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

« on: 01/09/2018 00:05:04 »

However, as metals heat up, the resistance increases, and more of the voltage drop will occur across the lamp, causing it to heat up even more, and eventually to glow visibly. But it won't reach full voltage/full brightness, as it is still in series with some other load.

But the increase of the resistance with temperature doesn't explain the fact that the final voltage: 100V was bigger than the open circuit voltage: 70V. 

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

« on: 31/08/2018 11:13:19 »

A lamp needs some time to heat up. Normally that delay isn't noticeable, but if the voltage is low it will take longer than usual.

But here the time delay was too big, and moreover the voltage at first dropped after tunrnig the switch on. After some time the lamp shined and the voltage increased above what it was when the switch was off.

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

« on: 31/08/2018 11:05:58 »

If the voltage varied as other appliances turned on and off, it might have been a fault in the neutral connection?

in the days before before the company come, I connected all house in the "good" phase, and everything worked fine, so I don´t think there was a problem in the neutral.. I checked also the continuity between neutrals in the plugs and didn't find anyone disconnected from the electric distribution board,

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

« on: 30/08/2018 19:42:21 »

The guys from the electric supplier company finally came today and fixed the problem. I was not there, but according to my wife they blamed the "sea air" for a bad contact somewhere from the aerial cables out of the house before the meter.

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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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Physics, Astronomy & Cosmology / Re: How is it possible for the Sun to set in the northwest?

« on: 27/06/2018 00:43:18 »

At even higher latitudes the sun doesn't set in the summer.

If we travel to the south, from a place where the midnight sun happens, we will cross regions where the sun at midnight is just below the horizon, exactly to the north.

And it crosses the horizon, in the sunset, between west and north.

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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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New Theories / Re: Re: Critique of scientific method and will we ever find a theory of everything?

« on: 20/05/2018 16:44:40 »

Could this be one of the rare mysteries where philosophy could provide the answer?

If we compare scientific theories to organisms, mutations can happen by several reasons, and what we call philosophy  are a source of them. But most of the mutations are failures. The role of natural selection is played by maths and experiments. Some mutations succeed and theories change.

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Physics, Astronomy & Cosmology / Re: Need help with math problem

« on: 20/05/2018 16:03:06 »

No big deal until the last simplification, when a big luck let the remaining terms, after adding and subtracting to complete (b - a)³, happen to form  3a(b - a )².

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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 / Re: What breaks the symmetry in this thought time dilation experiment?

« on: 07/05/2018 00:36:40 »

It is common to say that the equivalence principle holds locally, for example inside a spaceship, because the tidal forces are too small. But I understand that locally also means small time interval, otherwise time dilation can show the difference as in the example.

Another point is: the ship has a more intense gravitational field compared to the earth’s one, in the meaning of same “g” but greater escape velocity and time dilation. And the associated spacetime is flat, while it is curved for the earth’s one. So, spacetime curvature is not a reliable indicator for the intensity of a gravitational field.

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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 / Re: Who claimed that gravity is a curvature in spacetime?

« on: 26/04/2018 23:30:08 »

Quote from: saspinski

    The difference of gravity acceleration on the Jupiter surface (if it were possible be at rest there), in a given vertical lenght, is smaller than on the Earth surface:

    da = GM/R² - GM/(R+d)². For d =1km, I have found a difference of 0,003 m/s² for Earth and 0,0007 m/s² for Jupiter.

Ae you now merely trying to find ways to make it different, Those are wrong  y the way. See my page on tidal forces.
Jupiter's tidal forces are significantly greater

No. It is right. It is the definition of tidal force, at least for weak fields. Another example is our ocean tides. The effect of the Moon is about twice that of the Sun. And the Sun’s gravitational field (gravity acceleration) is much greater here than the Moon’s one.

quote author=saspinski]
...but why to use GR concepts for something that is in the range of SR?

Wrong. And you made no effort to support such an inalid claim. Why is that?[/quote]

It is well known that SR can deal with uniformly accelerated frames of reference, see Rindler coordinates.

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Physics, Astronomy & Cosmology / Re: Who claimed that gravity is a curvature in spacetime?

« on: 26/04/2018 02:04:13 »

So the idea that the greater the mass the greater the curvature, and stronger the gravity field is certainly wrong. 

I can't see how you got that idea. The greater the mass the greater the gravitational field and tidal forces (aka spacetime curvature) Ohanian's text shows the relationship between the two.

I haven't written it clearly.     
The greater the mass the greater the gravitational field, OK. But not necessarly greater the tidal forces (curvature). The difference of gravity acceleration on the Jupiter surface (if it were possible be at rest there), in a given vertical lenght, is smaller than on the Earth surface:

da = GM/R² - GM/(R+d)². For d =1km, I have found a difference of 0,003 m/s² for Earth and 0,0007 m/s² for Jupiter.

The gravitational field is defined by the Christoffel symbols, no the tidal force tensor.

It is a matter of definition, but why to use GR concepts for something that is in the range of SR?

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Physics, Astronomy & Cosmology / Re: Who claimed that gravity is a curvature in spacetime?

« on: 25/04/2018 02:08:40 »

There is that tradicional picture of a sphere deforming a membrane as a representation of a gravitational field. It can spread some confusion if people take the curvature of this scalar field as a measure of its intensity. And by intensity I mean the fact that the same object would weight more in Jupiter than in the Earth.

As Jupiter is less dense, that curvature would be smaller on its surface.

So the idea that the greater the mass the greater the curvature, and stronger the gravity field is certainly wrong. 

But it is not wrong to say that the curvature of the metric tensor field, defined by the Riemann tensor, is related to its intensity. But intensity here meaning the tidal forces, because they are the same for an observer at rest in the planet, or in free falling, and more apropriate to a description of gravity following the relativity principle.

Using this criteria, a man free falling from a rocket in uniform acceleration would agree with the rest of the crew that there is no gravitational field, because there is no tidal forces.
 

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Physics, Astronomy & Cosmology / Re: Who claimed that gravity is a curvature in spacetime?

« on: 22/04/2018 22:39:27 »

You did get lost. Its not possible to have a non-zero Riemann tensor for a uniform gravitational field. Its actually the definition of a uniform field.

Yes, I changed a γ by a δ of one of the Γ's. There are a lot of them. But now I checked everyone, and all components are really zero.

So, in the specific case of an uniform gravitational field, the spacetime is flat for any observer (being or not in free fall).

For conventional (non uniform) gravitational fields, the spacetime is curved for any observer.

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Physics, Astronomy & Cosmology / Re: Who claimed that gravity is a curvature in spacetime?

« on: 21/04/2018 15:50:31 »

If I didn't get lost in the calculations, for the metric of an uniform gravitational field (mentioned in your link), R⁰₀₃₀ is not zero. So it is not a flat spacetime, even without tidal forces.

It is true that in the case of a uniform gravitational field, for the reference frame of an observer in free fall, the spacetime is flat. The same spacetime would be curved for an observer not in free fall.

That would be the case for a spaceship with uniform acceleration in outer space, and the RF of an astronaut jumping from the ship, compared to the others staying there.

But for a more conventional gravitational field, as the existing around the Earth, an observer in free fall (as the astronauts in the ISS) is not in a flat spacetime. It seems very flat indeed in the spatial range of that small ship, and if the period of observation is also small. After some minutes, looking through the window, the Earth will be rotating around. And geodesics should be straight lines for a flat spacetime.

So gravity is a curvature in spacetime, in the meaning that there is no gravitational field without that curvature, and no curvature without gravitational effects.