rope. If there is some rotation the rope will show some tension, while winding. That means: it would go away if released.

In this case, I suppose the gravitational field generated by the astronaut is negligible. If the case of a fantastic massive astronaut, it would be necessary to compensate for the gravitational field. If I could feel the object touch me after some time, without tension in the rope, I could conclude that the my gravitational field was strong enough to hold the object. But I would be not sure if was  rotating or not. On the other hand, if the rope kept tensioned, I could conclude that I was rotating, and the object would escape if I loose the grip.
 
If the star velocities at several distances from the center of a spiral galaxy are greater than expected for a steady state, based on its mass density, couldn't that galaxies be expanding? That means, they would come from huge rotating bodies, from which parts were being detached above the escape velocity. Wouldn't be a big coincidence if the spinning velocities were just the necessary to hold the system in equilibrium, not expanding or colapsing?

It is true that it is exactly the case of our solar system, but maybe we are extrapolating that stability to the spiral galaxies, and they are not as a rule, in a steady state.

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Physics, Astronomy & Cosmology / How is the spacetime curvature approximated?

« on: 06/06/2017 01:10:57 »

The classical gravitation law can, at the surface of a spherical homogeneous body, be written as:
a = G*(4/3*π*r³)*μ / r² =  4/3*π*G*μ*r; and the divergence of the acceleration in spherical coordinates is: div a = 4*π*G*μ.
where μ is the body density and G the gravitational constant.
That divergence has units of 1/T². When comparing to the Gaussian expression for the curvature of the surface of the sphere: 1/R²,  there is a similarity. Is it only a coincidence or the GR measure of spacetime curvature for that geometry can be approximated, for small velocities and mass densities, by that expression?

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Physics, Astronomy & Cosmology / Is relativity only necessary to extend the concept to high speeds?

« on: 03/03/2017 20:35:55 »

I found an explanation for the e=mc2 equation at this address: http://www.adamauton.com/warp/emc2.html

Basicaly, it is a thought experiment where one photon is emmitted from one side to the other side of a box at rest. By moment conservation, the box is shifted to the other side and stops moving when the photon finishes its journey. As the final position is different from the initial position, but the center of mass should be invariant (no external forces), some "mass" was removed from one side and placed in to the other one. The equations gets E=mc2. It is assumed low speeds.

The equation uses only that light has momentum. So, even while it is explained there that the famous formula comes from special relativity, there is nothing of relativity in the deduction.

Question: Is relativity only necessary to extend the concept to high speeds? 

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New Theories / Air is blue and space is CMB

« on: 27/01/2017 22:48:37 »

1) While we used to say that sky is blue, and Gagarin said that the earth is blue, it seems more correct to say: air is blue.

2) When we see a mountain not too far the green of vegetation or the ochre of the soil are evident. Far away mountains are bluish.

3) Radio telescopes can see the color of the space, that is CMB.

4) Distant galaxies are reddish.

5) Photons from distant galaxies are scattered by cosmic powder of different materials and sizes, lowering its wavelength

6) That scattering, considering the reflexion in all directions, also results in the CMB color.

7) It is not necessary to assume the expansion of the universe to explain either the CMR or redshift of galaxies.

By  Occam's razor the expansion of the universe is not necessary, while it is a possible explanation, as the hypothesis of creation by God.

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Technology / What are these pieces of apparatus comprising a series of electrical coils?

« on: 24/01/2017 22:23:14 »

A school is running out of business near my home. They are selling a lot of stuff, among them this electronic devices with 2 coils and 3 terminals (photo in annex) that I got.
I measured in one of them 150 Ohms between the extreme terminals and 75 Ohms between the middle one and the others. It is written 2x1800 0.3A. For the other one the figures were 14500 and 7250 Ohms. And it is written 2x18000 0.03A.
Moving a magnet through the squared hole it is possible to measure a voltage between terminals, but I suppose they were no designed only to show that to the students.

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Physics, Astronomy & Cosmology / Why a gyroscope stops precessing before falling?

« on: 28/07/2016 02:17:08 »

I bought a gyroscopic toy, and realized that it can start precessing badly (I put it inclined on the ground), but before fall, it gets still, completely vertical for a while.
I always thought that it would precessing more and more until the RPM become too low and it fall.
Why does it happen?

link:https://youtu.be/UZYlW6ErqdI

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Physics, Astronomy & Cosmology / What is the basis of the twin paradox and general relativity?

« on: 20/06/2016 01:50:32 »

I have found the question below in an old thread about the twin paradox. I could not get an answer at that thread or from other sources. The problem for me is: if the situation is totally simmetric, both twins return at the same age. But isn't it against SR theory?
I assume that all acelerations and desacelarations are the same for both the traveller twins, so GR should not explain any difference.

Things get interestinger when you have triplets, one stays on the ground, one goes off in a spacecraft to the celestial north, the other off to the celestial south, and both later return. What are their relative ages, and why?

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Technology / Sea waves high speed

« on: 27/04/2016 23:51:53 »

This month, part of a new bike path in Rio de Janeiro was destroyed by the upward force of strong sea waves.
The lane is parallel to a road along a rocky shore, and at 50m above sea level, and can be modelled as a collection of beams, being supported by pillars.
It was designed to support its own weight, bycicles and people, all downward forces. The water simply pushed it upward disconnecting it from the pillars.
Of course there is no 50m high waves here. The waves crushed the inclined rock wall, and were reflected upward.

If the water could reach 50m, mgh = 1/2mv² means a speed about 30m/s or 100km/h.
Is it right? I have never known that the impact of waves on shores could reach such a high speed.