Gravity Effect of Moon

Discussion in 'After Hours Lounge (Off Topic)' started by DaveSarcevic, Jul 20, 2004.

1. DaveSarcevic Agent

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Today being the 35th anniversary of the landing on the moon, got me thinking about the orbit of the moon. As the moon orbits the earth the same side always faces the earth. My question for you astronomy buffs out there is: if the moon rotated on it's axis say once every 8 hours. Would there be a difference of the gravitational effect of the moon on earth than what it is now. I know that gravity is proportional to the mass and density of an object.

2. Christ Reynolds Producer

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i'm no astronomy buff, but i'd say that there would be no change, as long as the distance between the earth and moon would be the same. i guess the only distance would be that the moon isnt completely round, it may weigh a little more on one side than another as it rotates, due to craters and such, but this would have very little effect. the equation for gravitational force is

F=G(M*m/r^2)

where G is the gravitational constant 6.67 x 10-11 N(m2/kg2). anyway, if everything in the equation stayed the same, the gravitational force wouldnt change.

CJ

3. BrianW Cinematographer

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There would be a very slight difference due mostly to tidal forces but also, to a much lesser degree, a phenomenon known as frame dragging.

It's no coincidence that the Moon has only one face turned toward us. More to the point, it didn't used to be this way. Lunar tides (i.e., tidal forces on the Moon, not oceanic tides on Earth) and frame dragging slowly transfer the angular momentum from the Moon's rotation about its own axis to its orbit around the Earth. This occurs until the Moon no longer spins in the sky relative to Earth, or until the Moon is stuck with one side always facing Earth.

This has already happened with the Moon relative to Earth, and the flip side of that coin is that it is also happening with the Earth relative to the Moon. In other words, the time will eventually come when the Earth will have one side always facing the Moon!

Imagine half the world never having the Moon in its sky. But the other half of the world won't have much to brag about. The Moon will be so far away by then that it won't even be nearly as large as it is now. Total solar eclipses will be a thing of the past. Climate changes will be more severe without the Moon's stabilizing influence on the Earth's own spin. And the day will be so long that you will be able to sleep in for twelve hours and still make it to work on time to put in a forty-hour work day.

But in our daily lives, everything else being equal, a Moon that spins in the sky above us would make no difference. The biggest difference I can imagine would be that we would need to add leap-seconds more frequently to our calendar to account for the slightly accelerated decrease in the Earth's spin.

4. Scott Merryfield Executive Producer

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Property values on the far side of the moon would be higher because they would have a view of the earth.

5. JamesCB Second Unit

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"There's no dark side of the Moon really. As a matter of fact, it's all dark." -P.F.

6. Julie K Screenwriter

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Half the moon is always dark.

It's just not always on the far side of the moon, however.

7. Grant B Producer

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Maybe it's like the refirgerator light....sure it's on when you open the door.....
Whenever we look at the darkside of the Moon; they turn off the lights. We have to catch them dammit!

8. Greg*go Supporting Actor

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Back when I was a kid, there was only 1 side to the moon. And that was more then enough for everybody.

Kids today.

Some here might find this funny: Proof the Moon Does not Exist There is a reward for anyone who can prove otherwise on the site, at least that what it says anyway.

9. Jack Briggs Executive Producer

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I hope people here understand just what it is that Julie said. It's very subtle, and very correct.

The Moon rotates on its axis in approximately the same time it takes it to orbit Earth. As Brian suggests, if the Moon were rotating on its axis in just eight hours the effect on Earth would be minimal.

10. Julie K Screenwriter

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Wow, what solid proof that no-moon guy has!

(At least he's far more entertaining than the moon landing hoax folks are.)

BTW, I've seen the dark side of the moon many, many times....

11. Christ Reynolds Producer

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i love listening to these types of people who try to talk about how we never landed on the moon, so the "no moon at all" guy should be a real treat.

CJ

12. MarkHastings Executive Producer

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Freaky! Last night I was thinking about posting a thread about the moons gravitational pull on the Earth.

Basically, I was gonna say that I notice my weight is usually 3-4 pounds lighter in the morning than at night. I figured maybe it was because I wasn't full in the morning? but I was also wondering if it had anything to do with the pull of the moon?

Is it true that there is a big difference on the gravitational pull? I mean, enough to cause a 3-4 pound difference throughout the day?

13. Grant B Producer

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I just watched this program on Discovery on how they are finding more and more orbits sync up on the planets they discover ...

14. Greg*go Supporting Actor

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The no moon guy is a real treat. He has a whole website dedicated to stupid stuff like that, that's one of the more funny ones though. I just hope it's all a joke, and nothing he takes seriously.

Mark,
I doubt the moon has much impact on your weight throughout the day. Since it happens in the morning should be proof of that, since the moon is in different places in earth's orbit throughout the days of the year. Maybe your body just burns off a lot of weight at night. Are you doing the horizontal dance or something before calling it a night... wink wink, nudge nudge? I find my body weight changes 3-5 at any given time throughout the day too. It might be normal, how many people do you know that weigh themselves more then once a day anyway?

GrantB,
I'm afraid I missed that episode. What planets are you talking about them discovering?.

15. MarkHastings Executive Producer

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Well, it's good to hear that it happens to someone else. I figured it had to do with burning off (at night) all that I ate during the day, but the gravitational pull seemed like it might have been a possibility.

16. Marc_Sulinski Supporting Actor

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A lot of the weight that you lose at night comes from loss of water from the body. You lose water by exhaling it in the form of water vapor.

17. BrianW Cinematographer

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You also exhale carbon, but I don't think it could possibly be three pound's worth in a single night, though I really have no idea about things like that.

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