Is a Chinese Dam Slowing the Earth's Rotation?

No

According to this article in Newsday, the day may be lengthed by a miniscule amount.

"Even the filling of the Three Gorges Dam in China will have an effect: According to Chao's and Gross' calculations, it will lengthen the day by 60 billionths of a second."

I'd really like someone to explain the physics behind this. The planet is a closed system with respect to these phenomena. Wobbly though it may be, with an ever-migrating magnetic pole and continually changing axis, I don't see where the overall energy change comes from.

Incase no one else covered this yet; and at the risk of being wrong:

The planet isn't really a closed system, the sun bombards the earth with energy continuously, and the black cold outerspace "soaks up" the radiation that is emmitted. But I don't believe that is relevant here.

What you are inquiring about is angular momentum. The best analogy I can think of to compare how creating a huge lake would slow earths rotation would be an ice skater. Liken the earth to an ice skater spinning, the earth also spinning on it's axis. The skater spins very fast with it's limbs all brought in (looks like a vertical pole). If the skater puts her arms out the spinning slows, and when she pulls them back in she speeds up again. Similar to the earth, if more mass is moved way from the axis of rotation the earth will slowdown, although the change in mass moment of inertia from this lake would be nearly indetectable.

There is a certain amount of energy in the spinning system, that is kind of like kinetic energy. Kinetic energy is a function of mass and velocity. Rotational energy is a function of mass moment of inertia and angular velocity. The mass moment of inertia is a way to say where the mass is located from the center. If all of the mass of a body was located at the axis (impossible so imagine) there would be no angular momentem in the system reguardless of how fast it may be spinning. What the ice skater is doing to increas her angular velocity is reduce her mass moment of inertia.

Straigt from wikipedia:

is the angular momentum of the particle,

where

is the moment of inertia of the object (in general, a tensor quantity)

is the angular velocity.

Check out http://en.wikipedia.org/wiki/Angular_momentum

No.

Really?

I havnt heard such big dam, just Yangtsi River Dam which has been built up and put into power supply now.

If you are interested in Chinese dam, pls contact me

cnpower wrote: "I haven't heard such big dam, just Yangtsi River Dam which has been built up and put into power supply now."

I believe it is the Yangtsi River Dam that is being referred to: according to Wikipedia it is located in "the scenic Three Gorges area, between the cities of Yichang, Hubei; and Fuling, Chongqing" in the Yangtsi River and will only be fully filled in 2009.

To answer the original poster's answer more fully: a dam raises the mean water level of a river system and so effectively transfer mass to a higher point on the surface of Earth. Since the angular momentum of Earth (actually, the Earth-Moon system) must be maintained, Earth's rotation slows down and the length of a day is increased, albeit by a minuscule amount.

Hi Jorrie: Nice to see another face on the board and also a very good answer. I was going to mention angular momentum regarding the Earth's rotation, but had not considered the moon as part of the system in this question. That idea would seem to open a whole new set of questions...

Hi Paul, you wrote: "... but had not considered the moon as part of the system in this question."

Yes, in the strict sense of the question, the Moon does not enter this equation - you're right! But, in the general effects on Earth's rotation, the Moon plays a much larger role than any dam we can build, or the amount of snow on the mountains...

In the final analysis, you have to consider the 'bigger picture', but where to stop is never quite clear! The practical thing to do is to leave out the insignificant ones - then the Moon wins all the way.

BTW, the ocean tides as the big Moon influence is in fact a fallacy. It is rather the tide that results in the crust of the Earth that causes the slow-down of Earth's rotation. The ocean tides produce a daily variation that almost averages out, as described on my web-site's tidal gravity.

Hi everybody!

When the Earth's volcanoes are erupting and that's happening since long long time ago, the Earth's geometry was changing and changing permanently in a disproportionated (and not counterbalanced) way each time; then I would assume that even so, something else it's coming to regulate these "apocalyptic" questions which concerns the scientific thoughts of worried peoples.

And for that I would take in account:

- the strong universal magnetic field's rules;

- the oceans movements compensating allot anything else accumulated as disproportions;

- the inner magma and all the hot core's work;

- etc, etc.......;

I think also that many well established undiscovered by us rules still are governing precisely volens-nollens this huge universal time clock.

Respectfully, Dumitru

Jorrie,

You believe this will slow down the Earth's rotation by a minuscule amount. I'm curious. Do you think this will have an effect on the atmosphere?

I remember about 2 years they were saying the days were getting shorter. The 2004 Indian Ocean Earthquake caused as a tsunami and "shortened the length of a day by 2.68 microseconds", http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake. Philosophically, maybe the Three Gorges Dam is just a result of Newton's Third Law.

Interesting concept!

China is very populous, that's true and the dam is proportionally !huge! relative to other human made dams. It is !gigantic! from the perspective of the beaver and the lake will be for !fantastic! investment in boating.

Other than that, and the unfortunate impact on the displacement of people and animals and other environmental factos and a phenomenal amount of gigawatts produced ... I can't imagine it will do a dam-ned thing!

However, I have not studied this penomenon and therefore am not writing with the authority that your question demands. I recommend you ask Al Gore.

To name a few variable inputs:

Check the displaced body of water of the dam against the the rotational forces of the earth plus the movement of magma internally to the earth and the movement of the tectonic plates along with the tides and the movement of ice relative to global warming, the pull from the moon and the sun, namely the rotational forces affecting the earth's orbit, the movement of cars in Tokyo, Los Angeles, Paris and Frankfurt (to name a few) ... all versus time... and you can get millions of dollars in financial grants... after you present the "politically correct" essay!! Personally and privately, I believe, humans, really do not impact nature's behavior much beyond irresponsinbility and lack of respect.

Good question and a force to have us all consider: Our (human) unfortunate impact on nature.

Hah! An opportunity for Don's Theory of Human Existence. Thanks, Karl.

Consider the biosphere as a whole, and as a single entity, teeming with life. It thrives on the resources supplied by its unwitting (witless?) granite and iron host which goes through its own life struggles, shrinking, cracking, etc. This part is essentially taken from the Giai (sp?) theory. Now for the good stuff...

Some of the hosts writhings remove valuable resources from the biosphere - to wit carbon and hydrocarbons trapped under ground where life cannot reach them. What's a biosphere to do?

Answer: Create an "anti-body" with the intent of returning those long-buried treasures to the organic whole. That's us! Like all good antibodies we are spawned, take a while to determine our purpose, then go about it whole-hog until we are done. Like all good anti-bodies we then disappear save for a few in case we are needed again.

So... The purpose of mankind is to get all the oil and coal etc. out of the deep ground and put it back in the biosphere, preferably quickly, then to get out of the way. It is very convenient for nature that our efforts will also result in our demise rendering unnecessary the wait for another asteroid.

No. There is an overall conservation of energy.

What does happen is that energy is being transfered gravitationally

from the friction of the tides on earth to the moon.

So, the earth loses energy and slows down, while

the moon gains that energy to produce a higher orbit and it also slows down.

Newton had it all figured out 400 yrs ago.

So will this time be added to daylight hours, meaning that we'll have longer work days, or can we finally get a little more sleep?

And If we all climb up in huge ladders at night, (and put animals up in the upper floors of ten-story barns) and then come down at dawn, will that work to stretch the night a bit more?

And what if everybody suddenly dropped flat on the ground on April 14? Could we then whirl past Tax Day?

We would just have longer days and nights, because the earth would be turning slower ever so slightly...

But hahaha, yeah, I suppose if everybody in the world got up higher at night, and then parked their cars on top of the nearest mountain, we might get a couple extra nano seconds of sleep... but then we would be screwing the other side of the world out of 0.0000000002 seconds of night time!

Very interesting. the post cause so much discuss. In fact, it had a huge argument in the past in China and in the world. The bone of contents was whether we should build up the Dam. Dispute is intensely. opinions from the world are very different. at last, goverment of china dicided to set up the dam in 1994.5.20. and was delared to finish on 2006.6.6. now the huge reservoir began to fill and power is supplying. This dam is known-well Sanxia Dam (three gorges dam).The scenery is very beautiful and every year the tourists from world come to visit its significant vision. It sits close to Yicang city in Hubei province and Chongqing. If anyone would like to visit the place, I shall be glad to be guider! I also advice all of you to visit. There is no only one this dam along the Yangtse river (we call it " Chang jiang" in chinese pronaciation) but several dam seat on the river. they play an important role in chinese economic. I live beside Yellow River, the scond river in China. and has also many dams across it. When I was a boy I lived in a city where there was one of the famous yellow river dam! Return to the subject. I dont know the chao's theory because its out of my math depth. with regard to angular momentum in the EearthMoon quality system I think, if we calculate vey precision, there will be some affection on movement of earth. becasue accordingto the theory, even a butterfly can be cause the different movement. From other opion, human begin to launch many times rocket year by year. Some of them even fly away this system. How shall we deal with these questions? and their huge propellar force is most greater than these of the filling of water in many reserviors in a unit time and ther direction are all very same. just think of it,from quality and momentum conservation law, our earth will become more and more irregulation. Now we go back to chao's theory agian. Its not our tech can solve, just depend on political officiers. I thnk. I think the Sanxia dam is a good construction, it can adjust water and supply power and irrigate farm field. we can get many advantage from it. but there are lots of corruption officers bringing up with it as well.This is the last thing we would desire. But we can do nothing about it. OK, forget it. lets back to dam area. its beautiful scenery and worth to travel to visit, beside itself there are many other scenery around it. Welcome all to come to visit. I can help you all in China when you have any trouble. info@ndt.cn

OK !

Now, a question for our friend in China along the Yang-Tse:

Are you concerned about the lake effect or about the massive amount of tourism to effect the earth's behavior?

I have just traveled approx 6000 miles since my first response to you and I think I will take you up on your offer to assist interests in China.

Big dams are being built in Iceland also and experience can be shared.

Regards,

Karl

Hi, Karl, Its my pleasure to answer you. Im out of work and have to stay at home, nothing to do all day long so I have enough time to answer any question about our homeland :) Are you from Iceland? congratulate on your land being building up a big one as large as ours. Im sorry I dontknow the effect of lake. and dont know mass of tourists affection on the behavior of our earth as well. Im not an geographer. I just watch, tourism bring abounding of benefit to poor place. Of cuase it bring about many polution to the place. Not all of us are civilized people. not all of goverment will take out some of income to reduce the polution. are you satisfy with the answer? with regard to concentrate the water into a reservior, if it would affect on the earth movement. not any student will be able to work out it according to physics law. and it seems no use in our living.

difference of angle momentum (or say, momentum torque)= integral[(m1v1 dr)-(m2v2 dr)]; where m=f(r,t), v=g(r,t); r= redius of earth.( sphere coordinates system) whereas Frt= delta( angle momentum), something like rocket launch or atomic explosion. the force si very large or huge and time is very short. the change of anglemomentum is certainly larger than action of reservior. who could work out exactly? only mothod of statistic calculation. how shall we measure the day's long as precision as post offered? who will do the work?

There is still nobody out there willing to spend their leisure time to solve above simplified triplex integral. I found as well, although the equation is simplified and we have our own home computer which is enough strong function, we couldn't do it yet, because it still has many unkown parameters to bring forth.

I suppose if we build up many symmetrical dams on our earth, we have got a symmetrical reservoirs. So that, we could get a still balance earth. Im an idealist.

b

agin

Hi!!

I notice that you have time now. I wish you get better.

Just one question. i do not know lot of China geografy and I want to know a litle. Have you condenates to see it in google earth?.

Regards!

Delmar

Yes, and so does every newborn on this planet!

ZC

The effect is tiny in comparison with the sum of all other multifarious infuences that affect the earth's rotation.

Putting more mass into the atmosphere, by converting stored hydrocarbons into water and CO2, has a greater effect: the carbon and hydrogen once stored in underground reservoirs are raised to higher elevations and the energy to do this has to come from somewhere.

Constants are not an option.

Guest wrote: "The effect is tiny in comparison with the sum of all other multifarious influences that affect the earth's rotation."

Correct. The biggest effect by far is the tidal friction that the Moon causes on Earth. Tidal gravity is a very interesting topic and very often misunderstood. It is treated with an engineering 'spin' in the free PDF download from the web page Tidal Gravity.

What did the fish say when she bumped her head?

Dam!

Where did the fish go AFTER she bumped her head?

To the Dock!

Energy does not desapear, just change.

The earth is in constant change due to natural equilibrium. On big change somewhere will be follow for a reacomodation of the entire planet.

I belive that will change the rotation time for a while. But the complete escenarium, planets, galaxies and so on; will contribute to the this change became stable.

Trying to reach the equilibrium something for something small a small change will hapend. For something big something big will happend. Big does not mean fast or xtreme :).

Saludos!

Delmar

Hi, on the italian Wikipedia it says that the Three Gorges Dam slows Earth Rotation, every second will last 1,000000060, not 1. 2 Nasa scientists tell so. I calculated that in 12 years and half this error makes a second, so during this time the Earth will need a second more to accomplish normal rotation! Sorry bad english.

Ok, consider the effect of a fluid dampner on rotational harmonic vibrations of an internal combustion engine. Wouldn't the large areas of the earth's oceans act like a dampner on the added off center weight of the Three Gorges Dam? How about all the granite, stone and heavy materials that have been used for building materials in the United States over the past 300 years? Dubai, and any other man made areas, the removal of underground oil is being replaced with building material there.

Anything that has the potential to change the angular momentum of a ratating body will change the speed of rotation. This is proven physics. Whether this dam will change the dynamics of the earth's rotation or is up to mathematicians. My concern is that should a change occur then that would have an impact on our earth's distance from our sun. Can we now consider 'climate change' vs. human? If we have been led to beleive that humankind can effect 'climate change' then should we not examine the causes & whether there are vested interests in promoting carbon over more plausible & historic changes?

The effect is miniscule in comparison with other factors. The day length varies by a few milliseconds ordinarily depending on the average direction and average speed the wind is blowing.

Though calculable, it is therefore not detectable.