Sun-Earth-Moon Gravity

Before "we" answer your question, is this this out of your curiosity or is this part of a homework?P.S. The answer is more obvious than you think.

While other people have certainly answered your question, permit me to present it in what I think as a more understandable approach.In space, as long as any two objects have mass and are close enough to each other so that their graviational influence could be felt, you can bet that they orbit each other. More accurately, though, you would have to say that they orbit a point in space between them known as the center of mass between the two objects.Believe it or not, since the Earth has mass, there is a center of mass (or center of gravity) between the Earth and the Sun that is not at the center of the Sun. But because the Sun's mass is considerably greater than the Earth's, the center of mass of the Earth-Sun system is at a point in space that is not at the center of the Sun but beneath its surface.In physics, or at least classical mechanics, you have to view everything in terms of a classical system of objects. If you haven't gone over center of mass (or center of gravity), you will later in your course.And as such, the Earth and the Moon represents a classical system where both objects orbit around the center of gravity between the two. Because the Earth's mass is considerably greater than the Moon, the center of gravity of this system is closer toward the Earth than the Moon, which gives the impression of the moon orbiting the Earth.Because there exists two primary objects in the vicinity of Earth (Earth and Moon), we have to temperarily consider the Earth and the Moon as one object whose center of mass representing the center of this object. Let's call this imaginary object EM. The Sun is another object. Objects EM and the Sun make up another classical system where the center of gravity of this system lies underneath the surface of the Sun (and in fact very very close to the center of the Sun).Ok, perhaps this explanation isn't as easy to digest as I originally thought, but I think it gives a better outline of what is happening here in regard to Sun-Earth-Moon relationship.Hope that helps.Added by edit.Further thought on what I have gone through.Because we can view everything in space in terms of classical systems, we have been able to use this very simple concept to find extra-solar planets. What these planet hunters do is observe a particular star night after night to see if it wobbles. The wobbling of a star indicates that it is orbiting around a center of gravity that lies underneath its surface but is not at its center. In other words, there must be another object of significant mass in close proximity for the star to behave that way.Unfortunately, our current technology can only permit us to confirm a wobble of a star to a certain degree that the companion object (planet) of the star has to be at least as massive as Jupiter. Anything smaller and the wobbling would not be detected at all by our instruments.Anyway, through this very simple concept, we have been able to detect dozens of jupiter size and more massive planets orbiting other stars. Edited by gasby, : No reason given.

You are still not thinking in terms of classical systems. While the Moon and Earth are locked in orbit around their center of gravity, you have to treat the two objects as one when you add the Sun into the equations.Just try to think of it like this. The Earth and the Moon together makes up one system (EM system). Now, think of EM as a single object. EM and the Sun makes up another system.

G*M*m
--------- = F
d*dG = universal gravitational constant
M = mass of one object in Kg
m = mass of the other object
d = distance between them in Meters
F = force in Newton

Time for a little review.Gravitational force between Earth and Sun: 3.52e22 N
Gravitational force between Moon and Sun: 4.33e20 N
Gravitational force between Earth and Moon: 1.98e20 NYour calculation appears to be off. It is not wrong to seperate the two. It is, however, easier for you to understand if you don't seperate the two.You are still new to physics, so it is fine not fully grasp the picture. Give it a little time and I'm sure all will be well P.S. "Alot" means to distribute fractions of something to people while "A LOT" (with a space in between) is the same as "many".

Correct. Some do. Some do, but in most cases the orbits had been too unstable to maintain itself for long... if they existed in the first place.You have to understand that when we are including a massive object of some kind the closer to the object the more perturbations in the gravitational field there are.For example, a small object might be able to orbit Ganymede. However, because of Ganymede's close proximity to Jupiter, pertubations in Jupiter's gravitational field would be tugging the small object until the orbit becomes unstable enough for the object to leave Ganymede. In fact, off the top of my head I can't think of any example of a sat orbiting a sat. Perhaps someone here could point out an example.

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This reminds me of the good ole days when I had to actually drop a bowling ball and a tennis ball at the same time from the top of a ladder in the lecture room to prove to some that heavier stuff don't fall faster. You'd think that even English majors would know this much about gravitation

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Aside from cavediver's answer, my personal opinion is that our current understanding of how the forces of nature work is still vastly incomplete. Therefore, any attempt at answering a question that deals with the universe as a whole should be taken with at least a hint of skepticism. After all, the classical physicists thought they had it all figured out until something like the ultra-violet catastrophe came along.

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I was gonna point this out like 20 minutes ago but reconsidered because I don't like being nitpicked on and certaintly wouldn't want to nitpick other people. But now that someone's done it for me, might as well get the rest out of my system. A few minor nitpics Should be "angular", not circular.There is no such thing as a "linear orbit".No such thing as a circular or "angular" force (at least not how you are defining it). All gravitational forces pull other objects toward the centers of the sources of the forces. The word "orbit" should be used here.

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Somehow, you translated "my personal opinion is that our current understanding of how the forces of nature work is still vastly incomplete" into "my personal opinion is that we shouldn't even try to understand the forces of nature..."What's wrong with having some reservations? There was no error behind the catastrophe. The classical model was just inadequate to explain the observation at the time and so eventually another model came along (QM) that could explain it. Again, the cautious me says that we're bound to run into problems later on that may need to move onto a new model.Don't get me wrong, I'm not saying at all what you thought I was saying. Remember that I was talking to someone who obviously did not have even the basics down. The typical questions that we usually get from someone like that usually reveal that they expect science to take the same approach to the questions as religious doctrines. I just wanted to make sure that he knows science isn't about "this is the truth and all others are false..."Anyway, have you had a couple of drinks?

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There's a reason why I said "my personal opinion". It means take it or leave it and it means absolutely zip if trying to apply it to real science. It was just the skeptic in me talking. Point taken. Well, I'd understand your defensiveness if I proclaimed my words to be the truth of all truths in science. Again, there's a reason why I said "my personal opinion". I was just trying let him know that scientific models aren't treated as doctrines and that healthy skepticism is encouraged.Again, I have run across too many people that think scientific theories and models are equivilent to doctrines in religion. The last thing I want is for them to get an impression that the answers we give is equivalent to the 10 commandments.

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Um, no. That's not the reason why the moon is orbiting the earth. In fact, that's not even true. The gravitational force between the moon and sun is stronger than gravitational force between earth and moon. Actually, that's not the reason why the moon doesn't appear to have its own independent orbit. If mars is close to earth, the two planets would be orbiting each other.But if you look at the path of the moon around the sun and completely ignore that the earth is there, you'd see that the moon does indeed orbit around the sun.So, the question "why doesn't the moon orbit the sun?" makes no sense. Why? Because the moon does orbit the sun.

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Disclaimer:

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Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.

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He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!

Point taken.Well, I guess sometimes the bleedingly obvious needs to be pointed out.Anyway, I'm still right and you're still wrong

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We are BOG. Resistance is voltage over current.

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Disclaimer:

​

Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.

​

He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!

Um, the smilie with the tongue sticking out usually means it's a joke.But to be fair, your answer doesn't really address the question in the original post. Originally, the question is "why doesn't the moon orbit the sun?" Well, the answer is "you moron, the moon does orbit the sun."

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We are BOG. Resistance is voltage over current.

​

Disclaimer:

​

Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.

​

He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!

Well, not really. This is a problem that I often had to face while trying to explain to my students about orbital mechanics. When the person asked why doesn't the moon just leave its current orbit and have an orbit of its own around the sun, the person isn't really thinking about tidal forces and such. The person who wrote the OP had a very common misconception about how gravity works.To give you an extreme example of this misconception, a while back there was a kid that thought he could disprove the theory of gravity all together by pointing out that rocks don't orbit mountains and that astronauts don't orbit the space shuttles. The misconception about gravity is that the smaller object must orbit the bigger object. It's a very simple (and wrong) view of gravity. This is why I always tried to stress the fact that you have to look at these things as systems rather than single objects.The earth-moon is a system. The earth orbits the center of gravity of earth-moon and the moon orbits around the center of gravity of earth-moon. The point of center of gravity of this system in turn orbits around the center of gravity between earthmoon-sun system. Because the sun is so much more massive than the earth and the moon, the center of gravity in this particular system is very very close to the center of the sun.What I'm trying to say in too many words is that we need to recognize the misconception behind the question. Without understanding why, the person who wrote the OP thought that smaller objects must orbit bigger objects. This misconception must be addressed first before we can assume that the person actually was referring to tidal forces. Well... I tend to get nervous everytime the words "scientific explanation" are used, especially when we often have to talk to people who believe science to be just another religious doctrine.

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We are BOG. Resistance is voltage over current.

​

Disclaimer:

​

Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.

​

He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!