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#71
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Microgravity parable
Stuf4 wrote:
[snip] "NASA scientists call this microgravity... The term is apt since Albert Einstein said that acceleration caused by gravity is equivalent to any other push." The principle is about _mass_ equivalence, not acceleration equivalence. [snip] That is incorrect. It was the happiest moment in Einstein's life when he realized that an accelerated reference frame was equivalent to a frame in a uniform gravitational field. From this basis, Einstein could later show the equivalence of intertial and gravitational mass. But the first preceded the second. In the following, Einstein discusses how he came to believe there should be *no* preferred reference frame for the description of physical phenomena: "Then there occurred to me the ... happiest though of my life, in the following form. The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction. *Because for an observer falling freely from the roof of a house there exists--at least in his immediate surroundings--no gravitational field* [his emphasis in italics]. Indded, if the observer drops some bodies then these remain relative to him in a state of rest or of uniform motion, independent of their particular chemical or physical nature (in this consideration the air resistance is, of course, ignored). The observer therefore has the right to interpret his state as 'at rest.' Because of this idea, the uncommonly peculiar experimental law that in the gravitational field all bodies fall with the same acceleration attained at once a deep physical meaning. Namely, if there were to exist just one single object that falls in the gravitational field in a way different from all others, then with its help the observer could realize that he is in a gravitational field and is falling in it. If such an object does not exist, however--as experience has shown with great accuracy--then the observer lacks any objective means of perceiving himself as falling in a gravitational field. Rather he has the right to consider his state as one of rest and his environment as field-free relative to gravitation. The experimentally known matter independence of the acceleration of fall is therefore a powerful argument for the fact that the relativity postulate has to be extended to coordinate systems which, relative to each other, are in non-uniform motion." (Pais, A. (1982). 'Subtle is the Lord...': The Science and the Life of Albert Einsteing. Oxford: Oxford University Press. p. 178) So, Einstein would say that an ISS crewmember has the right to say he/she is in zero gravity. |
#72
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Microgravity parable
Stuf4 wrote:
From Mike Hanson: (Stuf4) wrote snip - Gravity is *distinctly different* from acceleration. While gravity has a property of acceleration, it is *not* acceleration. A 'g' is a unit of acceleration standardized upon a particular case of acceleration due to gravity (the gravitational acceleration at the surface of the Earth). snip I haven't posted here for a while. Decided to take a look, saw an interesting-looking thread title, and came across the above statement. You appear to have mangled your terms somewhat: *Gravitation* is distinctly different from acceleration. Gravity, however, is locally *indistinguishable* from acceleration. That this is so led Einstein to apply Occam's razor and postulate that they are one and the same phenomenon, leading to general relativity. And since GR has yet to be falsified, one can say that, to the best of our knowledge, gravity and acceleration are indeed the same thing (and hence that NASA is correct in its use of the letter g). This point regarding the equivalence theory has been addressed more than once on this thread... One easy way to determine whether you are accelerating due to gravity or not is to look out the window of your spacecraft to see if there are any stars or planets nearby. (I've suggested elsewhere that the root of this confusion in terminology is a misunderstanding of the equivalence principle.) ~ CT Note...I recently posted a reply pointing out that the Principle of Equivalence is *not* rooted in an equivalence between inertial and gravitational mass. Rather, it comes from the equivalence of inertial reference frames...those that are accelerating or equivalent to those in a gravitational field. Also, the nature of inertial mass is not fully understood and it is only postulated that inertial and gravitational mass are the same. Experiments carried out show this to be so to within great precision, but not infinite precision. |
#73
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Microgravity parable
Stuf4 wrote:
[snip] All I was saying was that one particular member has a published webpage that stands in complete agreement with the position I have been presenting. That member does not outline a position of belief that NASA scientists and astronauts do not understand gravity. So it is not in strict agreement with your position. [snip] |
#74
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Microgravity parable
Stuf4 wrote:
From Herb Schaltegger: (Stuf4) wrote: How ironic that you offer your extrapolation regarding "pretty much everyone..." while chastising my extrapolation. This reads as another form of "I'm right/you're wrong", coated with a heavy tinge of hypocrisy. And how many posters are publicly supporting your continued games of semanticism, pedantry, prevarication, equivocation and hand-waving? None. But let me guess: the lurkers all support you in email. Umm, they're not lurking. If you've been following the thread thoroughly you've seen that Jim Oberg's website has a page that fits in total agreement with what I've been saying here. So if, by assumption, Jim agrees with the position I have put forward, one might ask why he has remained silent. And an obvious follow up is to ask why others who might agree have remained silent. My best guess is that there is so much hostility among those who persist in abusive behavior that a silent majority/minority (?) prefer to sit out a would be scientific discussion. (3rd Reich lessons learned have previously been provided as to their application here at sci.space.) ~ CT Just to add fuel to this dwindling fire, Oberg, in a recent MSNBC column on the Chinese launch, says: " Moreover, Shenzhou’s solar arrays, unlike those on Soyuz, can rotate to track the sun while the spacecraft itself is aligned for other purposes, such as Earth observation or long-term microgravity drifting flight. The Russians did put rotating solar panels on another of their manned spacecraft, their Salyut-class space stations, and for exactly this same reason." See http://www.msnbc.com/news/979759.asp?cp1=1 Did you find the word "microgravity"? Hmmmm. |
#75
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Microgravity parable
Herb Schaltegger wrote:
(Stuf4) wrote: The statement you are quoting has been accepted physics since it was spelled out in detail in Isaac's Principia. You and Newton on a first name basis these days? Come on, give the guy a break. What he stated is a fact. Gravity is a FORCE. Acceleration is the result of a force being applied to a mass. Assasinating a character even when he says something that makes sense devalues the newsgroup. It is, as far as I know, still in the "sci" hiearchy and not in the "psy". Analyse the facts, not the personality. Experiments on the station should really be relabled as "free floating" instead of "0 g" or microgravity. "Microgravity" should be for experiments that happen *really* far from the earth where the gravitational force is truly "micro". As I recall, gravity at the altitude of the space station is still fairly powerful. The fact that gravity is still pulling objects down in the space station may not matter for current experiments where free fall is sufficient. But later on, when they start to study gravity seriously, it will matter. |
#76
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Microgravity parable
In article ,
Harry Kim wrote: Herb Schaltegger wrote: (Stuf4) wrote: The statement you are quoting has been accepted physics since it was spelled out in detail in Isaac's Principia. You and Newton on a first name basis these days? Come on, give the guy a break. What he stated is a fact. Gravity is a FORCE. Acceleration is the result of a force being applied to a mass. Assasinating a character even when he says something that makes sense devalues the newsgroup. It is, as far as I know, still in the "sci" hiearchy and not in the "psy". Analyse the facts, not the personality. Experiments on the station should really be relabled as "free floating" instead of "0 g" or microgravity. "Microgravity" should be for experiments that happen *really* far from the earth where the gravitational force is truly "micro". As I recall, gravity at the altitude of the space station is still fairly powerful. The fact that gravity is still pulling objects down in the space station may not matter for current experiments where free fall is sufficient. But later on, when they start to study gravity seriously, it will matter. That was so sweeping in it's supidity and ignorance that I don't even know where to begin. Therefore, I'm not bothering to snip any of it, so others can revel in it as well, "Ensign Kim." You just hop back aboard Voyager and warp on off to the Delta Quadrant, 'mmm 'kay? -- Herb Schaltegger, B.S., J.D. Reformed Aerospace Engineer "Heisenberg might have been here." ~ Anonymous |
#77
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Microgravity parable
"Herb Schaltegger" wrote in message
... You just hop back aboard Voyager and warp on off to the Delta Quadrant, 'mmm 'kay? Kim's just jealous because it was Paris and not himself that got to make it with the Captain. Nevermind that they had both turned into salamanders at the time. -- If you have had problems with Illinois Student Assistance Commission (ISAC), please contact shredder at bellsouth dot net. There may be a class-action lawsuit in the works. |
#78
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Microgravity parable
I had assumed that those who referred to their in-orbit experiments
as being in "microgravity" did so because they were being careful to acknowledge that despite their free-fall relative to Earth their experiments might still feel the (micro) gravitational attractions of other objects such as the surrounding spacecraft and nearby astronauts. |
#79
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Microgravity parable
Bruce Janson wrote:
I had assumed that those who referred to their in-orbit experiments as being in "microgravity" did so because they were being careful to acknowledge that despite their free-fall relative to Earth their experiments might still feel the (micro) gravitational attractions of other objects such as the surrounding spacecraft and nearby astronauts. As opposed to saying "zero-gravity". Yes. The debate is on the common usage of the term "microgravity", as to whether it is being used correctly given that at LEO distances, Earth's gravity is still quite strong. |
#80
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Microgravity parable
Bruce Janson wrote: I had assumed that those who referred to their in-orbit experiments as being in "microgravity" did so because they were being careful to acknowledge that despite their free-fall relative to Earth their experiments might still feel the (micro) gravitational attractions of other objects such as the surrounding spacecraft and nearby astronauts. Those gravitational attractions are negligible. The micro-g they refer to is due to the fact that most of the Station does not lie precisely on the orbital path of the Station center of mass. The orbital velocity is different at different altitudes, so portions of the Station which are above or below the center of mass will feel a radial acceleration away from the center of mass. Portions of the station which are to the left or right of the center of mass will feel a horizontal acceleration toward the orbital plane of the center of mass. |
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