It can't be held out by the pull of the weight on the end of it (I assume you mean the space end) unless it is sitting in the ground, supported, and the space end is out of geostationay orbit but moving fast enough to be geostationary. And that would put unneccessary strain on the cable when you can simply leave it in geostationary orbit.

Jp wrote:

To prove my point, try spinning something on a piece of string round in a circle. A heavy object, so you get the strain, etc. Now let go of it. Where does it go? It goes off in a straight line from the point at which you let go, which is not as would be predicted if centrifugal force existed. Find a physics textbook or something, they tend to run through this.

I don't need to, as I already know all this. However, I did not think I had to extend my post to twice the length by adding in common knowledge.

The fact remains. Reguardless of whether it is the way it will be done or not, the model of space elevator I speak of would stay up because of centrifugal force, not centripetal force. And it can stay in a geostationary "orbit" without actually being in a geostationary orbit because the cable keeps its orbit where we want it.

The reason that water stays in a rotating bucket is because it is moving in a straight line, and the bucket is not because it is constrained by the rope. So the water hits the walls because the walls aren't moving along the same path. That keeps the water in, not a 'centrifugal force'

Centrifugal force plays a large role. Of course it's not just a mysterious centrifugal force that makes it magically stay where it is put. Likewise, it is not merely centripetal force that keeps a satellite in orbit. They both take an outward force as well as an inward force.

The atmosphere goes around with nearly the same velocity as Earth. Otherwise, we would have blisteringly fast winds at some point on Earth, either up in the air or not. And we don't have winds fast enough that they tear apart rockets and things. Why? 'Cause we got some rockets into space. Many rockets, in fact. So atmospheric drag would be minimal. And you've failed to notice that your solution suffers from drag too, and it is the same amount of drag. Basically, it would need to keep being boosted.

The atmosphere does not stay perfectly in sync with the Earth. There is no "otherwise such and such." Find a weather textbook or something, they tend to run through this. Unless my textbook is out of date or was written by some wierd crackpot that didn't know what he was talking about, the atmosphere does not keep up.

Your solution suffers downwwards pull too. Just because the top is higher doesn't mean that it suddenly become immune.

Basically, you are increasing cable tension for no particular reason, and that isn't a good thing.

And I will add "Jp wrote: Your system suffers from the atmospheric drag too, and yours would be just as likely to come crashing down." or something to that effect. That was the main statement I wanted to reply to, but it seems you edited it before I replied.

You are correct in the first half of both the original and edited statements, but not the second halves.

Centrifugal force keeps it up despite the resistance, that is the entire point. With an outward force, you do not need the rockets as the force is already there. Therefor, it is not, as you say "for no particular reason." The Earth spins a giant bucket, satellite, whatever on the end of a cable whether it be string or nanocarbons, I don't care, the outward force is great enough to overcome the resistence. Using rockets would be the "for no particular reason" part, as centrifugal force would result when placing it farther out than geosynchronous orbit, and that would keep it up. I'm assuming that's the major factor in why most models of space elevators are above that altitude, as it makes perfect sense.

The force is there, it keeps an outward force to counteract all downward forces built up. This force is free, but rockets have an upkeep cost.

THERE IS NO CENTRIFUGAL FORCE. ANY SOLUTION INVOLVING IT WILL NOT WORK.

Your idea of sticking it further out, embedding the cable into the ground and then making it go faster, adds extra strain on the cable, but it doesn't do anything else. THINK ABOUT IT. This would be so much easier with a board I could scribble on or something...

Basically, the downwards pull applies to yours as well, because in your case, there isn't any extra force pushing outwards. It's further out, but is travelling fast enough to be geostationary, it doesn't need 'extra' force to stay out, because it will escape or go into an elliptical orbit without the cable there. What it needs is extra centripetal force. Strain on the cable provides this. So we have now added extra strain on the cable, for what? Well, once it starts being pulled down, it will begin to go into an elliptical, non-geostationary orbit. It would be better to just stick it in 'normal' geostationary orbit, because you still have the problems with falling down, etc. etc., but this way you don't have to add extra strain. The cable has enough pull on it already.

The atmosphere doesn't stay perfectly in sync, yes, but it's pretty damn close. Consider a situation where the atmosphere is a lot out. The Earth is rotating faster then the atmosphere, and the excess rotation is wind, blowing in the opposite direction to Earth's rotation. If the atmosphere is going much slower then Earth, that extra wind is huge. And I haven't noticed any extra-huge winds recently, and wind doesn't blow in the opposite direction from Earth's rotation, so the atmosphere is damn close to synchrony. The effect is minimal, given that only a very small proportion of the cable is in the atmosphere and there isn't much drag (Actually, some of it would be countered by wind blowing in the other direction).

Now, I'm going to repeat this, because it obviously hasn't sunk in. There is no centrifugal force. The water in the bucket moves in a straight line, with constant velocity, which means no force. It's just that the bucket is moving. That bucket wants to move in a straight line, but because there is a centripetal force on it (you pulling the string), it doesn't. There is no force, there is you pulling it out of that straight line path. Put a long piece of string on a toy car, and stand to the side as it moves in a straight line along a track, very quickly. Pull the string, and the car goes through a circle, and appears to pull outward. Why? Because it was travelling in a straight line and you pulled on it. It keeps trying to go in a straight line, but there is no force. THERE IS NO OUTWARD FORCE ACTING ON YOUR VERSION OF THE SATTELITE.

Any distance the spaceward end sits from geostationary orbit can be explained in that you need to put the centre of gravity in the middle of the geostationary band. The space end will sit slightly beyond that to account for the extra mass sitting underneath it, but because most of the mass is centred at the top, the centre of gravity is only a short bit down from the space end. So there is an explanation for short distances above geostationary, but not the amount you describe.

Jp wrote:

Your idea of sticking it further out, embedding the cable into the ground and then making it go faster, adds extra strain on the cable, but it doesn't do anything else. THINK ABOUT IT. This would be so much easier with a board I could scribble on or something...

Basically, the downwards pull applies to yours as well, because in your case, there isn't any extra force pushing outwards.

Now, looking at those two quotes, please answer this. If there is no extra force pushing outwards, where does this extra strain on the cable come from? It does not simply magically appear without an outward pulling force.

Strain on the cable is caused by a pull.

What it needs is extra centripetal force. Strain on the cable provides this. So we have now added extra strain on the cable, for what? Well, once it starts being pulled down, it will begin to go into an elliptical, non-geostationary orbit. It would be better to just stick it in 'normal' geostationary orbit, because you still have the problems with falling down, etc. etc., but this way you don't have to add extra strain. The cable has enough pull on it already.

It now seems like you are saying that you do need strain on the cable, but where will yours come from? If you have no outward pull, the only strain it will recieve is downward from the elevator, which won't help you at all.

The atmosphere doesn't stay perfectly in sync, yes, but it's pretty damn close. The effect is minimal, given that only a very small proportion of the cable is in the atmosphere and there isn't much drag (Actually, some of it would be countered by wind blowing in the other direction).

First off, winds coming along later and blowing in the opposite direction wouldn't eliminate the effects of the winds previously going through. Might reduce it a bit if the cable has some slack and wobbles about but not far enough to pull with the full force of the wind, but that's about all.

The effect is minimal, but not insignificant. If you have no counteracting force, even a minimal force will decay the orbit of the satellite. It seems silly to have to carry up rocket propellent every month to stabilize the orbit.

Now, I'm going to repeat this, because it obviously hasn't sunk in. There is no centrifugal force. The water in the bucket moves in a straight line, with constant velocity, which means no force. It's just that the bucket is moving. That bucket wants to move in a straight line, but because there is a centripetal force on it (you pulling the string), it doesn't. There is no force, there is you pulling it out of that straight line path. Put a long piece of string on a toy car, and stand to the side as it moves in a straight line along a track, very quickly. Pull the string, and the car goes through a circle, and appears to pull outward. Why? Because it was travelling in a straight line and you pulled on it. It keeps trying to go in a straight line, but there is no force. THERE IS NO OUTWARD FORCE ACTING ON YOUR VERSION OF THE SATTELITE.

The water most certainly is not moving in a straight line. It wants to, but outside forces are acting upon it, accelerating it inward, just like gravity does to normally orbiting satellites.

The centrifugal force is a direct result of the centripetal force in your example. The whole for every action there is a reaction bit. The force exerted by the object is directly related to the acceleration.

There most certainly is a force just as assuredly as there is me pulling it out of that straight path. My inward force pulling it out of its path exerts an equal but opposite force upon me in which it attempts to pull my out of my path. This principle is fact, and you can see it put to practical use in observatories where extrasolar planets are searched for by the "wobble effect" as they call it. As a planet's path is accelerated inward towards its star, so too does that planet exert a force on the star as well, accelerating that star in the opposite direction with an equal amount of force, though with less total acceleration since the star is more massive and moves much less.

Now, about your toy car example. You said it yourself, the car pulls on you. An outward pull. Forget all the technical definitions and whatnot, you just said yourself there is a pull there. If there is an outward pull, how can it not resist a lesser inward pull?

Let me now turn your example around. Let us say you have a toy man trying to climb away from you on the string to the toy car. That man pulls the car toward you, thus, if he is pulling hard enough, he will actually pull the car out of its path. However, if the car is allowed to extend the string so that it is farther away and yet circling with the same orbital time, it produces more strain on the string. If the toy man was pulling the car in before, he is now pulling it in less so, if at all. The car is now more resistant to work which pulls it toward you.

The bottom line is that you cannot have the thing straining the cable if it is not pulling out on the cable. It is pulling out because of its inward acceleration which keeps it in line... there's that wierd law of equal opposite reactions again. The pull is causing the strain. The pull that causes the strain can counteract a downward pull with up to the same amount of downward force as it is exerting as upward force. The very statement you keep saying, that it wants to go in a straight line, is the very statement that produces the force I speak of. If it did not want to go in a straight line, there would be no pull. It causes the pull, and it will counteract downward forces.

If you wish to discuss it any further, I suggest we take it to chatters, as now it has come down to a repetitive argument. If you truely need a demonstration, I will try to figure out how to work this new digital camera and make a short clip of myself demonstrating the principles and how the outward pull caused by the acceleration that pulls the object out of its path will counteract an inward pull.

word.

Loduwijk wrote:

Gazoot wrote:

Ridiculous! Why not put the doctrines aside, spend some hundred billion $$ on finding out how gravity works, and then we don't have to worry about fuel or extreme energy consumptions for space launches anymore.

Because, with the space elevator, we can do just that at a tenth of the cost you mention and in a tenth the time it takes to master gravity. :)

Oh, but that is thinking shortly. With gravity, launching spacecrafts will be just one of thousands of applications. Those extra dollars spent will be won back within months just in car fuel savings, probably. The whole planet can benefit from gravity devices. With a space elevator, only NASA and some rich space tourists will.

(And of course, my money assumption was a pure invention. Hopefully it can be solved with much less funding.)

Next stop after the space elevator, they better pour the money into making lots of massive antimatter factories so we can easily travel throughout our star system, and possibly even to the nearest star neighbors.

At least interplanetary travel can be done through gravity as well: Just point the device towards the sun. Wheee!!


/Gazoot

ThreeFingerPete wrote:

Jp wrote:

and wind doesn't blow in the opposite direction from Earth's rotation,

In truth, the friction of the earth against the air drags the air along with it. So wind blows WITH the rotation, exactly opposite to what you have claimed.

Not quite. He says it does not blow in the opposite direction and you say it does blow in the same direction. You're saying the same thing he did.

What you have here is a "Let's flip for it. Heads, I win. Tails, you lose."