سوال حول المشتري

[bahlol]

ارجواممن لديه اختصاص في الفلك ان يجبني على سوالي المتعلق حول المشتري هل فعلا تم رصد عكس حركته خلال السته اشهر الماضيه اي انه بدأ بالدوران عكس الاتجاه هل تم ذلك فعلا ام لا وهل يمكن ذلك مستقبلا ام لا

 

 

يهلول

[Maha Hussam]

Translating Bahlool's :ترجمه

I would like that whoever is an expert on this to please answer my question about Jupiter. Has it been really noticed that its orbit has been rotating in the counter direction for the past six months. Did that really happen or not, and could it happen in the future

[Guest Guest_aabir sabeel]

dear bahlol,

i'm not an expert in astronomy and i did not hear about these news, but i'm quite sure that this is imposible, and that's been established long time ago by Galileo as a general rule in physics when he mentioned that all objects are in motion unless it is been affected by an external force like the friction, air resistance, magnetic fields or some other factors and in case of Jupitor which is the largest planet in the solar system, and its size is bigger than all the other planets put together, even if there is some forces that could act on it, they are negligable, so nothing can turn it to the opposite direction.

about the other part of the question, i can't predict what will happen in the future but i can tell you that even if this could happen it will be in the far far far "and you could add more fars to that" future.

the reason why i'm saying this is that the most recent astronomical reseaches now are talking about developing a kind of reckets to could defend the earth against the asteroids, and that should be done by setting off the reckets from a space ship.

the scientists hope that this could be done in the near future.

the asteroids are of different sizes, but even the largest one could not even be compared with a planet like jupitar.

so, that's imposible, at least in the near future.

hope this answers your question.

[deepSqueaker]

hi bahlol,

 

I'm no astronomer or cosmologist, either, but I had studied Physics in college. I am pleased that you actually observed this orbital behavior by Jupiter. I don't often get to watch the sky. What you describe is called retrograde motion. I will try to explain but hopefully someone could translate.

 

The Earth moves relatively faster around the sun that does Jupiter. Our year is much shorter. As the earth's orbit is inside Jupiter, we occasionally pass it, like running around a track. Now picture a wall of stars on the other side of jupiter. These stars don't move. If you picture Earth, Jupiter and the stars, you can see that when observing from earth, jupiter looks to be next to some stars on the wall. As earth passes Jupiter, it looks like jupiter falls backwards, since you will see jupiter next to stars that were behind it before. After awhile, the earth orbits around to the side of the sun and then the retrograde slows, then stops and jupiter finally starts going in the right direction again.

 

Note: Jupiter actually moves faster than the earth in a straight line. It's linear velocity is higher. However, these bodies are in orbit so what is important in this case is which is faster around the sun. Even though the earth moves slower, it has less distance to travel around the sun. It's orbital frequency is higher. frequecy = 1/period. So a longer period, or wavelength, results in a higher frequency. An electric motor works by having magnets rotate (orbit) around a coil, which can generate electricity at the same frequency - for an AC generator. This is the area in physics where Newton invented calculus and applied it to orbital mechanics, and that generated the field of waves. On one of the new Iraqi dinars, there is a 10th century mathemetician named Al Hazan, I think. He invented a theory of optics that is still used today! Unfortunately, I forget the equation of motion for an orbital body under the influence of gravity, though. sorry.

 

hey! Welcome to the free world!

Cheers,

Rob

[deepSqueaker]

"So a longer period, or wavelength, results in a higher frequency."

 

oops. This should read

 

So a shorter wavelength, results in a higher frequency.

 

period is when you watch something oscillate track the time it takes to return to the starting point. wavelength is if you draw the position over time on a grid and it is the distance from peak to peak. Think of water waves. Period is the time between waves and wavelength is the distance between the peaks. ok, I am officially of topic, now ;-)

[Guest Guest_aabir sabeel]

hey Rob,

i wish you know arabic then you will notice that my answer was the right one for the question in arabic while yours was the right one for the same question translated to english to which i didn't pay attention assuming it is the same, but actually the translation was a bit modified !!

i understand completely what you've mentioned about what it " looks like " the motion in the oppsite direction but i'd like to know why do you think the linear speed of jupitar is higher than the earth and how do you know that.

what i know is that the orbital speed of the earth is 29.79 km/s

and that of jupitar is 13.7km/s

so i'm refering here to km per second and not to km per period so i can imagine that if we measure both in km/sec. and the orbital speed of the earth is higher, then the linear speed of the earth should be also higher and that is not because the earth is obsolutely faster, but because of its position to the sun.

as you know, the orbital speed of the planets are lower as you go further away from the sun and the reason behind this - in my opiniun -is the effect of the gravity which is according to Einstein, a curvature in spacetime is more on nearer planets than the farher ones because of the acceleration, just like when you throw a stone from a top of a building, the speed will be the highest when the stone is closest to the ground.

i'd like to know your feedback on this

[deepSqueaker]

hey aabir sabeel,

 

where did you get your data?

 

Basically Kepler's 2nd law governs this orbital speed. A body in an elliptical orbit sweeps the same AREA in unit time. Let's imagine a comet. When the comet is far away from the sun, the gravity is weaker, and the comet is moving slowly. In a given unit of time (1 month let's say) the comet will only traverse a very small degree of it's orbit (0.05 degree let's say). You can compute the area of that triangle. Now let's look at the comet when it is very close to the sun. It is now moving much faster, because the gravity is stronger. So in the unit of time, it will traverse a much greater degree of it's orbit (let's say 2 degrees). You can compute the area of this triangle. The areas of both triangle will be the same.

 

I think that orbital velocity is also called angular velocity and the velocity vector actually points above the plane of the orbit, following the right-hand rule.

 

As I said earlier, the earth is faster around the sun. It sweeps greater angles in a unit time than jupiter. This allows retrograde motion as earth laps jupiter. However, the linear velocity is higher in jupiter. The reason why relates to how the US Space Shuttle has to do orbital manuevers and it seems like it is counterintuitive. Here is the deal, if your space shuttle (the Iraqi Space Shuttle? You ought to build one!) is in orbit at some distance from the earth, and you want to go to a lower orbit, what do you do? Since this is physics, we always want to simplify the problem. Ok, so instead of a space shuttle, lets use a spherical camel. ;-) No air resistence.

 

Seriously, we are in a circular orbit, not elliptical. We want to go to a lower orbit. This would be the same as being in Jupiter's orbit ad changing to Earth's orbit. What you do is thrust backwards which acts as a brake to slow you down. Since you are moving slower, your orbit bends faster from gravity and that moves you to a lower orbit (balancing all the angles to prevent going into an elliptical orbit, of course). Now the funny thing is that you move ahead of the old orbit. What I mean is that if you drop a banana peel off of your spherical camel so that it stays in the old orbit, as you slow down and drop to a lower orbit, you will actually move ahead of the banana peel, since it will take you less time to make a complete orbit.

 

I hope this helps!

 

cheers,

Rob

 

ps. check out: http://en.wikipedia.org/wiki/Physics

[Guest Guest_aabir sabeel]

nice try Rob and nice sense of humer, you should keep some for the Christmas!!

but my question was simple yet deep, and it seemed to me that you kept explaining the same answer to the previous question of bahlol just like somebody trying to explain the water by saying it's something watery. and still did not answer my question.

my qustion was simply, why do you think that the linear speed of Jupiter is faster than that of the earth ?is it the momentum or is it something else related to the nature of things. why should any object, celesial or in quantum physics be faster than any other object, why should the neutrino which is massless should be slower than the photon which is massless too. and when i asked how do you know that? i meant if you have Jupiter and the earth in absolute space without the effect of external power, is there any way to know which one is faster or which direction they are going to take supposing they are far enough from each other that there is no effect between them whatsoever. hope you review my question.

i thought you would give it a deeper thought and trying to be more imaginative instead of copying some laws in physics well known to anybody who studied college physics or even high school physics so the discussion will be more creative.

if you still don't know what the equation for circular motion is, it is :

ac=v^2/r

by the way, they say the long neck in the camel is a good feature,,,, you know why?!

so that he has sometime to think before he make sounds

cheers

[deepSqueaker]

ok. aabir sabeel, I'll extend you the benefit of the doubt and assume that you are getting a little over-enthusiastic. I don't have a whole lot of time to spend, but I thought this an interesting area to discuss and I wanted to participate in this blog. Your post to which I was responding, included some incorrect physics. Yes, this may be high school physics, but it relies crucially in stating the problem the correct way.

 

At the end of your previous post, you based your imagining of a relationship between angular velocity and linear velocity of an orbiting object as analogous to acceleration of a dropped object. Nope.

 

"the orbital speed of the earth is higher, then the linear speed of the earth should be also higher and that is not because the earth is obsolutely faster, but because of its position to the sun.

as you know, the orbital speed of the planets are lower as you go further away from the sun and the reason behind this - in my opiniun -is the effect of the gravity which is according to Einstein, a curvature in spacetime is more on nearer planets than the farher ones because of the acceleration, just like when you throw a stone from a top of a building, the speed will be the highest when the stone is closest to the ground.

"

 

as you know, angular velocity and linear velocity are entirely different. In fact, to completely specify the classical state of an object, including orientation, you have to specify the vector of linear position, vector of angular position, the vector of linear velocity and the vector of angular velocity all at a well known time. Then you identify the forces that affect that object and you can compute the state of the object at later times.

 

you are thinking the linear velocity vector of Earth and Jupiter are radial to the sun. This is incorrect. The linear velocity is tangential to the orbit. Recall that if you could flip the gravity of the sun off, then earth would continue straight in a tangent to it's orbit. The absence of gravity no longer accelerates the earth in an orbit. If you did turn off gravity, aside from nausea, Jupiter would travel faster. For a relativistic model of this, recall the demonstration where a stretched sheet has a rock in the center and you roll a ball around it. As friction SLOWS the ball, it drops to a lower orbit and it's period increases. (it loses energy...)

 

Your observation that a dropped stone vertically accelerates is correct. However, this has nothing whatsoever to do with velocity of a stone in a stable orbit. Stable orbit means there is no radial velocity!

 

Ok, since you asked, I will go deeper and build an analogy of my own. I am amused that you are linking relativity and quantum mechanics, but we really aren't ready to discuss QED or QCD are we? Nonetheless, let's look at quantum mechanics. An atom, with bound electrons, is in a particular energy state. This includes the electronic energy level of the electrons. Since it is an atom and not a molecule, there are no vibration or rotational energy levels. There are several quantum numbers needed to describe this, but let's ignore all of that. So this atom is hanging out and along comes a photon of just the right frequency such that the fields resonate and the atom absorbes the photon. This causes an electron to move to a higher electronic energy level. If enough photons of the right energy levels come along, that electron will eventually have enough energy to be unbound. Consider that fact that more absorbed energy takes the electron to a higher shell and eventually will free it. Sounds like escape velocity...

 

A higher orbit in classical terms is also more energetic. More energy would imply a higher momentum. No increase in mass occurred (or negligible - heck, mass is nothing but energy anyway) so it must have been velocity. This should answer your question. (see Hamiltonian and Lagrangian energy equations in mechanics)

 

I'll leave relativity and limits of observability to someone else to get into. My geodesics are rusty.

 

Cheers :-)

[aabir sabeel]

good enough Rob

i'm wondering if you have your own proposals, i'm not trying to challege or something but i was thinking it could be a good place to post some geniuine ideas, proposals or theories, something that cause interaction of thoughts of different people and at the same time will be entertaining.

after all, it was the most fascinating theories that arises from people who did not accept for granted what was considered as a rule.

i think lots of people will be interested in posting and discussing their ideas here.

before doing that though, it should be checked with the administration of this website whether they have in their policy of the legal copyrights or so.

[deepSqueaker]

aabir, my own proposals about what? I mean give me some starting point, because without a starting point, there is no basis from which to build associations of ideas. I think this statement has deep implications for the current philosophy thread, since the recent points made there has devolved into whether all observations about the universe can only occur through subjective instruments of humans. I believe you are stating that this requires logic to be a part of the physical universe.

 

I disagree with that. Logic is a human invention. Like all good models, it is self-describing. Likewise, the universe is probably self-describing to some extent. Mass and information can both be viewed as energy. An interesting aspect about self-describing systems is that there is a very finite set of primary elements and a dynamic that combines the elements to produce new elements. It is a generative system.

 

In the case of the universe, let's just consider energy with no form. No mass and no information. There is nothing. Now imagine that a partition occurs which divides this energy into an inside (space) and an outside (notspace). The inside defines the beginning of time and the beginning of space. The outside is energy. As the inside interacts with the outside, energy (ex)changes and the inside divides itself into two. This is now a self-describing system.

 

Interestingly, the first sentence in Genesis, shared by all the Abrahamic religions, is something like:

 

"In the beginning, god created the heavens and the earth"

 

This self-defines the system. This is all you need to make the rest happen. We have time, space, matter, force and action.

 

 

so...what do you think? It's great that we can rewrite history!

Cheers

[Guest Guest_aabir sabeel]

listen .... i don't know if you have problem understanding what i'm saying or not and i don't care ... i never demand something ...in my last comment i was suggesting .

if you are trying to read my mind the way you want, that's your problem, and if you want to put something for discussion, that's up to you, nobody cares if you do or don't so stop thinking like you are the center of the universe, and if you keep commenting the way you are, then nobody will even look at what you are writing

 

chaw

[deepSqueaker]

aabir, I reread our posts and I did take what you were saying wrongly. I read this all wrong:

 

"i thought you would give it a deeper thought and trying to be more imaginative instead of copying some laws in physics well known to anybody who studied college physics or even high school physics so the discussion will be more creative.

"

 

of course, that may have beeen a result of my rather blunt question to you:

 

"where did you get your data?"

 

which I really meant sincerely. I really wanted to know how you found those orbital velocities. Perhaps you took this as challenging.

 

sorry about that misunderstanding.

 

If you are still interested, I'm really enjoying thinking about this stuff again and I'm very interested in what you think about my previous post, minus all my bullshit (which may very well entail the entire post!). Perhaps I should through it into the mix of the Philosophy thread, since it relates to creation myths. What do you think?

 

later

[aabir sabeel]

deepSqueaker,

please don't worry about it and you're most welcome to share your thoughts in the phillosophy section, i think there is some serious and entertaining discussion going on there and i'm sure it is a good idea to post your previous post there, i think it will add another dimentions to the discussion.

 

see you there