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4.5 Billion Orbits? How?


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#1 AFJ

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Posted 23 January 2010 - 10:14 PM

One of the most perplexing questions to me, if I bought into the modern cosmological age of the universe, is how did the earth not migrate into the sun, or fly off into space by now. Four and half billion orbits is simply past our imagination in reality.

Three points I quickly want to make.

1. I just watched marksmen on the History Channel adjusting their guns for wind and GRAVITY--in 1000 yards the bullet would drop 370 inches.

2. We send up satellites and have to periodically adjust their orbit because of GRAVITATION--yet the earth has had no one adjust it's orbit in 4.5 revolutions.

3. A while back, on "The Universe," I saw that there are very large Jupiter size planets very near their stars in other systems. The explanation was that they had migrated in. The Earth has been at a life sustaining distance from the sun for at least 3.4 billion years according to the geographic timescale (appearance of first blue green algae fossils).

So how did the earth perfectly counteract the pull of gravitation? There should have been a drag on our momentum, slowing us down.

If you say the outer planets, they can't speed the earth back up after the sun's gravitation has slowed it down. Even if they did counteract the sun's gravitation, how did they happen to sync just right to keep the earth in orbit without migrating in or out themselves?

#2 numbers

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Posted 23 January 2010 - 11:47 PM

One of the most perplexing questions to me, if I bought into the modern cosmological age of the universe, is how did the earth not migrate into the sun, or fly off into space by now. Four and half billion orbits is simply past our imagination in reality.

Three points I quickly want to make.

1.  I just watched marksmen on the History Channel adjusting their guns for wind and GRAVITY--in 1000 yards the bullet would drop 370 inches.

What is the point you are trying to make here? What you are describing is the basic principle behind orbit. The bullet falls but to make it orbit simply requires that it travels fast enough that the curve of the earth causes the ground to keep distance with the falling bullet.

Newton's cannon example.
http://spaceplace.na...s/orbits1.shtml

2.  We send up satellites and have to periodically adjust their orbit because of GRAVITATION--yet the earth has had no one adjust it's orbit in 4.5 revolutions.

We have to adjust satellites because they experience drag from the upper portion of the earth's atmosphere, not because of gravitation. Just an example of the point, the moon is far enough away not to experience atmospheric drag and it doesn't require periodic correction.

http://en.wikipedia....i/Orbital_decay
Atmospheric drag exerts a significant effect at the altitudes of space stations, space shuttles and other manned Earth-orbit spacecraft, and satellites with relatively high orbits such as the Hubble Space Telescope.

3.  A while back, on "The Universe,"  I saw that there are very large Jupiter size planets very near their stars in other systems.  The explanation was that they had migrated in.  The Earth has been at a life sustaining distance from the sun for at least 3.4 billion years according to the geographic timescale (appearance of first blue green algae fossils).

So how did the earth perfectly counteract the pull of gravitation?  There should have been a drag on our momentum, slowing us down.

If you say the outer planets, they can't speed the earth back up after the sun's gravitation has slowed it down.  Even if they did counteract the sun's gravitation,  how did they happen to sync just right to keep the earth in orbit without migrating in or out themselves?

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You might find this article interesting
http://www.space.com...aas-100107.html. It appears to provide a solution to your question.

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Posted 24 January 2010 - 12:07 AM

Your question is answered by a simple classical mechanics derivation. According to the well-received theories, such as those of Newton (which even people like you ascribe to), planets travel in elliptical orbits, and that's just how it works out. Not elliptical orbits that slowly decrease in radius -- not elliptical orbits that change speed up or slow down randomly -- just elliptical orbits that remain the same elliptical orbits.

#4 ikester7579

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Posted 24 January 2010 - 01:17 AM

AFJ, don't you know it just happens?

I get your point but they refuse to see it.

#5 AFJ

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Posted 24 January 2010 - 06:37 AM

We have to adjust satellites because they experience drag from the upper portion of the earth's atmosphere, not because of gravitation.  Just an example of the point, the moon is far enough away not to experience atmospheric drag and it doesn't require periodic correction.
http://en.wikipedia....i/Orbital_decay

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Thank you numbers. I am intuitively thinking here, because my background in physics is very general. I understand that friction from the atmosphere would be a factor, but to say that gravitational pull does not cause a drag and slow things down is counter-intuitive.

So I did a little digging and found this on wikipedia: "Dynamical friction is a term in astrophysics related to loss of momentum and kinetic energy of moving bodies through a gravitational interaction with surrounding matter in space. It is sometimes referred to as gravitational drag, and was first discussed in detail by Subrahmanyan Chandrasekhar in 1943."

For our physics folks, the math is there also--under the Chandrasekhar dynamical friction formula.

AFJ said...
I just watched marksmen on the History Channel adjusting their guns for wind and GRAVITY--in 1000 yards the bullet would drop 370 inches.


numbers said...
The bullet falls but to make it orbit simply requires that it travels fast enough that the curve of the earth causes the ground to keep distance with the falling bullet.


I think I understand the idea your posing, but I would say this is incorrect. The bullet is going to fall relative to the center of the earth. The force of gravity would be a right angle down from a horizontal trajectory of the bullet, no matter how far the bullet went, how the earth curves, nor how much the bullet's angle changed relative to a third object in space.

Posted Image

The momentum of a bullet going fast enough for orbit would try to keep it in a straight line of motion relative to the sun--this is the cause of centrifugal force. It would "pull" against gravity. The angle of gravity on a sphere is always changing as the bullet travels. But the kinetic energy in a very fast bullet would try to angle the bullet in a straight line relative to a third object in space, not the ground. If these two forces stay in equilibrium the bullet will stay parallel to the ground forever (in a vacuum). However, the initial thrust of the gunpowder will not keep the bullet in flight--it has to have additional periodic thrust to maintain it's kinetic energy, and hence--momentum.

Again, intuitively, I would say in the example of orbit, we have the dynamics of centrifugal force in equilibrium with gravitational pull. Not anything to do with the curvature of anything, except possibly space (?). Nor the "falling" of anything parallel with the curvature of the Earth (or the sun).

#6 jason777

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Posted 24 January 2010 - 09:06 AM

Another factor is the fact that our sun has burned 4.5 billion years worth of gas.How much bigger was it? And how much did it affect the orbit?

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Posted 24 January 2010 - 09:31 AM

The momentum of a bullet going fast enough for orbit would try to keep it in a straight line of motion relative to the sun--this is the cause of centrifugal force.  It  would "pull" against gravity.  The angle of gravity on a sphere is always changing as the bullet travels.  But the kinetic energy in a very fast bullet would try to angle the bullet in a straight line relative to a third object in space, not the ground.  If these two forces stay in equilibrium the bullet will stay parallel to the ground forever (in a vacuum). However, the initial thrust of the gunpowder will not keep the bullet in flight--it has to have additional periodic thrust to maintain it's kinetic energy, and hence--momentum.

Again, intuitively, I would say in the example of orbit, we have the dynamics of centrifugal force in equilibrium with gravitational pull.  Not anything to do with the curvature of anything, except possibly space (?). Nor the "falling" of anything parallel with the curvature of the Earth (or the sun).

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Number is right, it has everything to do with the curvature of the earth.

Low earth satellites and spaceships are in a constant state of 'falling', the reason that they do not hit the ground, is that their velocity matches the rate at which the ground curves away from them.
Their velocity does not change due to the lack of friction in a near vacuum (low earth satellites do encounter molecules of atmosphere and their speed does degrade over time)

This is basic Newtonian physics.

Peace

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Posted 24 January 2010 - 10:02 AM

One of the most perplexing questions to me, if I bought into the modern cosmological age of the universe, is how did the earth not migrate into the sun, or fly off into space by now. Four and half billion orbits is simply past our imagination in reality.

Three points I quickly want to make.

1.  I just watched marksmen on the History Channel adjusting their guns for wind and GRAVITY--in 1000 yards the bullet would drop 370 inches.

2.  We send up satellites and have to periodically adjust their orbit because of GRAVITATION--yet the earth has had no one adjust it's orbit in 4.5 revolutions.

3.  A while back, on "The Universe,"  I saw that there are very large Jupiter size planets very near their stars in other systems.  The explanation was that they had migrated in.  The Earth has been at a life sustaining distance from the sun for at least 3.4 billion years according to the geographic timescale (appearance of first blue green algae fossils).

So how did the earth perfectly counteract the pull of gravitation?  There should have been a drag on our momentum, slowing us down.

If you say the outer planets, they can't speed the earth back up after the sun's gravitation has slowed it down.  Even if they did counteract the sun's gravitation,  how did they happen to sync just right to keep the earth in orbit without migrating in or out themselves?

View Post


The elliptical orbit takes the Earth to different distances. As it approaches the sun, the Earth begins to accelerate. It goes around the sun and is slowed down as it begins to come back toward the sun. This is actually similar to the gravitational slingshot used by Nasa when they need to alter the path of a probe.

Sattelites are pulled down by atmospheric drag, not by gravitation. The gravitational effects of the sun and moon actually do more to displace the sattelite than the earth's gravity.

#9 AFJ

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Posted 24 January 2010 - 10:59 AM

The elliptical orbit takes the Earth to different distances.  As it approaches the sun, the Earth begins to accelerate.  It goes around the sun and is slowed down as it begins to come back toward the sun.  This is actually similar to the gravitational slingshot used by Nasa when they need to alter the path of a probe. 

Sattelites are pulled down by atmospheric drag, not by gravitation.  The gravitational effects of the sun and moon actually do more to displace the sattelite than the earth's gravity.

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Aparrently, you guys are ignoring the fact that gravitation produces drag. No one made any comment to refute dynamicalal friction.

Momentum and kinetic energy are 7th grade physics. Where there is no gravitation, momentum will keep objects going in a straight line at the same velocity. The conservation of energy will transfer kinetic energy by dynamical friction:

Think..."of a massive object moving through a cloud of smaller lighter bodies. The effect of gravity causes the light bodies to accelerate and gain momentum and kinetic energy (see slingshot effect). By conservation of energy and momentum, we may conclude that the heavier body will be slowed by an amount to compensate. Since there is a loss of momentum and kinetic energy for the body under consideration, the effect is called dynamical friction." http://en.wikipedia....vitational_drag

If you want to say the object is falling in parallel with the curvature of the earth--fine. But you are going to lose kinetic energy eventually--and by that momentum and velocity. If I throw a ball as hard as I can to you and you are 10 feet away, your hand will smart because of the kenetic energy transferred into your hand. But if you are 200 feet away and I throw it to you, you will be able to catch it with no pain--the ball having lost momentum and kinetic energy. This going to happen because gravity will drag on the ball taking away kinetic energy.

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Posted 24 January 2010 - 01:28 PM

Aparrently, you guys are ignoring the fact that gravitation produces drag.  No one made any comment to refute dynamicalal friction. 

Momentum and kinetic energy are 7th grade physics.  Where there is no gravitation, momentum will keep objects going in a straight line at the same velocity.  The conservation of energy will transfer kinetic energy by dynamical friction:

Think..."of a massive object moving through a cloud of smaller lighter bodies. The effect of gravity causes the light bodies to accelerate and gain momentum and kinetic energy (see slingshot effect). By conservation of energy and momentum, we may conclude that the heavier body will be slowed by an amount to compensate. Since there is a loss of momentum and kinetic energy for the body under consideration, the effect is called dynamical friction."  http://en.wikipedia....vitational_drag

If you want to say the object is falling in parallel with the curvature of the earth--fine.  But you are going to lose kinetic energy eventually--and by that momentum and velocity.  If I throw a ball as hard as I can to you and you are 10 feet away, your hand will smart because of the kenetic energy transferred into your hand.  But if you are 200 feet away and I throw it to you, you will be able to catch it with no pain--the ball having lost momentum and kinetic energy.  This going to happen because gravity will drag on the ball taking away kinetic energy.

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A loss of energy doesn't mean falling or stopping. The loss of energy in the Earth-Sun system might effect the Sun or the Earth. This is especially important in the Earth-Sun system because you have to account for gravity and by extension the potential energy of the system.

#11 numbers

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Posted 24 January 2010 - 01:30 PM

Aparrently, you guys are ignoring the fact that gravitation produces drag.  No one made any comment to refute dynamicalal friction. 

Momentum and kinetic energy are 7th grade physics.  Where there is no gravitation, momentum will keep objects going in a straight line at the same velocity.  The conservation of energy will transfer kinetic energy by dynamical friction:

Think..."of a massive object moving through a cloud of smaller lighter bodies. The effect of gravity causes the light bodies to accelerate and gain momentum and kinetic energy (see slingshot effect). By conservation of energy and momentum, we may conclude that the heavier body will be slowed by an amount to compensate. Since there is a loss of momentum and kinetic energy for the body under consideration, the effect is called dynamical friction."  http://en.wikipedia....vitational_drag

If you read the formula you'd see that it requires traveling through a cloud of matter. Where exactly is the cloud of stuff that you think the earth has been traveling through for 4.5 billion years?

F = C * G^2 * M^2 * p^2 / v^2

G = gravitational constant (value known)
M = mass of earth (value known)
p = density of cloud (value needed)
v = velocity of earth (value known)
C = coefficient (value needed)

I am perfectly happy to show you that dynamic friction doesn't have a significant impact on the earth but I need you to provide the values that you feel are acceptable. In other words what value for p (density of the cloud that earth travels through) do you want to use, and what value for C?


If you want to say the object is falling in parallel with the curvature of the earth--fine.  But you are going to lose kinetic energy eventually--and by that momentum and velocity.  If I throw a ball as hard as I can to you and you are 10 feet away, your hand will smart because of the kenetic energy transferred into your hand.  But if you are 200 feet away and I throw it to you, you will be able to catch it with no pain--the ball having lost momentum and kinetic energy.  This going to happen because gravity will drag on the ball taking away kinetic energy.

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Sorry but this is completely and totally wrong. You should really look up what orbit is and how it works. The ball slows because you are throwing in a atmosphere. If you were in a vacuum and threw a ball to me, the ball would hit my hand just as hard as it left yours (I am ignoring tidal effects for simplicity). The dynamic friction you mention would only matter if the ball were passing through a cloud of objects.

#12 AFJ

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Posted 24 January 2010 - 04:31 PM

If you read the formula you'd see that it requires traveling through a cloud of matter. Where exactly is the cloud of stuff that you think the earth has been traveling through for 4.5 billion years?

F = C * G^2 * M^2 * p^2 / v^2

G = gravitational constant (value known)
M = mass of earth (value known)
p = density of cloud (value needed)
v = velocity of earth (value known)
C = coefficient (value needed)

I am perfectly happy to show you that dynamic friction doesn't have a significant impact on the earth but I need you to provide the values that you feel are acceptable.  In other words what value for p (density of the cloud that earth travels through) do you want to use, and what value for C?
Sorry but this is completely and totally wrong.  You should really look up what orbit is and how it works.  The ball slows because you are throwing in a atmosphere.  If you were in a vacuum and threw a ball to me, the ball would hit my hand just as hard as it left yours (I am ignoring tidal effects for simplicity).  The dynamic friction you mention would only matter if the ball were passing through a cloud of objects.

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I am not discounting theory on orbit, nor trying to be hard headed. But gravitation is gravitation. And friction is still friction no matter the cause. Put it in any model you want. You can give me all the math you want and you will still have gravity pulling at a (app) right angle to the earth. The trajectory is still horizontal compared to the surface of the sun. And the momentum of the earth still wants to go in a straight line.

SO you still have "horizontal" momentum fighting "vertical" gravitation. Relatively the forces are at a right angle to each other. If you drag on force of momentum long enough you decrease momentum--friction.

It doesn't make sense to say that the friction of air causes orbital decay, but not the friction caused by gravitation. Unless you want to deny gravitation causes friction.

Now if you want to talk about sling shot effect, for a rocket, it still takes thrust to achieve the necessary effect. You are saying that the whole thing keeps going forever--it syncs just right like some kind of eternal machine. And it all happened by unconscious laws. Sounds pretty intelligent to me, and I do not think it happens without unseen power.

#13 numbers

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Posted 24 January 2010 - 05:43 PM

I am not discounting theory on orbit, nor trying to be hard headed.  But gravitation is gravitation. And friction is still friction no matter the cause.  Put it in any model you want.  You can give me all the math you want and you will still have gravity pulling at a (app) right angle to the earth.  The trajectory is still horizontal compared to the surface of the sun.  And the momentum of the earth still wants to go in a straight line. 

SO you still have "horizontal" momentum fighting "vertical" gravitation. Relatively the forces are at a right angle to each other.  If you drag on force of momentum long enough you decrease momentum--friction.

I think I know where you are getting confused. You may need to look up vectors to understand the concepts but a force along the X axis is independant of a force along the Y axis.

The horizontal motion of a ball/planet is not affected by the vertical force of gravity, the two are independant of each other. This is a basic principle in math and physics. The length of a vector along the X axis cannot be changed by a vector along the Y axis. It can only change by the addition or subtraction of another vector along the X axis. For gravity to cause a orbiting body to slow, it would have to act along a horizontal direction, not a vertical direction.

It doesn't make sense to say that the friction of air causes orbital decay, but not the friction caused by gravitation.  Unless you want to deny gravitation causes friction.

See above, there is no orbital decay caused by gravitation because there is no X component to the gravity of a body being orbited. Only if you are moving past/through a mass where the gravity of the body is acting along the direction of your motion can gravity slow you down or speed you up.

I'd still like an answer to my question. According to the source you quoted, dynamic friction requires a massive object be moving through a cloud of lighter objects.

...a massive object moving through a cloud of smaller lighter bodies...

For this to apply to the earth over 4.5 billion years would require that the earth be moving through a cloud of lighter objects for 4.5 billion years. What and where is this cloud that you feel is responsible for the frictional effect you claim exists? Or are you dropping the dynamic friction claim?

#14 AFJ

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Posted 24 January 2010 - 09:54 PM

For this to apply to the earth over 4.5 billion years would require that the earth be moving through a cloud of lighter objects for 4.5 billion years.  What and where is this cloud that you feel is responsible for the frictional effect you claim exists?  Or are you dropping the dynamic friction claim?

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After studying a bit on sling shot effect, I find that gravity and the motion of a planet can be used to accelerate or decelerate spacecraft. It all depends on the relative approach by the smaller object, it's velocity and, it's altitude of orbit around the planet, of course.

Here is the gravity assist acceleration:

Posted Image

In this illustration the planet is moving left at velocity U--the craft is moving right at v. We are observing from a third reference point. The craft is pulled in, follows orbit at a specific orbit elevation, and then escapes because it is moving at 2U + v. It follows a hyperbole path.

Here is the gravitational deceleration:

Posted Image

This one, because of it's distance from the planet, it's approach and the motion of the planet, causes gravitational drag.

The earth being in an elliptical orbit, we need to remember that the sun is in motion also. So an elliptical would have somewhat of a slingshot effect, but apparently must have a deceleration effect also, otherwise we would become irregular,and finally escape or plunge. If the sun is in motion then it's gravitation should speed us up, then slow us down, as we move against it's motion, relative to Andromeda.

This would seem to point to an intricate system which would be hard to imagine as a random event put into motion by nothing intelligent. It would be the same as saying you knocked all the pool balls into the pockets on the break!

So, now I have a question for everyone.
1. If a space craft is moving in deep orbit with negligible atmospheric drag, at 17k mph, does that mean you're falling at 17000 mph? Why can you not look at it as pulling away in a straight line relative to the surface of the earth--it could be called relative inertia?

2. Either way the question is truly, How big is the margin of velocity/distance from surface/relative elliptical/ motion of star, to put something in an eternal orbit? It would seem that the cause of initial velocity/shape of orbit/motion of star would not be random or unconscious, especially in an elliptical. Too fast would cause escape, or an irregular orbit which would eventually cause a plunge into the sun. Too slow would cause a plunge.

3. And if there is gravitational drag which can be evidenced by illustration 2 (as well as a pendulum), how did the slingshot effect of our elliptical orbit completely offset the drag of the sun's motion, relative to Andromeda? In my reading, it seems that some of Einstein's calculations predicted a slow offset of our orbit.

Bottom line--4.5 billion revolutions shows near perfection. To attribute this to only our understanding of natural laws, which could change with the next big discovery, seems quite arrogant to me!

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Posted 24 January 2010 - 10:25 PM

After studying a bit on sling shot effect, I find that gravity and the motion of a planet can be used to accelerate or decelerate spacecraft.  It all depends on the relative approach by the smaller object, it's velocity and, it's altitude of orbit around the planet, of course.

Here is the gravity assist acceleration:

Posted Image

In this illustration the planet is moving left at velocity U--the craft is moving right at v.  We are observing from a third reference point.  The craft is pulled in, follows orbit at a specific orbit elevation, and then escapes because it is moving at 2U + v. It follows a hyperbole path.

Here is the gravitational deceleration:

Posted Image

This one, because of it's distance from the planet, it's approach and the motion of the planet, causes gravitational drag.

View Post

You might want to look at that second example again, it doesn't show gravitational drag at all. Both are examples of gravitational acceleration. Notice that in the second example the velocity after is greater than the velocity before. |V + Uafter| > |V + Ubefore|

The earth being in an elliptical orbit, we need to remember that the sun is in motion also.  So an elliptical would have somewhat of a slingshot effect, but apparently must have a deceleration effect also.  If the sun is in motion then it's gravitation should speed us up, then slow us down, as we move against it's motion.

This would seem to point to an intricate system which would be hard to imagine as a random event put into motion by nothing intelligent.  It would be the same as saying you knocked all the pool balls into the pockets on the break!  Even with all our filled chalkboards, we still "see through a glass darkly."

If the earth accelerates as we move with the sun and decelerates as we move against the sun, where exactly is the overall net deceleration coming from that you are arguing for?

I already posted an article showing how the early protoplanets could achieve stable orbits around the sun in my first reply to this topic.


P.S.
I'd still like an answer to my question. According to the source you quoted, dynamic friction requires a massive object be moving through a cloud of lighter objects.
For this to apply to the earth over 4.5 billion years would require that the earth be moving through a cloud of lighter objects for 4.5 billion years. What and where is this cloud that you feel is responsible for the frictional effect you claim exists? Or are you dropping the dynamic friction claim?

Edit: You appear to have added to your post after I wrote this response, I'll try and address your 3 questions later.

#16 Bruce V.

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Posted 25 January 2010 - 07:51 AM

Great thread.

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Posted 25 January 2010 - 01:03 PM

I am not discounting theory on orbit, nor trying to be hard headed.  But gravitation is gravitation. And friction is still friction no matter the cause.  Put it in any model you want.  You can give me all the math you want and you will still have gravity pulling at a (app) right angle to the earth.  The trajectory is still horizontal compared to the surface of the sun.  And the momentum of the earth still wants to go in a straight line. 

SO you still have "horizontal" momentum fighting "vertical" gravitation. Relatively the forces are at a right angle to each other.  If you drag on force of momentum long enough you decrease momentum--friction.

View Post


It isn't only horizontal momentum. The Earth's distance from the surface of the Sun varies hence there is a vertical component to the Earth's motion relative to the Sun. Take the ball you mentioned earlier, if you threw it in a vacuum here on Earth it would fall, but when it hit the ground it would still be moving away from you at the same speed as when you threw it.

Gravity doesn't exist just along a single axis perpendicular either. The gravitational force between the Earth and Sun is acting on all points of both bodies although it isn't equal.

1. If a space craft is moving in deep orbit with negligible atmospheric drag, at 17k mph, does that mean you're falling at 17000 mph? Why can you not look at it as pulling away in a straight line relative to the surface of the earth--it could be called relative inertia?

View Post


Are you saying the space craft is going through 17k miles of arc every hour??? Google Newton's cannon, and you'll have your answer.

3. And if there is gravitational drag which can be evidenced by illustration 2 (as well as a pendulum), how did the slingshot effect of our elliptical orbit completely offset the drag of the sun's motion, relative to Andromeda? In my reading, it seems that some of Einstein's calculations predicted a slow offset of our orbit.

View Post


As the Sun approaches Earth it speeds up. When it gets to its point closest to the Sun acceleration is 0. Then it begins to slow down. There's no drag. Any kinetic energy lost is regained as potential energy as the Earth gets farther from the Sun.

Bottom line--4.5 billion revolutions shows near perfection. To attribute this to only our understanding of natural laws, which could change with the next big discovery, seems quite arrogant to me!


I don't think you'd have a single astrophysicist would tell you the Earth's orbit around the Sun has been the same since it the Solar system was born.

#18 numbers

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Posted 25 January 2010 - 04:44 PM

So, now I have a question for everyone. 
1. If a space craft is moving in deep orbit  with negligible atmospheric drag, at 17k mph, does that mean you're falling at 17000 mph? Why can you not look at it as pulling away in a straight line relative to the surface of the earth--it could be called relative inertia?

The simplest answer is that you're falling at whatever speed a stationary object would fall at the same distance from earth. Remember, gravity doesn't care about how fast you are moving perpendicular to it's pull. X and Y vectors are independent of each other.

2.  Either way the question is truly, How big is the margin of velocity/distance from surface/relative elliptical/ motion of star, to put something in an eternal orbit?  It would seem that the cause of initial velocity/shape of orbit/motion of star would not be random or unconscious, especially in an elliptical.  Too fast would cause escape, or an irregular orbit which would eventually cause a plunge into the sun.  Too slow would cause a plunge. 


The answer depends on the gravity of the star in question and the distance from the star. The low limit is the minimum velocity required to not hit the star, the high limit is the escape velocity for the star at whatever distance you want to orbit at. Everything in between will result in orbit around the star.

[Extremely simplified explanation]
The stuff that made the earth started out as part of a rotating disc of stuff. Any stuff that was moving fast enough to escape, escaped the disc. Any stuff that was moving too slow fell into the center and became part of the sun (99.5% of the stuff in the solar system). The leftover stuff, which by process of elimination we can say wasn't moving too fast or too slow, became the planets.
[/Extremely simplified explanation]

3. And if there is gravitational drag which can be evidenced by illustration 2 (as well as a pendulum), how did the slingshot effect of our elliptical orbit completely offset the drag of the sun's motion, relative to Andromeda?  In my reading, it seems that some of Einstein's calculations predicted a slow offset of our orbit.


1. Illustration 2 is gravitational acceleration, not drag.
2. Pendulums don't experience gravitational drag.
3. Slingshot effects cannot happen from orbits, only from one-pass flybys.
4. You are probably thinking of gravitational waves with the Einstein reference, completely different topic and completely irrelevant to the issue of the earth's orbit (we aren't orbiting binary black holes)

#19 AFJ

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Posted 25 January 2010 - 08:25 PM

You might want to look at that second example again, it doesn't show gravitational drag at all.  Both are examples of gravitational acceleration.  Notice that in the second example the velocity after is greater than the velocity before. |V + Uafter| > |V + Ubefore|

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First, sorry, I read the sentence under this illustration on Wiki without studying the equation. It was talking about deceleration and I assumed this was the illustration. Hey, I'm not putting out pretenses here--I'm not a physics dude, so I appreciate your patience.

If the earth accelerates as we move with the sun and decelerates as we move against the sun, where exactly is the overall net deceleration coming from that you are arguing for?

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I am assuming that if the solar system and earth were not designed, then we can almost be positive that the orbit is not going to be perfect for eternity, or 4.5 billion years. Even the slightest offset over time without intelligent adjustment will eventually produce an unstable orbit.

We have thrusters on our spacecraft to make adjustments even after we make all our calculations, do our orbits and gravity assists. The earth does not have this yet stays in perfect orbit.

So the combination of no intelligent agent to compensate for any net deceleration or acceleration in the orbit, even though it be slight--over time it should cause instability or escape without some type of adjustment. Or any other cause such as solar winds, asteroid impacts, passing comets etc. And to believe that this orbit continues in this elliptical for at least 3.4 billion with no adjustment necessary and with no intelligent initiator, nor "lawmaker" is, in my opinion, an extremely large leap of faith in your theory.

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Posted 25 January 2010 - 09:16 PM

We have thrusters on our spacecraft to make adjustments even after we make all our calculations, do our orbits and gravity assists.  The earth does not have this yet stays in perfect orbit.

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A gravity assist isn't used to correct an orbit. An object moving away from the Sun is going against the gravitational force between the two. Gravitational assists are used to speed up a probe not to correct an orbit. I said the Earth's motion was similar to one because it speeds up as it approaches the Sun.

So the combination of no intelligent agent to compensate for any net deceleration or acceleration in the orbit, even though it be slight--over time it should cause instability or escape without some type of adjustment.  Or any other cause such as solar winds, asteroid impacts,  passing comets etc. And to believe that this orbit continues in this elliptical for at least 3.4 billion with no adjustment necessary and with no intelligent initiator, nor "lawmaker" is, in my opinion, an  extremely large leap of faith in your theory.

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Well what do you define as orbital stability??? As I said, no astrophysicist or astronomer would say the Earth's has remained the same. Predicting motion of more than two objects is really beyond our math. LaGrange's solution was to simplify the whole thing with his five points. Everything you mentioned plus surrounding stars, the center of the galaxy, and whatever else figures in.

That said, the Sun exerts the most influence on the Earth by far. Why do you think the Earth's orbit requires correction???




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