|
|
|
Siberia
SFN Addict
Brazil
2322 Posts |
 Posted - 11/28/2005 : 07:24:07 [Permalink]
|
| I suggest that, next thread he makes, we only reply with The Question(tm). |
"Why are you afraid of something you're not even sure exists?"
- The Kovenant, Via Negativa
"People who don't like their beliefs being laughed at shouldn't have such funny beliefs."
-- unknown
|
 |
|
|
Bunga
Skeptic Friend
Sweden
74 Posts |
Posted - 11/28/2005 : 09:25:17 [Permalink]
|
quote:
Originally posted by bigbrain
You don't understand very much, you are like children.
Gravity of the sun becomes important when the object has a large mass, when it's near the sun and when has a low velocity
It all makes sense now! That is why ammunition fired from a gun never, ever falls to the ground, it just keeps going.
After all, it has small mass and has a high velocity. |
|
|
|
Subjectmatter
Skeptic Friend
173 Posts |
Posted - 11/28/2005 : 10:38:29 [Permalink]
|
| Hey, I have tiny mass compared to Cassini, I could probably jump straight to Saturn! I might need a good run-up though. I'll use a motorcycle... |
Sibling Atom Bomb of Couteous Debate |
|
|
|
furshur
SFN Regular
USA
1536 Posts |
Posted - 11/28/2005 : 11:14:06 [Permalink]
|
quote:
Gravity of the sun becomes important when the object has a large mass, when it's near the sun and when has a low velocity
Ohhhh... [slaps forehead]
So this is what you are saying.
The effect of Gravity is proportional to Mass/velocity.
As the mass decreases the effect of gravity decreases.
As the velocity decreased the effect of gravity increases.
This brings a question to mind:
Are you stupid or something????
|
If I knew then what I know now then I would know more now than I know. |
|
|
|
bigbrain
BANNED
409 Posts |
Posted - 11/28/2005 : 11:58:52 [Permalink]
|
Originally posted by furshur
So this is what you are saying.
The effect of Gravity is proportional to Mass/velocity.
As the mass decreases the effect of gravity decreases.
As the velocity decreased the effect of gravity increases.
Read carefully at http://en.wikipedia.org/wiki/Newtons_Laws_of_Gravity#Newton.27s_law_of_universal_gravitation
Newton's law of universal gravitation
Newton's law of universal gravitation states the following:
Every object in the Universe attracts every other object with a force directed along the line of centers of mass for the two objects. This force is proportional to the product of their masses and inversely proportional to the square of the separation between the centers of mass of the two objects.
Given that the force is along the line through the two masses, the law can be stated symbolically as follows.
F = -G m1 m2 / r2
where:
F is the magnitude of the (repulsive) gravitational force between two objects
G is the gravitational constant, that is approximately : G = 6.67 × 10#8722;11 N m2 kg-2
m1 is the mass of first object
m2 is the mass of second object
r is the distance between the objects
It can be seen that this repulsive force F is always negative, and this means that the net attractive force is positive. The minus sign is used to hold the same value meaning as in the Coulomb's Law, where a positive force as result means repulsion between two charges.
Thus gravity is proportional to the mass of each object, but has an inverse square relationship with the distance between the centres of each mass.
Strictly speaking, this law applies only to point-like objects. If the objects have spatial extent, the force has to be calculated by integrating the force (in vector form, see below) over the extents of the two bodies. It can be shown that for an object with a spherically-symmetric distribution of mass, the integral gives the same gravitational attraction on masses outside it as if the object were a point mass.1
This law of universal gravitation was originally formulated by Isaac Newton in his work, the Principia Mathematica (1687). The history of gravitation as a physical concept is considered in more detail below.
Problems with Newton's theory
Although Newton's formulation of gravitation is quite accurate for most practical purposes, it has a few problems:
Theoretical concerns
There is no prospect of identifying the mediator of gravity. Newton himself felt the inexplicable action at a distance to be unsatisfactory (see "Newton's reservations" below).
Newton's theory requires that gravitational force is transmitted instantaneously. Given classical assumptions of the nature of space and time, this is necessary to preserve the conservation of angular momentum observed by Johannes Kepler. However, it is in direct conflict with Einstein's theory of special relativity which places an upper limit—the speed of light in vacuum—on the velocity at which signals can be transmitted.
[edit]
Disagreement with observation
Newton's theory does not fully explain the precession of the perihelion of the orbit of the planet Mercury. There is a 43 arcsecond per century discrepancy between the Newtonian prediction (resulting from the gravitational tugs of the other planets) and the observed precession3.
The predicted deflection of light by gravity is only half as much as observations of this deflection, which were made after General Relativity was developed in 1915.
The observed fact that gravitational and inertial masses are the same for all bodies is unexplained within Newton's system. General relativity takes this as a postulate. See equivalence principle.
[edit]
Newton's reservations
It's important to understand that while Newton was able to formulate his law of gravity in his monumental work, he was deeply uncomfortable with the notion of "action at a distance" which his equations implied. He never, in his words, "assigned the cause of this power". In all other cases, he used the phenomenon of motion to explain the origin of various forces acting on bodies, but in the case of gravity, he was unable to experimentally identify the motion that produces the force of gravity. Moreover, he refused to even offer a hypothesis as to the cause of this force on grounds that to do so was contrary to sound science.
He lamented the fact that "philosophers have hitherto attempted the search of nature in vain" for the source of the gravitational force, as he was convinced "by many reasons" that there were "causes hitherto unknown" that were fundamental to all the "phenomena of nature". These fundamental phenomena are still under investigation and, though hypotheses abound, the definitive answer is yet to be found. While it is true that Einstein's hypotheses are successful in explaining the effects of gravitational forces more precisely than Newton's in certain cases, he too never assigned the cause of this power, in his theories. It is said that in Einstein's equations, "matter tells space how to curve, and space tells matter how to move", but this new idea, completely foreign to the world of Newton, does not enable Einstein to assign the "cause of this power" to curve space any more than the Law of Universal Gravitation enabled Newton to assign its cause. In Newton's own words:
I wish we could derive the rest of the phenomena of nature by the same kind of reasoning from mechanical principles; for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards each other, and cohere in regular figures, or are repelled and recede from each other; which forces being unknown, philosophers have hitherto attempted the search of nature in vain.
If science is eventually able to discover the cause of the gravitational force, Newton's wish could eventually be fulfilled as well.
It should be noted that here, the word "cause" is not being used in the same sense as "cause and effect" or "the defendant caused the victim to die". Rather, when Newton uses the word "cause," he (apparently) is referring to an "explanation". In other words, a phrase like "Newtonian gravity is the cause of planetary motion" means simply that Newtonian gravity explains the motion of the planets. See Causality and Causality (physics).
[edit]
Einstein's theory of gravitation
Einstein's theory of gravitation answered the problems with Newton's theory noted above. In a revolutionary move, his theory of general relativity (1915) stated that the presence of mass, energy, and momentum causes spacetime to become curved. Because of this curvature, the paths that objects in inertial motion follow can "deviate" or change direction over time. This deviation appears to us as an acceleration towards massive objects, which Newton characterized as being gravity. In general relativity however, this acceleration or free fall is actually inertial motion. So objects in a gravitational field appear to fall at the same rate due to their being in inertial motion while the observer is the one being accelerated. (This identification of free fall and inertia is known as the Equivalence principle.)
The relationship between the presence of mass/energy/momentum and the curvature of spacetime is given by the Einstein field equations. The actual shapes of spacetime are described by solutions of the Einstein field equations. In particular, the Schwarzschild solution (1916) describes the gravitat |
"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
|
| Edited by - bigbrain on 11/29/2005 00:07:39 |
|
|
|
Fripp
SFN Regular
USA
727 Posts |
Posted - 11/28/2005 : 12:01:48 [Permalink]
|
Big Brain,
Are there man-made satellites in orbit around the earth right now? |
"What the hell is an Aluminum Falcon?"
"Oh, I'm sorry. I thought my Dark Lord of the Sith could protect a small thermal exhaust port that's only 2-meters wide! That thing wasn't even fully paid off yet! You have any idea what this is going to do to my credit?!?!"
"What? Oh, oh, 'just rebuild it'? Oh, real [bleep]ing original. And who's gonna give me a loan, jackhole? You? You got an ATM on that torso LiteBrite?" |
|
|
|
pleco
SFN Addict
USA
2998 Posts |
Posted - 11/28/2005 : 12:15:12 [Permalink]
|
| What bends light, since light has no mass and travels at extremely high velocity? |
by Filthy
The neo-con methane machine will soon be running at full fart. |
|
|
|
|
Bunga
Skeptic Friend
Sweden
74 Posts |
Posted - 11/28/2005 : 13:52:03 [Permalink]
|
Bigbrain, while it is true that we do not have a comprehensive knowledge of gravity or its cause(s), we do have several models which are remarkably accurate. Newton's Theory of Gravity is one such. Notice that I do not call it "Newton's Theory of Universal Gravity", for new information came to light (as tends to happen in science) a hundred years ago which shows that the theory was neither "universal" nor complete.
That is not to say that it is not accurate. At non-relativistic speeds, and especially at speeds below 0.1c, the difference is so small that it pretty much cannot be detected.
F = 1/c2Gr2 * §1E1/P2 dV * §2E2/P1 dV
This is the current model of gravity, and applies (as far as is known) "universally". The only change has been to replace the "M1" and "M2" with the integral over the density, to account for relativistic effects.
At the velocity which the Cassini - Huyugens probe will reach, the difference between the calculated gravitational attraction of the Sun to the Cassini probe in the two different equations is less than one part in a million. While this is still enough for it to be important over interplanetary distances, on the scale shown by the diagram on the previous page, it is irrelevant.
Enough on that, Bigbrain. On another note though, you should look up what a "theory" is, in terms of science. Wikipedia no doubt has a good article on it (unfortunatly I can't seem to open www.wikipedia.org for some reason). A theory doesn't mean "a guess" or "an estimate" or anything similar, when something is called "a theory" in terms of science, it is because it is known to be as "true" as anything can be through mere induction. |
|
|
|
bigbrain
BANNED
409 Posts |
Posted - 11/28/2005 : 15:15:48 [Permalink]
|
Originally posted by Bunga
F = 1/c2Gr2 * §1E1/P2 dV * §2E2/P1 dV
This is the current model of gravity, and applies (as far as is known) "universally". The only change has been to replace the "M1" and "M2" with the integral over the density, to account for relativistic effects.
This is the universal gravitation crap.
"Integral over the density" HA HA HA 
Dear Big Buffoon, go and work for BNB, increase the number of Big NASA Buffoons.
|
"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
|
| Edited by - bigbrain on 11/29/2005 00:04:22 |
|
|
|
filthy
SFN Die Hard
USA
14408 Posts |
Posted - 11/28/2005 : 15:54:50 [Permalink]
|
I've always rather liked this photo.
 |
"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist! 
|
|
|
|
Dave W.
Info Junkie
USA
26020 Posts |
Posted - 11/28/2005 : 17:03:02 [Permalink]
|
quote:
Originally posted by bigbrain
We know nothing about gravity, we have only poor theories.
Well, then your ideas that the effects of gravity on Cassini can be ignored because it was far from the Sun and of little mass are "poor theories." Too bad for you, you've shot your own argument in the head.
bigbrain, are there any man-made satellites orbiting the Earth today? |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
|
|
|
Randy
SFN Regular
USA
1990 Posts |
Posted - 11/28/2005 : 17:51:19 [Permalink]
|
quote:
Originally posted by filthy
I've always rather liked this photo.
filthy, Mimas and the big smack...that's been one of my favorites, too. Here's some recent ones from the Casinni site, Mimas photo journal...
http://saturn.jpl.nasa.gov/multimedia/images/images.cfm?subCategoryID=21
Click on the "Full Res Jpeg" to view....
http://photojournal.jpl.nasa.gov/catalog/PIA07639
http://photojournal.jpl.nasa.gov/catalog/PIA06582
Lot of wow factor with this one....
http://photojournal.jpl.nasa.gov/catalog/PIA06574
Just incredible, that Casinni mission.
====================
Hey bigbrain, why do you think there's no stars in those Mimas photos? (you've shown us you don't know jack-squat about photography 101...have you learned anything, yet?)
And, are there any man-made satellites in orbit around the Earth right now?
bigbrain, your fly is open. |
"We are all connected; to each other biologically, to the earth chemically, to the rest of the universe atomically."
"So you're made of detritus [from exploded stars]. Get over it. Or better yet, celebrate it. After all, what nobler thought can one cherish than that the universe lives within us all?"
-Neil DeGrasse Tyson |
|
|
|
filthy
SFN Die Hard
USA
14408 Posts |
Posted - 11/29/2005 : 04:16:15 [Permalink]
|
Voyager was a magnifenct project that far exceeded the goals and even the dreams of it's designers. It made history even as it made science.
What does your crowd think of this one, b?
|
"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist!
|
|
|
|
bigbrain
BANNED
409 Posts |
Posted - 11/29/2005 : 11:36:12 [Permalink]
|
Originally posted by Dave W.
quote:
Originally posted by bigbrain
We know nothing about gravity, we have only poor theories.
Well, then your ideas that the effects of gravity on Cassini can be ignored because it was far from
the Sun and of little mass are "poor theories."
Too bad for you, you've shot your own argument in the head.
Suppose the sun can attract Cassini with a big force.
Well, why have Big NASA Buffoons steered the probe round
the sun two times before going to Saturn?
What utility has had this manoeuver?
|
"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
|
| Edited by - bigbrain on 11/29/2005 11:42:00 |
|
|
|
filthy
SFN Die Hard
USA
14408 Posts |
Posted - 11/29/2005 : 12:10:19 [Permalink]
|
quote:
Originally posted by bigbrain
Originally posted by Dave W.
quote:
Originally posted by bigbrain
We know nothing about gravity, we have only poor theories.
Well, then your ideas that the effects of gravity on Cassini can be ignored because it was far from
the Sun and of little mass are "poor theories."
Too bad for you, you've shot your own argument in the head.
Suppose the sun can attract Cassini with a big force.
Well, why have Big NASA Buffoons steered the probe round
the sun two times before going to Saturn?
What utility has had this manoeuver?
Gravity sling, Boronhead, gravity sling. Do some study on centripedal force and you will easily figure it out for yourself.....
|
"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist!
|
|
|
 |
|
|
|
Topic Locked
