the moon

[DutchE]

i asked nasa "did the moon ever spin, if so, when did it stop?". they said "it did spin and stopped 200 million to 2 billion years ago." i don't think so. what do you think?

[Duke]

The moon does spin. its 'years' are the same length as its days. This means we always see the same side of the moon. It may has spinned faster at one point though.

[VendingMenace]

it most likely did spin faster at one time, however, it was slowed to where it is today due to tidal forces.

 

We all know that the moon exibits tidal forces on the earth, and that the liquid parts of the earth bulge on the sides of the earth that are nearest and farthest away from the moon. That is why we get tides. Of course this is a two way street, the moon also feels tidal forces from the earth, only to a much greater extent.

 

Also, the moon is not quite a consistant ball of mass, there are areas of the moon that are more dense than others. These "heavier" areas tend to be pulled on harder by the earth's gravity. As such, these areas tend to "want" to be closer to the earth. Now, it just so happens there is a large section of the moon that has a highly dense area in it. The moon, at one time, used to spin faster than it does now. However, over time the tidal forces of the earth slowed down the moon's rotation by pulling harder on this more dense area. Over many many years, the moon's rotation slowed to the point it is at today, that is it is slowed to the point where this heavier part is always facing the earth. That is why the moon rotates on it own axis is such a way that the same side is aways facing us, it is becuase this is the "heavier" side of the moon.

 

Now, by the same token, the moon is slowly slowing down the rotation of the earth. In another so many years, the earth will also slow to the point that the same side of the earth is aways facing the moon. It is just that the forces exerted by the moon on the earth is much less than the force exerted by the earth on the moon, so it is taking the moon much longer to slow down the earth. cool

[DutchE]

it doesn't spin, it rotates. that means it turns it's back on the sun every month (rotate) but it doesn't spin. but when did it stop?

[VendingMenace]

it doesn't spin, it rotates.

 

Actually, it does spin. I promise. If the moon didn't spin, then we would see different sides of the moon. However, we don't. We only see one side of the moon, the only way this could happpen is if the moon spins on its axis while it also rotates around the earth.

 

If you don't belive me, then try it for yourself. Get a tennis ball or some other shere. Mark a point somewhere on this sphere. Now get abother object, a soda can or something. Now move the tennis ball around the soda can in a cirle, making sure the spot you made on the tennis ball is aways facing the can. You will find that in order to do this you will have to make the ball rotate around its own axis (what we call "spinning"). Conversely, if you move teh ball around the can in a circle without spinning the ball you will find that the spot does not always face the can.

 

SO, by doing this simple expreiemnt you will see that the moon does indeed rotate, as it must if we are to always see only one side of it from earth.

 

but when did it stop?

 

well, if nasa told you 200 million to 2 billion years ago, then i am inclined to belive them.

[swansont]

VendingMenace said in post #3 :

We all know that the moon exibits tidal forces on the earth, and that the liquid parts of the earth bulge on the sides of the earth that are nearest and farthest away from the moon.

 

The solid parts, too. But since the liquid parts are more free to move about, we see the water tides. But the solid parts move by about 30-50 cm each day.

[bigjnorman]

he he, my father swears that if you dig a hole in the ground while the moon is in its waining phase and try to fill it with the dirt that was removed from the hole during the waxing phase, you will not have enough dirt (or more dirt, i can't remember).

 

It would seem possible, although I would think it would be more of a result from daily tidal forces than from monthly whatever forces

[atinymonkey]

Um, is your garden covered with holes by any chance?

[VendingMenace]

The solid parts, too. But since the liquid parts are more free to move about, we see the water tides. But the solid parts move by about 30-50 cm each day.

 

yeah, i thought about mentioning this too, but really it is the same thing. The solid parts (like the crust) bulge due to the liquid parts underneath them (the mantle) moving in respnse to the tidal forces and applying pressure. I am not sure that the tidal effects on a solid earth would be even as great as the appear to be now, if the earth was not liquid on the interior. I guess if we knew how much the moon bulges now, we would know the answer

[DutchE]

VendingMenace said in post #3 :

liquid parts of the earth bulge on the sides of the earth that are nearest and farthest away from the moon cool

 

i got a tidal predictor and looked at tides at a time of full moon (on the gm line). it wasn't actually high but it was low. therefore i think not high, but low tides point at the moon.

[swansont]

VendingMenace said in post #9 :

The solid parts (like the crust) bulge due to the liquid parts underneath them (the mantle) moving in respnse to the tidal forces and applying pressure. I am not sure that the tidal effects on a solid earth would be even as great as the appear to be now, if the earth was not liquid on the interior. I guess if we knew how much the moon bulges now, we would know the answer

 

This sounds suspicious. If the crust was going to move due to the pressure exerted by the underlying liquid, why can't it move due to the direct tidal force?

[YT2095]

it is awafully good timing on the moons part tho! beats me how it times so excellently with it`s rotation/spin (means the same to me). I recon it maybe something to do with "natural resonance", same thing can be observed in the Lab with very simple apparatus, swinging pendelum clocks on the same shelf at opposite ends with a pendelum out of phase will synch itself to the other in perfect phase and more astonishingly REMAIN that way! after a short period of time! Damned wonderfull and amazing this Universe is that we are all given to look at!

[Kedas]

The right question would be like YT2095 suggested:

Are some moon rotation speeds more stable than others?

[VendingMenace]

This sounds suspicious. If the crust was going to move due to the pressure exerted by the underlying liquid, why can't it move due to the direct tidal force?

 

Well, the crust probably does move due to direct tidal forces, it is just that this movement is negligable compared to the movement due to the liquid underneath it.

 

Perhaps it will help to think about a balloon filled with water. You could try to pull directly on the rubber of hte balloon and change its shape that way. However, if you just cause the water to shift about to one side (like squeezing the balloon or something) then the water will force the balloon to change shapes.

 

Perehaps this is not the best analogy. So instead, lets assume that we have two balloons, one has a neutral liquid inside of it, but the rubber carries a charge on it. The other balloon is made of neutral rubber, but the liquid inside of it is charged. Now, the total charge on the balloon and the liquid are the same. You apply a electric feild to both balloons, which one has its shape distorted more? I don't really know, but that is something to think about.

 

In conclusion, i think that the tidal forces do affect the crust directly, but the affects of these forces on the liquid underneath the crust are more substantial, both becuase there is more mass in the liquid and becuase it is more efficient to have the liquid force the crust to move than to have the crust move directly. But i am just kinda shooting in the dark here and i could be wrong

[Glider]

YT2095 said in post #12 :

it is awafully good timing on the moons part tho! beats me how it times so excellently with it`s rotation/spin (means the same to me). I recon it maybe something to do with "natural resonance", same thing can be observed in the Lab with very simple apparatus, swinging pendelum clocks on the same shelf at opposite ends with a pendelum out of phase will synch itself to the other in perfect phase and more astonishingly REMAIN that way! after a short period of time! Damned wonderfull and amazing this Universe is that we are all given to look at!

 

Strangely enough, women do that too.

[alt_f13]

And people walking next to each other.

 

I find the thing about women and the cycles of the moon kinda romantic, in the poem sense, if you get me.  In a kind of heartbeat of the earth sort of way.