Our orbit is the balancing act betweeen the Sun's gravity and the Earth's kinetic energy. If the former were greater, Earth would fall into the Sun; if the latter were greater, we would move outwards, and possibly leave the Solar System.

Any object which has mass - whether or not it has a molten core - generates a gravitational field, and that is what holds satellites in orbit. The magnetic field, if any, is irrelevent.

Nice discussion.

I don't think we need yet another terrestrial body to transfer the angular momentum to but Venus could have had a moon too that took over angular momentum and swarfed away due to coming too close to the sun. That moon could also have been a double planet? perhaps we know that moon now as "Mercury". I don't know. Pure speculation.

Let us look at Earth's precession. the Earth spin axis follows a cone to be completed in only about a mere 26,000 years. This is caused by an external torque force imposed on Earth by the sun and moons gravity difference to the equatorial bulge of the earth. What does this do to the constantness of the Earth angular momentum, Nothing? forget it. Angular momentum and torque are really vector quantities. its direction is always along the axis of rotation.

So the torque force of Sun and Moon on Earth is big enough to change the direction of the spin axis (and consequently the vector direction of the angular momentum) to over about 47 degrees in only 13,000 years (opposite sides of the precession cone and double the tilt of the Earth). When doing a three directional vector analysis we see that the vector components of Earth angular momentum have changed considerably, although the absolute value of the vector sum remained constant.

Now we're getting close.

I believe the massive amounts of static electricity that is present in populated areas could be a source that could combine with other influences to "slow down the earth"

...and for the moon it keeps us balanced and in check, like a magnetic motor

Well, I might as well mention it, since this is a Geological forum.

Tidal sediments called "rythymites" show that the Earth has indeed slowed down in its rotation (and that the period of lunar cycles has increased by 4 days from 25 days from new to new Moon, to 29.5 days.)

The problem is, this is not a constant change, it began to significantly alter around 900Mya. This suggests that it is more related to the shifting of the Continents than to anything else.

Anyway, have fun with all your stupid phsyics BS, but it's patently wrong, the geological records proves that, unless you can establish another variable to account for the changes in the rate of change.

Well keeping it strictly physical, I can think of three main reasons possible for a change in the rate of spin of the Earth,

Change in angular inertia of the Earth due to mass shifting, maintaining angular momentum

Transfer of angular momentum to the moon due to tidal drag

Transfer of angular momentum to the sun and moon due to inner core drag resistance to the precession of the equinoxes and the obliquity cycle.

I agree with Andre here he is pretty knowledgeable when it come's to this stuff, and the stupid physics BS that your talking about is in everyones life everyday and it effects everyones life from day to day. some people understand it and I guess some don't.

also if you haven't noticed since the 9.0world seismic event there was a small noticeable change in the rotation, where I live in the middle of the USA the sun raised around 6:45 to 7:00am now just one day after when I get of work at the hospital at 7am its still dark and the sun doesn't show itself til 7:30 and the moon is still high in the sky. Call it crazy, call it what ever but its kinda funny how the change happened overnight.......so do you stiff think physics is stupid.........this is a science forum.

Are you kidding about the abrupt change in daylight hours? Surely. It would have affected the whole planet, not just middle America.. and I certainly haven't noticed!

Now, the earth is rotating faster then before, so it is not slowing down anymore. With the recent Tsunamis from the Indian Ocean, the planet’s rotation has begun to wobble and speed up. In addition to the huge movement of water, a subduction zone caused from the tectonic plates has reduced the circumference of the earth, thus making it spin faster. – This is just like how a figure skater spins faster when they bring their arms in. This means we now spin faster and as a result have a shorter day. We may even perceive a small rise in the oceans water levels, which can further effect the rotational speed of the earth.

Why would the planet speed it's rotation? The way I heard it was that lunar gravity puts gravitational strain on earth (tides and such), causing the wealth of geological activity we have. Think about it, that takes alot of energy, it has to come from somewhere. Law of conservation of energy says that this massive energy doesn't just come out of nowhere, and it doesn't. It snatches it's energy from earth's rotation. Think of Earth being a spinning brake disk in a car, the moon being the pad attached to the frame, and by heating up the disk slows down. So why the hell would the planet SPEED UP from geological activity!!! It just doesn't make any sense! I'm probably begging to be corrected here so please do.

Evidence please.

Evidence please.
Although huge from a human perspective, the volume of water was vanishingly small on a global scale.
The movement had no discernible effect upon the Earth's circumference. Provisional assessments of seismic data indicates the edge of the Burmese plate moved up.

I think you misrepresented what my meaning is, taking a literal translation instead of contextual (more important).

Physics is BS, by itself, and the majority of answers have gone off the deep-end ignoring reality, which involves mechanics, something General Physics deeply ignores. The physics used in this forum is all "ideal" and ignores the fact (finally mentioned by Andre) that a change in angular momentum due to mass relocation is a factor.

More than "a factor", it is now considered THE factor. Before mass-distribution became a variable on a large scale with the shifting of Continents, the slowing of the rotation was not at as high a rate as it was aftewards.

And in any case, your idea that there is a noticeable change of rotation due to the 9.0 earthquake proves you must be off your kiester. I have noticed no such change and I am at a higher latitude than you (meaning the change should have been even GREATER than what you experienced).

Mass redistribution on the Earth will affect rotation speed in two ways, both related to your skater. If a large mass displaces downward toward the center of the Earth, then the rotation speed increases.

If a large mass moves poleward, toward the axis of rotation, the rotation rate also speeds up. The rotation rate slows of course if these masses move in the opposite direction.

I have been reading on wep pages and hearing in the news that the recent Sumatra Earthquake slowed the Earth's rotation rate a tiny amount, 3 microseconds a day, because a large mass suddenly moved upward, away from the center of the Earth. This is missleading because the upward slippage at the toe of the subduction zone was a rebound from several centuries of being pulled down. (Further back in the subducting plate the land had bowed upward, so the earthquake allowed this land to sink.) The effect over one several century long stick-slip cycle does not involve a net raising of land.

It would also be incomplete to think of this large subducing mass as a net downward movement into the Earth, or a net poleward movement. The reason that the plate moves is that rock is pushing on it. That rock originally came from upwelling magman at a mid-oceanic ridge. Long term, the mass rising at the mid-oceanic ridge is equal to the mass sinking at the subduction zone. There should be no skater effect.

One more thought. The experts' prediction that the Earth's rotatation speeded up 3 microseconds a day is the result of their computer projections, not of any actual observation. Be warry of accepting them as fact. We have a concept called GIGO in computer programming: Garbage In; Garbage Out. It means that if your computer model doesn't take everything into account that it should, or gives too much consideration or too little ot any one effect, then you are giving your computer model garbage, and should expect to see garbage in your results.

As to all this talk of earthquakes having a notable effect on the Earth's rotation: if they do, the sheer number of earthquakes which happen each year (most of them virtually unnoticed, well away from inhabited areas), should have a cumulative effect far greater than the gradual slowing of our planet's spin by the tides. And the planet must have been even more tectonically active in the distant past. The long-term slowing trend evidenced in the geologic record, which Freemason referred to above, would be overwhelmed - or at least hugely distorted. This is not the case.

Interresting thoughts...
Not sure I subscribe to changes in the Earth's period. Although the snap effect of the plate movements was geologically spectacular, I would say the shift in mass was not a reduction in the Earths's diameter. I would actually lean in the other direction. ie. The compression of the plates was reduced with the release of energy, in effect increasing the area.
If gravitatinal fields are distributed to the center of the mass, any change of distribution of mass on any object would change it's gravitational field.
Which in theory would have an effect, in this case on other terrestrial bodies.
Which would have an effect on angular momentum.

I’m not sure if this has been said or not, as I do not have time to read through all the replies, but I believe that the re-routing of water, etc. has a minimalist effect on the rotational velocity of the earth.

True, the earth’s rotation is slowing as days go by, but that slowing is the net effect of the moon distancing itself from the earth. Tidal friction - something that is not influenced by humans, is the primary factor in why this is happening. As rotational energy is passed to the moon through tidal friction, the rotation of earth slows [EDIT: and the distance between the earth and moon increases]. Eventually, there will come a time where the earth itself will be tidal-locked with the moon. The contrary is already the case with the moon. At that point, the earth-moon system will have reached a continuum where the only significant factor influencing the rotational velocities would be a change in diameter of the earth-moon system.

Let's not forget that the Sun will still produce tidal drag on both Earth and Moon, even after they are in rotational synchrony with each other.

Good point! As you may be able to tell, I rushed through that post, but what you said is understood.

At least you know what you're talking about; some of the misconceptions people post here are incredible. I may have been guilty of this myself, once or twice... let's see, in a few years' time, if any research papers on the Asian earthquake's long-term geological consequences are available, and if they mention an adjustment to our diurnal rotation.

I heard the earthquake opened hell and now dragons are taking over the earth... wait, scratch that, it was a misconception.