Damming rivers slows down Earth's rotation

[aerius]

Yup, that's what I heard from a classmate in a Geography class today. We're discussing various environmental issues related to power generation when he mentioned this one. According to my classmate, damming up rivers puts more water at a higher elevation than normal, and this messes with the angular momentum of the earth's rotation and slows down how fast the planet spins by a measurable amount. I just gave him a blank look and was like "ummm...sure..." while all the BS detectors in my head are screaming "red alert!". I haven't taken physics in a few years so I can't put numbers or anything to it, but my gut feeling tells me that damming rivers has less effect on the Earth's rotation than tidal drag, and that this amount is so small that it's effectively zero. What do you guys think about this, pure BS or is there something to it?

[salm]

it sounds like a big truck load of bullshit. i mean the amount of water in rivers is effectivly zero compared to the water in oceans. ( i dont know that but i assume it).

[Wicked Pilot]

The total amount of water on earth is insignificant to the mass of the earth. It is also insignificant to the amount of stupidity of your classmate.

[weemadando]

This reminds me of one girl in a year 12 physics class...

"Why when a babies born doesn't the mass of the earth increase?"

That girl is now studying medicine. Be afraid. Be very, very, very goddamn afraid.

[Durandal]

ROTFLMAO!!!!!!!!!!!

Sorry, but by his reasoning, every time you rise from a sitting position, you'll cause a global catastrophe!

[Darth Wong]

That reminds me of a late 19th century idea that skyscrapers were bad because they would affect the rotational inertia of the Earth (you know, by sticking up so high). I guess the people behind this idiotic notion forgot how Mount Everest makes the biggest skyscrapers look like toothpicks

[HemlockGrey]

My personal favorites, from a middle-school science classes. Names have not been changed, because these 'innocents' do not deserve protection. I swear to God that these are all 100% true and said with PERFECT and UTTER sincerity.

Class A; headed by a teacher who would NEVER tell a student they were wrong.

Ifra: Why is it that even though the Earth's core is hot, it's cold in the ocean?

Mrs. Meluzio: Because...the...ocean...always has a bottom!

Ifra: Even if it's a muddy bottom?


***

Ifra: Can we go to the Earth's core?

Mrs. Meluzio: No, because the Earth's core is too hot.

Ifra: What about it winter?

***

Mrs. Meluzio: And so, the Titanic...

Rachel: Did you know that they think that Jack may have been a crewmember of the Titanic?

Mrs. Meluzio: Really?

***

Class B; headed by a guy who has had multiple nervous breakdowns;

Mr. Long:(describes how rocks burn up in atmosphere, detailed and in-depth)

Danielle: If meteorites know they're going to burn up, why don't they avoid the Earth?


I have many fond memories of that class...such as Danielle screaming that the teacher was a pervert, or the 'Doorframe of Shame' where I once saw posted a paper which had recieved a -20...


Don't worry. My current science teacher is ok.

[kojikun]

Mr. Long: ::pics up a rock:: This rock knows its going to hit your head. It thinks you're an idiot so it won't dodge you. ::fling::

Girl: OW!

Mr. Long: Fucker.

[Sebastin]

Actualy i read the same thing a couple of years ago in a very respectable source. (I don´t remember which one, i just remember that it was a good scientific source). But the idea was not the mass being farther from the center but being more imbalanced because the majority of all dams is on the northern hemisphere. The effect was also not measured but calculated and so small that it wouldn´t have any side effects. The whole thing went more under the header "Interesting little trivia"

I´ll try to dig up my source. It was most likely the Spektrum der Wissenschaft (german issue of scientific american)

[Spanky The Dolphin]

Go kick your friend in the crotch. He deserves it for saying something that stupid out loud.

[ArmorPierce]

Yes, stupid people deserves to be kicked in the crotch. Especially when they believe what they are saying is true.

[Stormbringer]

Go kick your friend in the crotch. He deserves it for saying something that stupid out loud.

And as they're dubled over on the floor, kick them in the head. We wouldn't their last few brain cells to die of loneliness.

[tharkûn]

Well it likely does change the moment of inertia a negligable amount. Just like it you walk against the motion of the earth you end up slowing the earth a negligable amount.

However NOTHING will be observable from these actions. In terms of practical results, nothing has changed.

[kojikun]

Just as a note: Because earth is a closed system, any change enacted by us stuff on earth is undone.

Meaning: If you want in a manner that would slow earths rotation, when you stop the energy you gained would be retransmitted into the earth. And if you walked in such a way that sped up the earth, then you stopped then earth would start pulling on you again and slow down.

And more damns further from the equator wouldnt slow the spin but speed it up. When water moves towards the equator, its adding to the mass at the equator and would slow it down, because its not moving as fast. But by adding to the mass towards the equator and slowing the earth down, it also increases the amount of power required to slow the earth because the added mass is harder to slow. Or something. ::

[aerius]

I thought it sounded kooky when I heard it, and now that I've had the chance to look some things up in my old physics and geology textbooks I know that it was a crackpot idea. The mass of all the water on this planet comes out to 0.022% of it's total mass, of which 98% is saltwater, 1.8% is frozen in icecaps & glaciers, and a measly 0.2% is what we get in rivers and lakes. Right...even if dammed up every body of fresh water it still wouldn't do a damn thing. And this is a 4th year university class...one has to wonder when the education system lets people like my classmate (who's *not* my friend) get this far.

[Spoonist]

More on the same topic:

Did you know that if all chinese jump at the same moment they would cause an earthquake?
(Take a good look at the map and come back to me).

There was this kidnapped spy who was taken on a submarine. After a while he told his kidnappers that they had crossed the equator. Do you know how he knew?
On the northern hemisphere the swirl in the toilet go clockwise in the southern hemisphere it goes anti clockwise.
(Stick your head down the toilet and flush, maybe you will see something that helps your reasoning).

Superman is so strong that he can lift himself.
(Yipiie I'm stronger thatn superman, I can lift myself and a backpack at the same time).

If you can travel counter clockwise around the earth in less than 24 hours you arrive before you left.
(Ever heard about the date line? And no there is no smooching at the end of it).

If the polar caps melt only mount everest will be above waterlevel.
(So that's why I spill my drink everytime that the ice melts in it).

Medicine gives more side-effects than herbal remedies.
(That's right, so run away take some belladonna, opium and we will discuss afterwards).

Because we dig up so much material from the earth and then send rockets into space the earth is getting lighter.
(I've heard of this thing called meteors, have you?)

If you are pushed into space from a spaceship you explode.
(True. If you are in a james bond movie you will).

You cannot drown in foam because there is air in the bubbles.
(Godie, go test that and give me a call from the morgue when you are finished).

Earth is a perpetual motion machine.
(Here is a dicionary, please go and look under perpetual).

Because computers do all the thinking for us mankind will become more and more stupid.
(Sure, if people thought like you).

Humans are the most advanced form of life.
(It would be a contradiction of terms for you to say that).

Smoking can't be bad for you since I feel better when I smoke.
(You'll feel no more pain when you die if that's a consellation).

That my kid is fat now means nothing, when he/she grows up he/she will become slim.
(And you're fat because?)

Since you can't convince me that you are right, I know that you are wrong.
(You have 10 seconds to convince me that you deserve to live).

Science is a religion.
(So if I stop believing in my computer it will stop working?)

You can never prove anything.
(Just because you can't doesn't mean it's impossible).

Scientifically a bee can't fly.
(Scientifically you can't think).

Humans only use 10% of their brains.
(In your case that's true but for the rest of us...)

Regeneration is impossible.
(So that's a new species that has grown out of my newts tail, how quaint).

Since I didn't learn the metric system in school it must be much more difficult than the imperial system.
(All I'll say is decadecimal).

Home schooling is better than public school. (USA)
(Even though your mom is smarter than you, I'd doubt that she knows all there is to know).

[Crown]

Spoonist I laughed my ass off, but if I may just one nitpick?

If the polar caps melt only mount everest will be above waterlevel.
(So that's why I spill my drink everytime that the ice melts in it).

I know what you mean, but Antarctica is on a continental shelf, so the snow on it, isn't really apart of the ocean, any more than the sky scrapers of New York are in the harbour, for example. That's all.

[Singular Quartet]

Actually, its humanity using Earth to slingshot objects into space that's causing the Earth to slow down. This, however, has just become barely detectable. I figure that in a few decades, we'll be building gigantic rockets just to get the Earth's rotation back to the correct speed.

[Lagmonster]

Mr. Long: ::pics up a rock:: This rock knows its going to hit your head. It thinks you're an idiot so it won't dodge you. ::fling::

Girl: OW!

Mr. Long: Fucker.

This was so funny that I laughed out loud at work, causing my lab assistant to wonder what the hell I was doing.

[Spoonist]

Spoonist I laughed my ass off, but if I may just one nitpick?

If the polar caps melt only mount everest will be above waterlevel.
(So that's why I spill my drink everytime that the ice melts in it).

I know what you mean, but Antarctica is on a continental shelf, so the snow on it, isn't really apart of the ocean, any more than the sky scrapers of New York are in the harbour, for example. That's all.

Quite correct. Maybe we will loose belgium, and some coastal areas if they melt. That's it. It's not going to be the end of the world.

Another Thera though, that would be a disaster...

->Singuler quartet
What's wrong with slowing down?
The moon has slowed us down for millenia upon millenia and noone has complained yet.

"Earth's rotation is decelerating at a rate of about 0.002 seconds per day per century. "

[Lagmonster]

...And this is a 4th year university class...one has to wonder when the education system lets people like my classmate (who's *not* my friend) get this far.

Shoot them now, before they get out into the world, are mistaken for educated professionals, and given control of something important.

[Nick]

For the 'walking and it's effect on the Earth's angular momentum', there's a couple of concepts worth considering:
1. There are lots of people & animals on Earth, all moving in different directions. If all directions are equally likely, the net momentum relative to the surface of the Earth is likely to be zero.
2. Newton's third law. In order to oppose the rotation of the Earth (by walking west), you are applying a force which pushes the surface of the Earth east.

On the northern hemisphere the swirl in the toilet go clockwise in the southern hemisphere it goes anti clockwise.
(Stick your head down the toilet and flush, maybe you will see something that helps your reasoning).

Are you trying to say the coriolis effect doesn't occur in submarines?

If the polar caps melt only mount everest will be above waterlevel.
(So that's why I spill my drink everytime that the ice melts in it).

The ice in your drink is almost completely submerged before it melts. A lot of the ice in the polar caps is above sea level.

Medicine gives more side-effects than herbal remedies.
(That's right, so run away take some belladonna, opium and we will discuss afterwards).

Quite possibly true, since many 'herbal remedies' work by nothing more than placebo effect. (i.e. they don't have any effect, let alone side effects)

You can never prove anything.
(Just because you can't doesn't mean it's impossible).

Depends on the definition of 'prove'. If they mean 100% proof, then (to steal Mike's example) it is impossible to prove that they aren't a brain in a vat, and the rest of the world their delusion. Consequently, it is impossible to prove anything (since it might all just be an arbitrary delusion).

In the real world, it is generally possible to demonstrate that something is so, but impossible to prove that it is so. My advice is to stay away from the word 'prove'. Too many mathemeticians and non-scientists always try to ascribe it the '100% certain' meaning - and the necessary reliance on the principle of parsimony always leaves room for modification in light of future understanding.

Humans only use 10% of their brains.
(In your case that's true but for the rest of us...)

For some reason, people always miss out the 'for conscious thought' which should be tacked on to the end of this statement (and even then, I'm still not sure if it is particularly accurate).

Since I didn't learn the metric system in school it must be much more difficult than the imperial system.
(All I'll say is decadecimal).

The US government has an interesting approach. . . metricisation by stealth! All the businesses that deal internationally have to cope with it, so they make their suppliers cope with it, which means they all want employees who can cope with it, which means it eventually makes it into the school curriculum. All without the government having to mandate a changeover :>

(I still think it's funny that the UK has switched to SI units, while the US, land of the free, uses a measurement system whose namesake is the British Empire. Didn't they fight a war to get rid of British influence?)

[Lagmonster]

Because computers do all the thinking for us mankind will become more and more stupid.

I'm actually marginally annoyed about how technology is used to allow the stupid the luxury of being stupid. I'm not saying it's bad. I like safety in my technology. I just have to accept that much of technology lets the dumb to dumb things because they know the technology is carefully designed by intelligent people to let them get away with it.

Or, take the 50 or so guys a year who are admitted to hospital for trying to masturbate with a vaccuum cleaner. The addition of razor blades in the nozzle would simplify things greatly, not to mention make the problem of large objects caught in the hose a thing of the past.

If we really want to solve the idiot problem, we should design a device that harmlessly and painlessly delivers a drug-free experience of the most intense and pleasurable sexual experience possible in human existance, involving rapture up to and including the point of death. "It'll be the best you'll ever have, but you're probably going to die", we'll put on the box. I bet you couldn't keep them on the shelves.

[Nick]

Just for interest, a quick summary of what the coriolis effect is (I went and checked to see if I had remembered the term and the concept correctly).

http://zebu.uoregon.edu/~js/glossary/co ... ffect.html

Essentially:

An item travelling north in the northern hemisphere appears to be deflected east (as it is travelling eastwards faster than the surface further north, by virtue of being further from the axis of rotation)

An item travelling south in the northern hemisphere leads to a westwards deflection.

So spiralling systems (such as atmospheric cells, or uninfluenced water draining down a sink) in the northern hemisphere will tend to have the northern part heading east and the southern part heading west - in other words, the spiral goes clockwise.

For the southern hemisphere, because the direction of maximum surface velocity has changed (it is now north), the direction of the coriolis force changes.

In the southern hemisphere, an object moving north is deflected west. An object moving south is deflected east. This leads to spiralling systems which go anti-clockwise.

[Nick]

Ooops. . .

http://physics.about.com/library/weekly/aa071501a.htm

Looks like sinks are too small a scale for inertia to come into play.

Cool - learn something new every day :>


EDIT: This explanation of what the Coriolis effect is (and why it doesn't apply to the kitchen sink) might be easier to follow. . .

http://www.discovery.com/area/skinnyon/ ... inny1.html

(Have I mentioned lately that: a) the internet is cool, and b) I love Google ?).