Titanomachy
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From: Dennis M. Hammes on 29 Nov 2007 03:11 Don Shepherd wrote: > 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 If you ever manage to mean something, you'll /know/. -- -------(m+ ~/:o)_| Gresham's Law is not worth a Continental. http://scrawlmark.org
From: Dennis M. Hammes on 29 Nov 2007 03:33 Lee Rudolph wrote: > "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 But if the moon is thus in a sense /inside/ the Earth, would it not be far more correct to say that the moon "knows" the Earth (in the Biblical sense)? -- -------(m+ ~/:o)_| Gresham's Law is not worth a Continental. http://scrawlmark.org
From: Dennis M. Hammes on 29 Nov 2007 03:48 Invisible Lurker wrote: > 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. > Being defined by the secondary, all five LaGrange Points are /always/ "far" outside the primary. L1: equigravitational point (between p1 and p2). L2: equitidal point (opposite p1 out the far side of p2). L1 and L2 center on p2. L3: equinodal point (opposite p2 out the far side of p1). L4: Greek point (60 deg ahead of p2 in p2's orbit about p1). L5: Trojan point (60 deg behind p2 in p2's orbit about p1). L3, L4, L5, and p2 center on p1. What the "moon" is "far outside of" is Earth's Rochelle Limit, i.e., it isn't a "moon" but one of a planetary binary in primary orbit about the sun. -- -------(m+ ~/:o)_| Gresham's Law is not worth a Continental. http://scrawlmark.org
From: Don Shepherd on 29 Nov 2007 05:01 Dennis M. Hammes wrote: > Don Shepherd wrote: > >> >> We're all bosons on this bus. >> >> Don > > > > Step to the back of the bus, then. > You've hadron too many. > Boy, you really lepton that! Don
From: Don Shepherd on 29 Nov 2007 05:05
Dennis M. Hammes wrote: > Don Shepherd wrote: > >> 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 > > > > If you ever manage to mean something, you'll /know/. > Good one! Don |