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Author Topic: The Moons Closest Pass By the Earth in a Century, Storms.  (Read 9891 times)

Offline Titanscape

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Becuase of the moon's close pass, Sydney is stormy, our dam has mud in it and an oil tanker is run aground. There was off coast, high tide 10 m swell.

But we need the rain, wettest June on record in Sydney.


 

Offline kdlynn

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The Moons Closest Pass By the Earth in a Century, Storms.
« Reply #1 on: 28/06/2007 18:04:01 »
not to sound stupid... but how does the moon cause this?
 

Offline Karen W.

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« Reply #2 on: 28/06/2007 18:53:38 »
Well the moon has everything to do with the tide as I recall and I imagine that the tide has been way higher then usual because of that!causing I would think all of the above. I believe that the force of gravity must be stronger when the moon has passed so close but I know little about it too so maybe someone would explain a bit better .I do not know enough to explain and have probably botched it up pretty good!
 

Offline Karen W.

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« Reply #3 on: 28/06/2007 19:00:44 »
Here is a bit of explanation  from

http://library.thinkquest.org/05aug/00769/gravity/gravity2.htm


     Tides and gravity
Gravity is stronger when objects are closer to each other. High and low tide for example have to do with the moon. The moon is much smaller than the earth, but does tug the water in the oceans and creates tides. When is the tide high or low? The moon and the earth both turn around a common center of gravity.   

The gravity of the moon tugs water towards the moon where it is closest to the earth. If your are on the place where the moon is closest to the earth it is high tide. Later on the day the moon astronaut and the earth turn and the gravity becomes less, and it is low tide.The moon has less mass, so the gravity on the moon is less. That is why astronauts can jump so high on the moon.
 

Offline eric l

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« Reply #4 on: 03/07/2007 17:48:56 »
Here is a bit of explanation  from

http://library.thinkquest.org/05aug/00769/gravity/gravity2.htm
...      

The gravity of the moon tugs water towards the moon where it is closest to the earth. If your are on the place where the moon is closest to the earth it is high tide. Later on the day the moon astronaut and the earth turn and the gravity becomes less, and it is low tide.The moon has less mass, so the gravity on the moon is less. That is why astronauts can jump so high on the moon.

So you have a high tide where the moon is closest to the water (= right above you if possible).  But at the same moment you also have a high tide at the opposite side of the earth, which is why you have two hight tides and two low tides a day.  The link does not adequately explain that. 
I checked this one (which also links trough to a nice animation) :  http://science.howstuffworks.com/question72.htm
 

jolly

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The Moons Closest Pass By the Earth in a Century, Storms.
« Reply #5 on: 03/07/2007 21:16:51 »
Quote
What causes high tide and low tide? Why are there two tides each day?


The following diagram shows how the moon causes tides on Earth:

WouldŽnt let me copy it  [:-'(]!

Quote

In this diagram, you can see that the moon's gravitational force pulls on water in the oceans so that there are "bulges" in the ocean on both sides of the planet. The moon pulls water toward it, and this causes the bulge toward the moon. The bulge on the side of the Earth opposite the moon is caused by the moon "pulling the Earth away" from the water on that side.


That makes no sense it would pull the water on the other side to. If that were correct you would only have one high tide aday!
 
Quote
If you are on the coast and the moon is directly overhead, you should experience a high tide. If the moon is directly overhead on the opposite side of the planet, you should also experience a high tide.

During the day, the Earth rotates 180 degrees in 12 hours. The moon, meanwhile, rotates 6 degrees around the earth in 12 hours. The twin bulges and the moon's rotation mean that any given coastal city experiences a high tide every 12 hours and 25 minutes or so.

Sorry I do not except that arguement if the gravity pulls the earth it would pull the water to, so the water on the other side would not rise, it would be flat. I do not except that theory!
« Last Edit: 03/07/2007 21:24:06 by jolly »
 

another_someone

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« Reply #6 on: 03/07/2007 21:40:41 »
Quote

In this diagram, you can see that the moon's gravitational force pulls on water in the oceans so that there are "bulges" in the ocean on both sides of the planet. The moon pulls water toward it, and this causes the bulge toward the moon. The bulge on the side of the Earth opposite the moon is caused by the moon "pulling the Earth away" from the water on that side.


That makes no sense it would pull the water on the other side to. If that were correct you would only have one high tide aday!
 
Quote
If you are on the coast and the moon is directly overhead, you should experience a high tide. If the moon is directly overhead on the opposite side of the planet, you should also experience a high tide.

During the day, the Earth rotates 180 degrees in 12 hours. The moon, meanwhile, rotates 6 degrees around the earth in 12 hours. The twin bulges and the moon's rotation mean that any given coastal city experiences a high tide every 12 hours and 25 minutes or so.

Sorry I do not except that arguement if the gravity pulls the earth it would pull the water to, so the water on the other side would not rise, it would be flat. I do not except that theory!

I have to say that I understand your consternation.

I can understand that since the far side of the Earth is further away from the moon that the centre of the Earth, so the gravitational pull on the far side of the Earth will be slightly less than on the core of the Earth.

On the other hand, the moon is 16 Earth radii away from the moon, so the difference in gravitational pull should only be slight.  Against that is the very large difference between the mass of the Earth and the mass of the water resting upon it, and maybe more significantly, the substantial difference in stiffness (the body of the Earth, while still  having some elasticity, is certainly not a liquid).  Thus, for the same force, the water should be able to respond more quickly, and to a greater extent, than the main body of the Earth, and thus even allowing for the slight difference in gravitational force applied to them respectively, I find it difficult to see that the Earth would move more than the water on the far side of the Earth.

I had always (maybe erroneously) assumed that the opposite tide was due more to the water rebounding (maybe some resonant effect) than direct gravitational force.
« Last Edit: 03/07/2007 21:44:14 by another_someone »
 

jolly

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« Reply #7 on: 03/07/2007 22:00:54 »
Quote

In this diagram, you can see that the moon's gravitational force pulls on water in the oceans so that there are "bulges" in the ocean on both sides of the planet. The moon pulls water toward it, and this causes the bulge toward the moon. The bulge on the side of the Earth opposite the moon is caused by the moon "pulling the Earth away" from the water on that side.


That makes no sense it would pull the water on the other side to. If that were correct you would only have one high tide aday!
 
Quote
If you are on the coast and the moon is directly overhead, you should experience a high tide. If the moon is directly overhead on the opposite side of the planet, you should also experience a high tide.

During the day, the Earth rotates 180 degrees in 12 hours. The moon, meanwhile, rotates 6 degrees around the earth in 12 hours. The twin bulges and the moon's rotation mean that any given coastal city experiences a high tide every 12 hours and 25 minutes or so.

Sorry I do not except that argument if the gravity pulls the earth it would pull the water to, so the water on the other side would not rise, it would be flat. I do not except that theory!

I have to say that I understand your consternation.

I can understand that since the far side of the Earth is further away from the moon that the centre of the Earth, so the gravitational pull on the far side of the Earth will be slightly less than on the core of the Earth.

On the other hand, the moon is 16 Earth radii away from the moon, so the difference in gravitational pull should only be slight.  Against that is the very large difference between the mass of the Earth and the mass of the water resting upon it, and maybe more significantly, the substantial difference in stiffness (the body of the Earth, while still  having some elasticity, is certainly not a liquid).  Thus, for the same force, the water should be able to respond more quickly, and to a greater extent, than the main body of the Earth, and thus even allowing for the slight difference in gravitational force applied to them respectively, I find it difficult to see that the Earth would move more than the water on the far side of the Earth.

I had always (maybe erroneously) assumed that the opposite tide was due more to the water rebounding (maybe some resonant effect) than direct gravitational force.

You know what I also believe that its based on rebounding, really I feel the tide is affected once a day by the moon, the second tide is, in my opinion, a rebounding effect.
 

Offline ukmicky

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The Moons Closest Pass By the Earth in a Century, Storms.
« Reply #8 on: 03/07/2007 22:21:11 »
Basically the earth which we can see is made out of two substances water and solid and the two react to the pull of the moon by different amounts.

As the moon circles the earth its gravity moves the earth backwards and forwards away from and towards the sun.

Water being a fluid has a more pronounced reaction to the moons gravity than the solid mass and therefore on the side nearest to the moon it bulges which gives us a tide.  But at the same time the solid mass of the earth is also being pulled towards the moon . but the water on the other furthest away from the moon feels a lesser force of gravity andbeing a fluid doesn't react as quickly as the solid to the tooing on throwing of the earth and is sort of left behind which causes it to bulge which causes a tide.


I THINK THATS RIGHT?
« Last Edit: 03/07/2007 22:44:05 by ukmicky »
 

jolly

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« Reply #9 on: 03/07/2007 22:32:43 »
Basically the earth which we can see is made out of two substances water and solid and the two react to the pull of the moon by different amounts.
As the moon circles the earth its gravity moves the earth  backwards and forwards away from and towards the sun as it does the water on the other side of the earth furthest away from the moon being a fluid reacts to this movement slower than the solid mass causing a tide .

Water being a fluid has a more pronounced reaction to the moon gravity than the solid mass and therefore on the side nearest to the moon it bulges which gives us a tide.  But at the same time the solid mass of the earth is also being pulled towards the moon . but the water on the other side being a fluid doesn't react as quickly as the solid to the tooing on throwing of the earth and is sort of left behind which causes it to bulge which causes a tide

I THINK THATS RIGHT

It could be but your explaination is far more complex, than what another_someone suggested and what I also believe:
That the second tied is more about the water rebounding back in an attempt to settle, however it can not as quite soon afterwards the moon is over head again.
 

Offline ukmicky

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« Reply #10 on: 03/07/2007 22:41:55 »
Actually i got it sort of of wrong as its centrifugal force which causes the tide on the other side :)
Rather than the water being left behind the earths orbit with the moon around the common centre of gravity is pushing the water outwards in the opposite direction to the pull off the moon and the centrifugal force created causes it to bulge
« Last Edit: 03/07/2007 23:08:32 by ukmicky »
 

another_someone

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« Reply #11 on: 03/07/2007 23:30:06 »
Actually i got it sort of of wrong as its centrifugal force which causes the tide on the other side :)
Rather than the water being left behind the earths rotation is pushing the water in the opposite direction to the pull off the moon  and the centrifugal force created causes it to bulge

But would not centrifugal force apply to the water equally in all directions.  It may be why the water is higher throughout the world (at least at low latitudes) than it might otherwise be, but it would not show why the water is higher on the side away from the moon than it is on the sides that neither face nor are away from the moon.

Then again, maybe we are actually asking the wrong question.  Now I think about it a bit more, I half recollect a very different explanation.

The issue is not that the water away from the moon has been raised at all.

What we are seeing is the water on the side of the Earth away from the moon at its natural level.

What we are also seeing is water from the sides of the Earth perpendicular to the moon being sucked forward towards the moon - thus it is the exceptionally low tides on the bits of the Earth that neither face nor are away from the moon which is the anomaly, because their water has been sucked towards the side of the Earth facing the moon in order to feed the tides there.

 

Offline ukmicky

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« Reply #12 on: 04/07/2007 03:06:01 »
No i learnt this one a long time ago and i may not be able to remember it 100 but on the moon side the tide is caused by gravity ,on the other side gravity from the moon isnt strong enough to dictate and it is caused by centrifugal force and is caused by the earth rotating around the common centre of gravity between the earth and the moon

THERE HAS GOT TO BE SOMETHING ON THE WEB.
 

Offline eric l

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« Reply #13 on: 04/07/2007 13:45:54 »

THERE HAS GOT TO BE SOMETHING ON THE WEB.

I suppose that everyone is Googling by now, but only in English.  So I tried a couple of other languages.  I found this link in French, which I'm not going to translate (it is rather long), but the graphics are eloquent.
The French article blames the high tide on the opposite side on centrifugal forces.
http://www.ifremer.fr/lpo/cours/maree/forces.html

Other links that I found refer to differences in attraction by the moon between "here", the centre of the earth and "the opposite side" which would result in "negative differential attraction" for the opposite side.  (A bit far fetched, I'm afraid).  (I'd better start reading that post on pasting diagrams)

By the way, the tides produce a sine wave variation in the sea level.  The period of this wave is very close to 4*pi.  Some people might call this a relevant indication for "intelligent design", I suppose.   
 
 

another_someone

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« Reply #14 on: 04/07/2007 14:48:41 »
No i learnt this one a long time ago and i may not be able to remember it 100 but on the moon side the tide is caused by gravity ,on the other side gravity from the moon isnt strong enough to dictate and it is caused by centrifugal force and is caused by the earth rotating around the common centre of gravity between the earth and the moon

THERE HAS GOT TO BE SOMETHING ON THE WEB.

As Eric has said, I can not find anything regarding the centrifugal argument as such; but what was mentioned, and makes some sense, and could well be pertinent to your centrifugal argument, is that the Earth/Moon system does not actually rotate around the centre of the Earth, but around a centre that is between the centre of mass of the Earth and the Moon.  Thus, although the centrifugal force of the Earth would not be pertinent, the centrifugal force of the Earth/Moon system would be pertinent, since it would place the side of the Earth away from the Moon further away from the centre of (i.e. the axis of rotation) the Earth/Moon system than the side facing the Moon.  This would imply that the side away from the Moon would be subject to greater centrifugal force from the Earth/Moon mutual rotation than the side facing the moon.
 

Offline ukmicky

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« Reply #15 on: 04/07/2007 21:16:15 »
I found this.

Quote
At the same time, an Earth tide and an ocean tide form on the opposite side of the Earth, directly away from the Moon. This second bulge forms as follows (focusing on the ocean tide alone, for clarity): The Moon and the Earth, like all pairs of bodies orbiting each other in space, actually orbit around their common center of mass (that is, the point where, if their individual centers were attached to opposite ends of a rigid stick, the stick could be suspended from a string and remain in balance).

In the case of the Earth-Moon system, the common center of mass happens to be inside Earth, about 1068 miles (663 km) beneath the surface along a line connecting the center of the Earth to the center of the Moon. As the Earth and Moon revolve around this point like dancers spinning with linked hands, all points on both bodies experience a centrifugal force. This centrifugal force has the same magnitude and direction at every point on and in the Earth (i.e., away from the Moon parallel to a line connecting the center of the Earth to the center of the Moon). Where Earth's surface is at any angle other than 90° to the line connecting the center of the Earth to the center of the Moon, water experiences a horizontal component of this centrifugal force. On the half of Earth's surface facing away from the Moon, this horizontal force overcomes the pull of the Moon's gravity and causes water to flow over the Earth's surface to a point on the side of the Earth directly opposite the Moon-facing tidal bulge. A second tidal bulge thus form on the side of the Earth facing directly away from the Moon. This bulge is slightly smaller than the Moon-facing bulge because the imbalance between the Moon's gravitation and centrifugal force is smaller at this point. (The Moon is closer to the Moon-facing bulge, making its gravitation stronger there, whereas the centrifugal force considered here is the same everywhere on the Earth.) The larger, Moon-facing tide is termed the direct tide; the tide on the opposite side of the Earth is termed the opposite tide.

http://science.jrank.org/pages/6832/Tides-Theories-tidal-action.html
and this

http://www.pbs.org/wgbh/nova/venice/tide_nf.html

« Last Edit: 04/07/2007 21:20:35 by ukmicky »
 

Offline eric l

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« Reply #16 on: 05/07/2007 14:13:06 »
Any idea of how important this centrifugal force (due to the rotation of the Moon-Earth system) may be ?
 
The Earth-Moon system spins at a rate of 1 revolution per 28 days (even a little more actually).  This would mean an angular speed of 2.6*10-6 radians per second.

Or, if my rough calculation is not too far off, in a net force equivalent to 3.75*10-6 g. 

Not exactly spectacular !!!

The centrifugal force due to the Earth's rotation round its own axis is about a thousand times that much !!!
« Last Edit: 05/07/2007 14:15:24 by eric l »
 

lyner

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« Reply #17 on: 05/07/2007 23:52:01 »
The Earth 'wobbles' as the Moon orbits it. The two objects orbit around their common centre of mass which is not far from the Earth's centre but not actually  at it.
The bits of the Earth that are on the side, away from the Moon, have more of this 'centrifugal force' than the bits which are closer to the Moon. So, in addition to the effect of the Moon's gravity - which causes a high tide on that side, there is 'extra centrifugal force' on the other side - causing a hight tide there, too.
The numbers give more or less the same forces acting each way so the two tides are about equal.
Of course, there is the effect of the Sun's gravitational field, which causes 'Spring Tides' and 'Neap Tides' over the course of a Moonth.
 

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