…before major disasters occur? Major as in flooding of coastline cities and intense seismic activity.
Well I venture to say that the moon crashing into the earth would be the worst possible disaster scenario.
Isn’t that pretty much the opposite of what was asked?
The moon is gradually geting further away from the earth, at 3.8 cm/year. It would take huge forces to get it to start moving closer. Not only would the tides get higher, creating flooding, it would also increase tectonic activity, making more earthquakes and volcano eruptions. It would also alter the orbit of sattelites.
It would also slow the spin of the earth, making days longer. That would take a while, though, so it wouldn’t be too worrying.
Ok, time for crap-o-math:
<footnote>
All this stupid math and now I can’t find the average tide height… which makes it all pointless.
So, to sum it all up, the force of gravity changes with the inverse square of distance. So if the moon was half as far away, the tides should be about four times higher.
usless crap-o-math that I spent quite a while looking up numbers for:
The mass of the earth’s oceans is 0.0014x10^24 kilograms, or 1.4x10^21 kilograms. The high tides are caused when the oceans furthest from the moon are less attracted to it and the oceans closest to it are more atracted to it. We’ll split the mass of the oceans in half, acting like there are only two oceans, and say they are 3/4 the diameter of the earth apart.
So, each ocean is 7x10^20 kilos. The mass of the moon is 0.07349x10^24 kilos, or 7.35x10^22 kilos. The moon is about 380,000 km away. The radius of Earth is 6378 km, so with that 3/4 we agreed on it means that the far ocean is 9567 km further from the moon than the near one.
The force due to gravity on the ocean is m1*m2/(r^2). The force on the far ocean is then 7x10^20 * 7.35x10^22 / ((380,000+9567)^2) and the force on the far ocean is 7x10^20 * 7.35x10^22 / (380,000^2).
So, completely ignoring scietific notation and significant figures, we end up with the oceans having forces of:
339016672775583586977479520793524 and
356301939058171745152354570637119
http://www.seds.org/nineplanets/nineplanets/earth.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
http://www.seds.org/nineplanets/nineplanets/data1.html
No, it would be 8 times higher. As Wikkit explained, the tides are caused by the moon pulling the closer side of the earth more strongly than the far side, stretching the earth. So it’s the gradient (differential) in gravity causing the tides. This goes as inverse cube of distance.
Interesting mathematics, there, Wikkit. Thanks. After I scoop up my brains and shove them back into my skull, I’ll give them another try. 
Interesting websites, BTW.
The moon was once 1/10 as far away as it is now. That means that the tides were once 1000 (that’s one thousand) times as high! If there had been a Bay of Fundy, that would mean up to 16 mile high tides. Even leaving that unlikely possibility, it means that a modest 5 ft tide would have been a mile high tide. That has got to be larger than any tsunami we have ever seen and rmember that was every tide, twice in every five hour period. Oh, I forgot to mention that the day was only 1/5 as long as it is now.
The tidal friction resulted in the transfer of angular momentum from the earth to the moon that resulted in the moving further out and the earth’s day slowing down. Since I see no way (short of some sort of wild encounter with another body) of transferring angular momentum in the other direction, the moon is not going to move closer. But if it did, I guess the day would have to grow shorter, not longer.
THe moon is not pulling up the tides the amount you see. The moon is just giving them a little pull that build up over the years/centuries. If we had no moon and no tide and POOF the moon appeared the tidal difference would be unmeasurable for a while. I don’t know what that while is though.
So it took centuries to build up to mile high tides. So what? Tides still vary with the inverse cube of the distance.
Yes, tidal force goes as the inverse cube of distance.
So, if the Moon were half as far, the tidal force would be 8x as great. That would be enough to cause coastal flooding, especially during storms. When the Sun and Moon align (at full or new Moon) there can be flooding, and the Sun’s tides are only 1/2 the Moon’s. Increasing the Moon’s by 8 would certainly cause some flooding.
There is a tidal flex in the solid Earth as well; the ground goes up and down every day by about 30 centimeters or so (I believe it’s 15 cm each way). Eight times the force may not translate directly into a tide 8 times higher, but it would certainly put more strain on the Earth. I cannot put numbers to this (and I suspect it would be very difficult), but my point is that you can put some qualitative limits on this.
Moving the moon in would be pretty difficult. The amount of energy it would take to move it in would probably melt it completely! I’d have to work out the numbers, but it’s late. Any takers?
Cite?
K2Dave said:
"THe moon is not pulling up the tides the amount you see. The moon is just giving them a little pull that build up over the years/centuries. If we had no moon and no tide and POOF the moon appeared the tidal difference would be unmeasurable for a while. I don’t know what that while is though."
That doesn’t sound right to me. I don’t see why the sea, which is really a very thin film of water (maximum seven miles deep on a sphere 8000 or so miles in diameter, almost like breath condensation on an apple) wouldn’t respond relatively quickly to such an event.
As an aside, the tides are a little more complicated than the Moon simply pulling more strongly on the near side of the Earth. The Moon and the Earth rotate around their common centre of gravity, which lies on the line between their centres. Because the Earth is much heavier than the Moon, their common centre of gravity lies within the Earth, close to, but not actually at, its centre. The Moon’s gravity pulls a “bulge” up on the close side of the Earth, and centripetal acceleration puts a bulge on the opposite side of the Earth, which is why we have two tides per day rather than one.
I think you’d get two tides per day even without rotation. The gradient of the moon’s gravity stretches the earth, trying to make it into an elliipse. The ocean ends up being an ellipse but the land is more rigid, so the ocean is higher on two opposite sides of the earth.
Sorry no cite I was taught this in a geophysics class, If you want I can give you the proffesors phone number and you can call him up and ask.
With your calculations you get a tide of several miles which we all know isn’t the case. But if it is just a slight nudge over the years that build up harmonicaly you don’t get tides of that magnitude due to damping effects.
An urban legen is still an urban legend, even when it’s told by someone with a PhD. How would a tide be “built up”? Where would the energy be stored?
I’ve read that some bays have a natural oscilaltion frequency of nearly 12 hours, which the tides excite. The tides in these places get higher than you’d expect from a simple calculation. Perhaps that’s what k2dave is thinking about?
can you give a cite to support your argument?
Since when was it SOP in any forum here for the people who don’t blindly accept anecdotal evidence to need a cite to do so?
Tides can’t happen if you don’t have big, connected oceans. Were there big oceans during the time period in question? Was the crust completely solid? If the earth’s crust broke into a bunch of smaller plates tomorrow, the tides would be greatly reduced because the earth would heave and ho, rather than the oceans.
The earth (land) does some movement due to tides. Also the earth is 3/4ths covered by water. Your theory leads to tides miles high when the moon was closer which there is no evidence of.
Also there are tides in large lakes so I don’t know what you mean when you say that tides can’t happen if you don’t have big connected oceans.
Tides would be reduced if the oceans were divided up into smaller sections due to the break in the momentum.
While trying to find a cite that would support either my theory that tides built up over time or wilkit’s theory that tides are only to do with the gravity at the time. I have found some interesting items - not of which matter to our theorys but help w/ the OP.
1st lets get this one out of the way:
From http://k12science.ati.stevens-tech.edu/curriculum/tide.html
tidal waves are low frequency, long wavelength waves. Waves store energy.
Also the most notable thing is that the gravity doesn’t create the tides, the diference of gravity from one side of the earth to the other created the tides.
from http://hyperphysics.phy-astr.gsu.edu/hbase/tide.html#mstid .
This is deceptive. Although they are occur in water, they aren’t really “water” waves. Furthermore, they aren’t even waves in the normal sense, since they are broken up by the continents. And even if they were waves, that wouldn’t explain how their energy is stored. There are waves that store energy, but they store energy in specific ways. Simply being a wave is not sufficient to store energy.
Some of the other statements are questionable:
I guess it’s a bit of a nitpick, but all celestial bodies exert graviatition on the earth.
Why would the waves be higher during a high tide?