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A really random but simple question about gravity.

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rabidmonkey4262
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28 May 2011, 10:09 pm

naturalplastic wrote:
rabidmonkey4262 wrote:
naturalplastic wrote:
Burzum wrote:
SammichEater wrote:
F = MG

Image

The force of gravity from the sun at the distance of earth is stronger than the force of gravity from the centre of earth at the distance of the earth's surface.

We don't get pulled into the sun because we are in orbit.


Nonsense.

If the earth stopped its forward motion then it would stop orbiting and start plunging toward the sun. But you and I would not fall from the earth toward the sun. We would be stuck like glue to the earth as it and us all plunge into the sun ( except at the last moments tidal forces might tear us from the earth in the last few miles to the sun surface).


The earth is not going forward. The earth is going in an elliptical motion. Any type of forward/backward motion is irrelevant to a spherical object. If the Earth stopped it's orbit, that would only be because the object that it is supposed to orbit around (the sun) disappeared. In which case we'd go shooting off into space, not into a non-existent sun. You just need to look at a force vector diagram of centripetal motion to understand that. The vector pointing to the center (the sun) would disappear and we're only left with the vector pointing out. Image




The earth IS trying to move in a straight line at 40 thousand miles an hour. The sun is trying to pull the earth towards itself through the force of gravity. The gravity and momentum balance out so the earth moves in an orbit around the sun. Thats the whole reason we are in orbit around the sun in the first place!

If you somehow applied brakes to the earth so it stopped its linear motion then there would be nothing to balance the gravitational pull of the sun and the earth would fall into the sun.
And we would stay on its surface for most of the ride and would not fall seperately into the sun.

Thanks for reiterating the very point im making!

But actually something just occured to me- for the wrong reason you might be right.

Okay: on one hand:

The sun is 240,000 times the mass of the earth, but the center of the sun is 25 thousand times farther away from a person on earth than is the center of the earth. Twenty five thousand squared is 625 million.
Divide that number into the 240thousand and you'll find that the pull of the sun on your body is about 1/2500th as strong as that of the earth on your body by that newtonian equation.

But on the other hand:

In its orbit around the Sun the Earth is moving about 40thousand miles an hour. That means that escape velocity from the Sun in our neighborhood of the solar sytem must be slightly more than that speed .
But escape velocity from the earth isself is only 25 thousand miles an hour. So I gotta admit that now Im confused too! Maybe you're right.

One things for sure. The spinningof the earth is irrelevent. But maybe not the orbit of the earth. Like Sarah Palin says "Ill have to get back to you on that". I know that the earth pulls on you more than does the sun, but apparently a rocket has to go faster to move to the outer planets than it has to to just get off the earth. Its a conundrum.


and, you just reiterated what I said. You basically just explained the diagram in your own words. I said what would happen if you take out the centripetal force vector. You said what would happen if we take out the velocity. We're just saying different halves of the same thing.

The spinning of the Earth is very relevant. If the Earth stopped spinning we'd all be whisked away by the still moving atmosphere. It doesn't matter if the Earth and sun are still orbiting, because at that point we're at the mercy of the atmosphere.


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28 May 2011, 10:16 pm

rabidmonkey4262 wrote:
huntedman wrote:
There seems to be allot of confusion in what the original question asked was. The way i read it you are comparing object-earth and object-sun gravity when the object is located at the earth's surface.

object-earth gravity is significantly stronger.
That's definitely a mis-interpretation of the original question. " Is the sun's gravity at the Earth's average distance from the sun stronger or weaker than the Earth's gravity on the surface of the Earth?

Clearly the first part is asking for the gravitational force between the sun and the Earth. The second part is asking about the gravitational pull of an object actually on Earth. People are creating their own question, and then answering it. There is nothing that says anything about object-sun gravitational pull. If that was the question, then the answer would be obvious and quite easy, seeing as we're still on Earth and not flying towards the sun.


I do not see where you get your interpretation, the sun's gravity at the radius of the earth's orbit doesn't imply the second object has to be the earth. Comparing the gravity of two massive objects to one massive object and a human makes no sense and tells you nothing.



Last edited by huntedman on 28 May 2011, 10:24 pm, edited 1 time in total.

rabidmonkey4262
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28 May 2011, 10:22 pm

naturalplastic wrote:
But actually something just occured to me- for the wrong reason you might be right.

Okay: on one hand:

The sun is 240,000 times the mass of the earth, but the center of the sun is 25 thousand times farther away from a person on earth than is the center of the earth. Twenty five thousand squared is 625 million.
Divide that number into the 240thousand and you'll find that the pull of the sun on your body is about 1/2500th as strong as that of the earth on your body by that newtonian equation.
I already did those calculations way way back. Read my first post carefully, and read the original question. We're not concerned with the pull of the sun on your body. That was an incorrect inference that quite alot of people made. Of course the pull of the Earth on your body is much greater. We don't even need to prove that using Newton's equation, and no one would've posted such a silly obvious question in the first place.

We are only concerned about the pull of the sun on Earth as it compares to the pull of an object on Earth. That was what the original question stated. As I said numerous times, the pull of the sun on the Earth is much greater than the pull of an object on Earth. You can check my calculations if you're still in doubt. If the gravitational force of an object on Earth was greater than the pull of the sun on the Earth, then the Earth would be rotating around the object and not the sun. This would need to be a very massive object.


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rabidmonkey4262
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28 May 2011, 10:29 pm

huntedman wrote:
rabidmonkey4262 wrote:
huntedman wrote:
There seems to be allot of confusion in what the original question asked was. The way i read it you are comparing object-earth and object-sun gravity when the object is located at the earth's surface.

object-earth gravity is significantly stronger.
That's definitely a mis-interpretation of the original question. " Is the sun's gravity at the Earth's average distance from the sun stronger or weaker than the Earth's gravity on the surface of the Earth?

Clearly the first part is asking for the gravitational force between the sun and the Earth. The second part is asking about the gravitational pull of an object actually on Earth. People are creating their own question, and then answering it. There is nothing that says anything about object-sun gravitational pull. If that was the question, then the answer would be obvious and quite easy, seeing as we're still on Earth and not flying towards the sun.


I do not see where you get your interpretation, the sun's gravity at the radius of the earth's orbit doesn't imply the second object has to be the earth. Comparing the gravity of two massive objects to one massive object and a human makes no sense and tells you nothing.
If you can't see where I get my interpretation even after highlighting those exact words in the OP, then there's nothing more I can do. As I said before, the original poster would not have asked if the sun exerts a greater force on an object than the Earth. Again, that answer would be very easy, seeing as an object situated on Earth will not be "pulled" toward the sun. That would be a silly and obvious question that doesn't need to be asked.

Also, with either interpretation, it does tell you something. With your interpretation, we simply establish that we're not going to go flying off to the sun (duh!) In my interpretation, I established that the Earth rotates around the sun because of the gravitational pull between the Earth and the sun is greater than the gravitational pull between the Earth and an arbitrary object, as long as that object is under a certain mass. It does make sense and it does tell you something.


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naturalplastic
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29 May 2011, 12:04 am

rabidmonkey4262 wrote:
huntedman wrote:
rabidmonkey4262 wrote:
huntedman wrote:
There seems to be allot of confusion in what the original question asked was. The way i read it you are comparing object-earth and object-sun gravity when the object is located at the earth's surface.

object-earth gravity is significantly stronger.
That's definitely a mis-interpretation of the original question. " Is the sun's gravity at the Earth's average distance from the sun stronger or weaker than the Earth's gravity on the surface of the Earth?

Clearly the first part is asking for the gravitational force between the sun and the Earth. The second part is asking about the gravitational pull of an object actually on Earth. People are creating their own question, and then answering it. There is nothing that says anything about object-sun gravitational pull. If that was the question, then the answer would be obvious and quite easy, seeing as we're still on Earth and not flying towards the sun.


I do not see where you get your interpretation, the sun's gravity at the radius of the earth's orbit doesn't imply the second object has to be the earth. Comparing the gravity of two massive objects to one massive object and a human makes no sense and tells you nothing.
If you can't see where I get my interpretation even after highlighting those exact words in the OP, then there's nothing more I can do. As I said before, the original poster would not have asked if the sun exerts a greater force on an object than the Earth. Again, that answer would be very easy, seeing as an object situated on Earth will not be "pulled" toward the sun. That would be a silly and obvious question that doesn't need to be asked.

Also, with either interpretation, it does tell you something. With your interpretation, we simply establish that we're not going to go flying off to the sun (duh!) In my interpretation, I established that the Earth rotates around the sun because of the gravitational pull between the Earth and the sun is greater than the gravitational pull between the Earth and an arbitrary object, as long as that object is under a certain mass. It does make sense and it does tell you something.


The OP asked "is the sun's gravity at the earths avg. distance from the sun stronger or weaker than the earths gravity is on the surface of the earth."


He's comparing the influence of the earth's gravitational field to the influence of the sun's gravitational field at our distance from the Sun. Pure and simple. He didnt say anything about any "third object".

Your interpretation of the question is dead wrong. Everyone else is correct. Cut out the comedy.

He IS setting up a tug of war between the sun and the earth over objects on the earth's surface ( exactly what you're saying he is NOT doing).

Okay, lets treat you mangled version of his question as a seperate question.

First you ought to rephrase it into more vivid terms. Like "how massive does an object on earth have to be for it to exert the same gravitional pull on a person as does the sun- assuming that the person is standing on top of the object?"

Answer it when its phrased that way.



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29 May 2011, 4:06 pm

naturalplastic wrote:

The OP asked "is the sun's gravity at the earths avg. distance from the sun stronger or weaker than the earths gravity is on the surface of the earth."


He's comparing the influence of the earth's gravitational field to the influence of the sun's gravitational field at our distance from the Sun. Pure and simple. He didnt say anything about any "third object".

Your interpretation of the question is dead wrong. Everyone else is correct. Cut out the comedy.

He IS setting up a tug of war between the sun and the earth over objects on the earth's surface ( exactly what you're saying he is NOT doing).

Okay, lets treat you mangled version of his question as a seperate question.

First you ought to rephrase it into more vivid terms. Like "how massive does an object on earth have to be for it to exert the same gravitional pull on a person as does the sun- assuming that the person is standing on top of the object?"

Answer it when its phrased that way.


Let's say the object in question is the moon. In that case, the suns gravity is still stronger.

You might want to take a look at this.

http://in.answers.yahoo.com/question/in ... 812AAq4kPA


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29 May 2011, 5:03 pm

The question as phrased contains too many undefined terms, and as such is unanswerable. Please define: are you referring to the effect of Solar gravity on an object in deep space that happens to share an orbit (although not an orbital position) with Earth, an object orbiting Earth, or an object on the surface of Earth? Or do you wish to compare Solar gravity on Earth to terrestrial gravity on an object on Earth's surface?

Please define your terms more clearly when asking scientific questions; otherwise, we come across sounding as confused as a climatologist testifying before Congress (and for the same reasons).


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30 May 2011, 9:36 am

Not a science expert, but my 2 cents.

Gravity is somewhat a matter of relativity. The earth, and all other planets, orbit the sun at that "sweet spot" where the sun's pull isn't enough to overcome the orbital velocity of the planet. Upset that balance and the planet either flies out of the system or spirals into the sun.

Likewise, gravity seems to have a relativistic effect based on proximity.

A black hole's "pull" diminishes as you get farther from it. As light supposedly can not escape from the pull of a black hole, if the pull was a constant, then at any distance objects would be drawn to the black hole. This, in fact, might actually happen, but the farther away, the slower it happens. Light moves so fast that X distance away it is pretty much unaffected by the gravity well.

Hence, inner planets orbit very fast. Outer planets orbit very slow.

Likewise, a large inner planet would have to orbit faster than a smaller inner planet the same distance from the sun as the effect on the larger body would be more pronounced.

So, all bodies in space influence bodies close to them. There is a range at which the local gravity well is dominant and nothing else can really influence what's in its range. Exit this and maybe another gravity well can affect you. Probes, satellite, rockets, etc. are not affected by the sun once leaving earth's gravity because they are so small by comparison to a planetary body that they don't need much velocity to overcome the sun's gravitational pull....just as a probe can skim the upmost levels of a gas giant's atmosphere and still keep on going where a small moon would be pulled in at the same speeds.



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30 May 2011, 2:54 pm

The earth orbits the sun in an eclipse. During the northern hemisphere winter the earth approaches closest to the sun (perihelion) so it speeds up to compensate. During the northern hemisphere summer it is at its furtherest distance (aphelion) it slows down as the suns gravity pulls it back again. This speeding up and slowing down occurs because of the elliptical orbit. Therefore the gravitational pull is strongest at perihelion and weakest at aphelion.



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30 May 2011, 4:13 pm

SammichEater wrote:
naturalplastic wrote:

The OP asked "is the sun's gravity at the earths avg. distance from the sun stronger or weaker than the earths gravity is on the surface of the earth."


He's comparing the influence of the earth's gravitational field to the influence of the sun's gravitational field at our distance from the Sun. Pure and simple. He didnt say anything about any "third object".

Your interpretation of the question is dead wrong. Everyone else is correct. Cut out the comedy.

He IS setting up a tug of war between the sun and the earth over objects on the earth's surface ( exactly what you're saying he is NOT doing).

Okay, lets treat you mangled version of his question as a seperate question.

First you ought to rephrase it into more vivid terms. Like "how massive does an object on earth have to be for it to exert the same gravitional pull on a person as does the sun- assuming that the person is standing on top of the object?"

Answer it when its phrased that way.


Let's say the object in question is the moon. In that case, the suns gravity is still stronger.

You might want to take a look at this.

http://in.answers.yahoo.com/question/in ... 812AAq4kPA


That is interesting.
Okay. So how massive would the moon have to be to equal the sun in its gravitational effect on the earth if the moon were to stay at its present distance?

Using the inverse square law- the sun is 400 times the distance from us as the moon. but the sun is about 2 million times as massive as the moon. So 400 squared is 160 thousand- divide that into two million and you get about eight percent. The moon has eight percent of the gravitonal pull on the earth as does the sun (even though the moon effects the tides on earth more than does the sun-explain THAT). So the moon would have to be 12.5 times as massive as it is now to have the same gravitational pull on us as does the sun( ie to turn tht eight percent into a hundred percent). The moon would still be much smaller than the earth but it would have to bulk up to being about the same size as Mars to exert the kinda gravitational pull on your body from its present distance of 238,000 miles as does the sun at its distance of 93 million miles.



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09 Jun 2011, 1:53 am

http://en.wikipedia.org/wiki/Newton%27s ... ravitation

inverse-square laws, in which force is inversely proportional to the square of the distance between the bodies.

That's all that needed to be said.



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09 Jun 2011, 12:03 pm

What body do you fall towards - the earth or the sun?


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09 Jun 2011, 12:07 pm

SammichEater wrote:
Definitely earth's gravity, or we would all be falling towards the sun and not the earth. But maybe not, because the earth is in orbit around the sun, and we are not in orbit around the earth.


Orbits are caused by the collective force of the central body's gravitational pull on the orbiting body and the orbiting body's inertia. This inertia is what prevents the orbiting body from falling. We are not orbiting around the earth because we are already on the earth; there is no inertia pushing us through space.


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09 Jun 2011, 12:07 pm

LordoftheMonkeys wrote:
What body do you fall towards - the earth or the sun?


Both. You free fall toward the Earth until the ground stops you. The Earth falls around the Sun and nothing is stopping it.

ruveyn



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10 Jun 2011, 2:33 am

ruveyn wrote:
LordoftheMonkeys wrote:
What body do you fall towards - the earth or the sun?


Both. You free fall toward the Earth until the ground stops you. The Earth falls around the Sun and nothing is stopping it.

ruveyn


It's being pulled in a little all the time, but the effects are so subtle we tend to ignore them. It will take longer than the life of the solar system for the Earth to fall "into" the sun, but it's always "falling inward". We are actually still falling towards the center of the earth, but as you point out, the ground stops us from physically falling, but we're still always being pulled in.



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06 Jul 2011, 4:20 am

TheKingsRaven wrote:
Just a quick question: Is the sun's gravity at the Earth's average distance from the sun stronger or weaker than the Earth's gravity on the surface of the Earth?


Earth's gravity on surface: 9.8 m/s2
Sun's gravity on earth surface: 0.00593 m/s2