Titanomachy
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From: Don Shepherd on 28 Nov 2007 20:46 Ned wrote: > > But one question... If all motion is relative, how does > the earth know that the moon is revolving around IT, rather > than IT revolving around the moon? > > Ned > > What does it mean to say that the earth "knows" something? Don
From: Ned on 28 Nov 2007 20:47 "Don Shepherd" <donshep2.nospam(a)verizon.net> wrote in message news:URo3j.50965$Pt.45933(a)trnddc02... > >> But one question... If all motion is relative, how does >> the earth know that the moon is revolving around IT, rather >> than IT revolving around the moon? >> Ned > > What does it mean to say that the earth "knows" something? > Don > What does it mean to say that one thing goes "around" another thing, when all motion is relative? Ned
From: Lee Rudolph on 28 Nov 2007 20:52 "Ned" <nedludd(a)ix.netcom.com> writes: > But one question... If all motion is relative, how does >the earth know that the moon is revolving around IT, rather >than IT revolving around the moon? It would be better to say (all "relative"ness aside, and more than adequate approximations being taken for granted) that the Earth-Moon system rotates around ITS center of gravity (which is, however, beneath the surface of the Earth, giving some standing to the knowledge you impute to the earth, above). Lee Rudolph
From: Don Shepherd on 28 Nov 2007 21:03 Ned wrote: > > > What does it mean to say that one thing goes "around" another > thing, when all motion is relative? > > Ned > > What does it mean to say that something means something? Don
From: Invisible Lurker on 28 Nov 2007 23:02
Ned said: > "tadchem" <tadchem(a)comcast.net> wrote in message > news:62d7fd94-63ee-4322-9087-acd0f710efa9(a)t47g2000hsc.googlegroups.com... >> >>> I don't buy it. The earth's rotation is slowing down. It is >>> slowing down for the same reason that the moon (and all moons) >>> slow down and ultimately present the same 'face' to the object >>> they are circling: The gravitational pull of the larger object >>> inhibits the rotation of the smaller object. >> >> What you are saying here is that "The gravitational pull of the >> larger object (Earth) inhibits the rotation of the smaller object >> (the moon)", which is a fait accompli. The moon no longer rotates >> relative to the gradient in the earth's gravitational field. >> What you are ignoring (or mis-stating) is that the *differential* >> gravitation (tide-raising force) works both ways, so the moon's >> gravitation (and to a lesser extent the sun's as well) is what >> is slowing the earth's rotation. >> The earth is not perfectly rigid. It flexes as it spins in the >> moon's gravity because the part that is facing the moon feels a >> stronger gravitational effect from the moon than the part facing >> away from the moon. >> Tidal friction converts kinetic energy of rotation to thermal >> energy, while the total angular momentum of the system is >> conserved. >> The earth is still spinning fast, but friction from the interaction >> with the moon's gravitational field raises tides in the water and >> the land, heating both while slowing down rotation. When the earth >> has slowed enough that it keeps one face towards the moon, then the >> interaction with the moon's gravity will no longer produce tides, >> and the sun's gravity will become the main factor slowing down the >> rotation of the earth. >> http://en.wikipedia.org/wiki/Tidal_locking >> http://www.badastronomy.com/bad/misc/tides.html >> http://www.jal.cc.il.us/~mikolajsawicki/tides_new2.pdf >> Eventually, if the sun, earth, and moon last that long, the moon >> and earth will recombine and become a single body locked into >> position facing the sun (at the moment I don't want to calculate >> how long that may take). >> Tom Davidson >> Richmond, VA >> > > Oh, take a shot. Is it more like a billion years or more > like a 100 million years? > > But one question... If all motion is relative, how does > the earth know that the moon is revolving around IT, rather > than IT revolving around the moon? > > Ned The moon is so large that it is essentially a binary system with the LaGrange points far outside the earth. The moon is no puny satellite. -- Invisible Lurker Really Not Here or There, Either |