If the moon stopped moving, would it crash into the earth?

It doesn’t work like that.

You need to clarify. By “stop moving,” do you mean…

1) It would cease to rotate on its axis? Then no.
2) Its angular momentum would become zero? Then yes.

Yea I don’t think it does either.

I see that one of your areas of expertise is “science.” It is not cool to have us do your research; however here’s a start. Three-body problem (and I’m not talking Paris Hilton and Co.)

I would say ‘expertise’ is pushing it a bit, i did english at uni and am not in a science related job, it’s just something im really interested in, although obviously don’t know much at all…

By stop moving I meant, did it have to, at some point, be travelling past the earth to start orbiting, and if so, could it ever lose momentum?

Presumably, it IS losing momentum, ever so slowly, as the “vacuum” of space still is not an absolute vacuum. There are particles out there, no matter how sparse, and they are impeding the moon’s revolution around earth, and thus, are reducing its angular momentum. There will EVENTUALLY be a time when the moon isn’t revolving quickly enough to sustain its orbit, and the two will collide. But probably not for billions of years.

I just watched something on Natgeo? Discovery? about the creation of the moon. The moon is actually receding by a few centimeters every year.

Here is the popular theory or belief:

The earth is rotating slower due to tidal friction, as a balance, the moon is accelerating and its orbit is increasing. Eventually, moon’s orbit would be 50% larger than it is now, and the moon and the earth will be facing each other with one side only, and pretty much “locked” together.

Are you terrified yet?

I wonder which side of the Earth would get the moon view.
Better get in on the real estate market there early.
you know, sometime in the next few hundred thousand ears, or so

@fireside, I hear ya on that one!

typo lols

Also, the moon was not “traveling past” the earth before it began orbiting. The moon was formed very early in Earth’s history (way way way before dinosaurs or even amoebas), when another large object hit the earth. The impact sent up a huge cloud of dust and rock around the earth. Most of it settled back down to the earth’s surface, but some of it began to gravitationally coalesce into another object—the moon. After a few million years, the moon was formed!

To answer the question, gravity keeps the moon in orbit around the earth. If gravity were to disappear the moon would stop accelerating, ie orbiting. It would continue in a straight line on its most recent trajectory, flying off into the solar system. If, however, gravity were suddnely much stronger, the moon would begin to creep closer to the earth, spiraling in until impact.

The only thing that could possibly create a scenario like you envision is if a VERY large object (another moon) were to crash head-on into our moon. It would then lose much of its angular momentum and fall towards the earth. However, the collision would probably destroy the moon as we know it and send the pieces flying in lots of different directions, so who knows what the result would be.

From NASA…

The secular change in the planet’s rotation is a classical topic in geophysics. It goes back some 300 years to when Sir Edmond Halley first hypothesized that the moon was accelerating in its orbit. Most of Halley’s lunar acceleration was only apparent. It was actually the earth’s rotation slowing down, making the moon appear to accelerate. The moon does accelerate (strictly, it decelerates), but the larger effect is the earth’s rotational braking. This braking is caused by tidal friction. Throughout the earth’s history tidal braking has played, and it will continue to play, a dominant role in the rotation. Currently the secular change in the rotation rate increases the length of day by some 2.3 milliseconds per day per century.

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—Note: the physics use of accelerate which includes negative values (i.e. the moon is decelerating in its orbit).—

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< < lurves Fluther for the impromptu self-education opportunities.

@Rob; It only counts if you can ace the pop quiz without Google. I don’t think I could. I have learned almost too much new stuff here. Brain exposion is imminent.

Aye for tonedef.
As NASA learned, the ability to make an object hold an orbit is a function of the balance between object momentum and gravitational pull. Too much momentum and the satellite keeps moving away, too little and gravity sucks it in.

BTW, if you do notice this phenomenon, please keep us posted.

It would be a possibility yes, it happened once before remember? When the earth was a proto-planet. However, I think it really depends on the calculus, how it stops, where in earth’s rotation around the sun (elliptical orbit remember), and I would think that the chances of it hitting earth again are pretty slim to none. It hasn’t happened in a couple billion years. Anyway, the earth is 50x the size of the moon, that means there is very little chance that if the moon stopped either it’s rotation around the earth or on it’s axis, there is again a heck of a slim chance of it hitting earth.