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Author Topic: Is The Earth Spin Slowing ?  (Read 3101 times)

Offline neilep

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Is The Earth Spin Slowing ?
« on: 21/06/2006 14:54:33 »
Did I hear, or read somewhere else here, that the spin of the Earth is slowing ?....I know it may be on a minuscule increment (If I heard correctly) but will the earth's spin stop before the Sun turns us into a Barbecue ?

If so...care to speculate what life will be like on a non spinning Earth ?...

....OR...have I got it the wrong way round and the fact is that the Earth is  gradually spinning faster ???...so...how long have we got before we're flung off ?

Thanks chumms xxxx

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another_someone

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Re: Is The Earth Spin Slowing ?
« Reply #1 on: 21/06/2006 15:19:37 »
http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT307/HTML/AT30706.HTM
quote:

According to the Earth Data box, Earth rotates once on its axis (relative to the stars) in 23h 56m—1 sidereal day. However, we know from fossil measurements that Earth's rotation is gradually slowing down, causing the length of the day to increase by about 1.5 milliseconds (ms) every century—not much on the scale of a human lifetime, but over millions of years, this steady slowing of Earth's spin adds up. At this rate, half a billion years ago, the day was just over 22 hours long and the year contained 397 days.
A number of natural biological clocks lead us to the conclusion that Earth's spin rate is decreasing. For example, each day a growth mark is deposited on a certain type of coral in the reefs off the Bahamas. These growth marks are similar to the annual rings found in tree trunks, except that in the case of coral, the marks are made daily, in response to the day—night cycle of solar illumination. However, they also show yearly variations as the coral's growth responds to Earth's seasonal changes, allowing us to perceive annual cycles. Coral growing today shows 365 marks per year, but ancient coral shows many more growth deposits per year. Fossilized reefs that are five hundred million years old contain coral with nearly 400 deposits per year of growth.
Why is Earth's spin slowing? The main reason is the tidal effect of the Moon. In reality, the tidal bulge raised in Earth by the Moon does not point directly at the Moon, as was shown in Figure 7.22. Instead, because of the effects of friction, both between the crust and the oceans and within Earth itself, Earth's rotation tends to drag the tidal bulge around with it, causing the bulge to be displaced by a small angle from the Earth—Moon line, in the same direction as Earth's spin (Figure 7.24). The net effect of the Moon's gravitational pull on this slightly offset bulge is to reduce our planet's rotation rate. At the same time, the Moon is spiraling slowly away from Earth, increasing its average distance from our planet by about 4 cm per year.
This process will continue until Earth rotates on its axis at exactly the same rate as the Moon orbits Earth. At that time the Moon will always be above the same point on Earth and will no longer lag behind the bulge it raises. Earth's rotation period will be 47 of our present days, and the distance to the Moon will be 550,000 km (about 43 percent greater than at present). However, this will take a very long time—many billions of years—to occur.



If we get to the point where the moon remains in effective geostationary orbit over the Earth, then that would mean an Earth without almost no daily tides.  There might be some slight tidal force from the Sun, and there would be longer term tidal effects due to variations in the lunar orbit (distance from the Earth, and differences between the axis or rotation of the Earth, which itself is not constant, and the plane of orbit of the moon).



George
« Last Edit: 21/06/2006 15:32:08 by another_someone »
 

Offline tony6789

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Re: Is The Earth Spin Slowing ?
« Reply #2 on: 22/06/2006 19:38:42 »
i thought the earth's spin increaced

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Offline ukmicky

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Re: Is The Earth Spin Slowing ?
« Reply #3 on: 23/06/2006 00:30:53 »
quote:
Originally posted by tony6789

i thought the earth's spin increased

NEVER! underestimate youth

No the spin of the earth is slowing as the distance between the earth and moon is increased
Michael
« Last Edit: 23/06/2006 00:39:16 by ukmicky »
 

Offline tony6789

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Re: Is The Earth Spin Slowing ?
« Reply #4 on: 23/06/2006 15:47:33 »
oh i must have gotten the 2 confused!

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Re: Is The Earth Spin Slowing ?
« Reply #4 on: 23/06/2006 15:47:33 »

 

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