The Moon

John_C

If the moon pulls the tides around and energy can be extracted by the tides then is the moon loosing energy? Can we expect it to crash into the Earth at some stage?

slade_x

John_C wrote:

If the moon pulls the tides around and energy can be extracted by the tides then is the moon loosing energy? Can we expect it to crash into the Earth at some stage?

part of your question is a bit hard to understand... "energy can be extracted by the tides"

But the moon is not in a decaying orbit, in fact its moving away from earth
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The Earth exerts a tidal force on the moon which tends to strecth it out along the line joining the Moon and Earth. This create "tidal" bulges. When the moon was rotating faster, different parts of the moon would pass through these tidal bulges, this created a friction which caused the moon to slow its rotation until it reached the state it is now in. This is known as being in tidal lock.

The Earth undergoes the same with the Sun, But for the Earth, this is only part of the picture. The Moon also creates tidal bulges on the Earth, and because of the proximity of the Moon these are larger than those of the Sun,

This causes two things to happen; One, the Earth slows in its rotation, and two, the Earth tends to drag the tidal bulges along with its rotation.

The draging of the tidal bulges pulls them slightly out of alignment with the moon, Causing a "forward" pull on the Moon, The Earth transfers some of its rotational energy to the moon. Adding Energy to the Moon causes it to move into a higher orbit. This will continue until the Earth rotates at the same rate as the moon orbits.

If the moon orbited the Earth in the opposite direction than the Earth rotated, this mis-alignment would pull counter to its orbital direction, the Moon would fall into a lower and lower orbit.

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Besides even in the case of a moon in a decaying orbit like say phobos.. its speculated to collide with Mars within the next few tens of millions of years, so i wouldnt worry about it..

Our sun may very well die before any natural disaster destroys earth..

although it is said that our solar system will pass through a region of space that can potentially destroy all life on earth, as it is speculated that it has happened before in prehistoric times.. another thing you wont have to worry about in your lifetime

spinalsly

slade_x wrote:

part of your question is a bit hard to understand... "energy can be extracted by the tides"

im not sure if this is what u did not understand but look.......

http://www.darvill.clara.net/altenerg/tidal.htm

slade_x

spinalsly wrote:

im not sure if this is what u did not understand but look.......

http://www.darvill.clara.net/altenerg/tidal.htm

Oh right, i was thinking that but was wondering why us using hydro powered turbines would be a drain on the moon

John_C

slade_x wrote:

the Earth slows in its rotation

That's my answer, Thank you.

Question number 2.
If the earth's rotation is slowing, how much is it slowing by and can we expect a longer stretch in the evenings any time soon?

slade_x

John_C wrote:

That's my answer, Thank you.

Question number 2.
If the earth's rotation is slowing, how much is it slowing by and can we expect a longer stretch in the evenings any time soon?

I would doubt it "any time soon", this would all happen over a very very very long period of time...

were probably talking about a few seconds for every few 100 thousand years

Earth in essence would be slowing down to sync with the moon.. as for every 1 revolution of the moon the earth revolves 27 or so times... it could take a "very" long time.. the human race wil more than likely be extinct by the time anyone could even chronographically time the difference and notice a minor change

EDIT: update.. i went looking around and came across this site

From more than halfway down the page:

How Long Has the Moon Been Receding?
Friction by the tides is slowing the earth’s rotation, so the length of a day is increasing by 0.002 seconds per century. This means that the earth is losing angular momentum.[7] The Law of Conservation of Angular Momentum says that the angular momentum the earth loses must be gained by the moon. Thus the moon is slowly receding from Earth at about 4 cm (1½ inches) per year, and the rate would have been greater in the past. The moon could never have been closer than 18,400 km (11,500 miles), known as the Roche Limit, because Earth’s tidal forces (i.e., the result of different gravitational forces on different parts of the moon) would have shattered it. But even if the moon had started receding from being in contact with the earth, it would have taken only 1.37 billion years to reach its present distance.[8] NB: this is the maximum possible age—far too young for evolution (and much younger than the radiometric ‘dates’ assigned to moon rocks)—not the actual age.

Of course with our current level of technology and knowledge of physics all science is purely speculation. and always will be, its science :rolleyes: