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Unfortunately it is inaccurate. Actually, the person sliding the pole would be like an object changing orbit. Remember, Moon orbits Earth. Even at L1 you can't

Unfortunately it is inaccurate. Actually, the person sliding the pole would be like an object changing orbit. Remember, Moon orbits Earth. Even at L1 you can't just push yourself and coast along the pole. The movement along the pole is changing orbits and as we know this requires energy. In this case if you push yourself along the pole you would suddenly find yourself drifting away from it. That's of course if you could create a rigid pole. As every piece of the pole would be on a different orbit there would be huge forces acting on the pole.

ColinWright 8y ago
> Actually, the person sliding the pole would be like an object changing orbit. Remember, Moon orbits Earth. Even at L1 you can't just push yourself and coast along the pole. The movement along the pole is changing orbits and as we know this requires energy. In this case if you push yourself along the pole you would suddenly find yourself drifting away from it. Suppose you tether yourself to the pole with a ring, and are closer to the Earth than L1. You now are not moving fast enough to stay in the orbit implied by your current altitude, so you move in an orbit that brings you closer to the Earth. You also try to move away from the pole, but you are tethered to it, so there is a force holding you by the pole. That force provides energy to you. So it seems to me that it does work, and I don't understand your reasoning.
- lmilcin 8y ago
  The mentioned loop around the pole attached to your waist would do but since none of the extremely detailed drawings contained the loop we must assume that the person travaled the pole without the loop. Moon orbits Earth at about 1km/s and you have to loose orbital speed as you move along the pole. Since the pole distance is about 400000km and the orbital speed to loose is 1km/s it means you need to loose about 2.5mm/s for every km of the pole that you travel. It may not sound much, but if you propel yourself along the pole in the direction of Earth at L1 you would be surprised to find yourself travelling away from the pole at 2.5mm/s after 1km. If you push yourself hard at say 36km/h (or 10m/s) and decide to get some sleep then you would travel almost 290km but you would also find yourself moving away from the pole at almost 1m/s and at about 10km from the pole.
  - ColinWright 8y ago
    Quoting: > Note: While you're flinging yourself along, be careful not to drift out of reach of the pole. Hopefully you brought some kind of safety line so you can recover if that happens. Of course you have lateral forces on the pole, that's not in question. But if you're sliding down the pole then you're, you know, sliding down the pole. That means you are hanging on to it somehow, or tethered to it, or something. The point is that if you are actually sliding down the pole then it really does actually work. > ... you would be surprised to find yourself travelling away from the pole at 2.5mm/s after 1km. No, I wouldn't be surprised at all, because I do know a little about orbital mechanics. Possibly not as much as you do, but I do give talks on it, so if you can explain clearly how sliding down a pole (once closer than L1) won't work, I'd be really interested to hear it, because so far what you're saying hasn't convinced me. If all you're doing is saying "If you're not tethered to the pole then you'll drift away from it and it won't work." then we have no problem. But I'm considering the case where we are, in fact, sliding down the pole.
    - lmilcin 8y ago
      Colin, you are right. Of course if you are sliding along it you have some option to grip it and thus provide additional force needed to keep you in the vicinity of it. Of course, if you decide to actually fall to Earth from L1 that starts becoming problem. I'm too lazy to calculate exact terminal velocity you would reach when falling L1 to Earth (it won't be the 11km/s you would reach if you were falling from Moon orbit because you also have Moon tugging you). I estimate it not lower than 9km/s (Moon has 2.4km/s escape velocity). Now, if you moved along the pole at 9km/s you would feel much more tug (noticable 2.5cm/s2) or about 1/40th of Earth surface gravity. If you were 80kg person that would mean about 2kg apparent force. Of course, by that time you wouldn't be thinking much about it as you would have other problems in mind...
      - HopDavid 8y ago
        Altitude of EML1 is about 320,000 kilometers. An ordinary 320,000 x 300 km earth orbit would be moving 10.81 km/s at perigee. As an object falls towards earth it will surge ahead of the moon and the moon will be pulling it backwards. This makes effective apogee more in the range of 300,000 km. A 300,000 x 300 km orbit has velocity of about 10.8 km/s at perigee. In other words, dropping from the neighborhood of L1 will still give you speed very close to escape velocity by the time it reaches earth. In the case of orbital tether, an elevator car would have gripping wheels in contact with the tether. If its's descending the wheels can power a generator to charge the elevator car's battery.
- HopDavid 8y ago
  A.K.A. Coriolis force. Something that needs to be looked at in space elevators and orbital tetehrs as ascending (or descending) payloads exert a sideways push (or pull) on the tether and thus induce oscillations.
m0nty 8y ago
> That's of course if you could create a rigid pole He already said it's a magical pole, I think that covers it. That also implies that some of the forces involved can be ignored for didactic purposes. I mean, the big problem with all of this is it's utterly impossible, but that's not the main point. "What if ... ?"

ColinWright 8y ago

> Actually, the person sliding the pole would be like an object changing orbit. Remember, Moon orbits Earth. Even at L1 you can't just push yourself and coast along the pole. The movement along the pole is changing orbits and as we know this requires energy. In this case if you push yourself along the pole you would suddenly find yourself drifting away from it. Suppose you tether yourself to the pole with a ring, and are closer to the Earth than L1. You now are not moving fast enough to stay in the orbit implied by your current altitude, so you move in an orbit that brings you closer to the Earth. You also try to move away from the pole, but you are tethered to it, so there is a force holding you by the pole. That force provides energy to you. So it seems to me that it does work, and I don't understand your reasoning.

lmilcin 8y ago
The mentioned loop around the pole attached to your waist would do but since none of the extremely detailed drawings contained the loop we must assume that the person travaled the pole without the loop. Moon orbits Earth at about 1km/s and you have to loose orbital speed as you move along the pole. Since the pole distance is about 400000km and the orbital speed to loose is 1km/s it means you need to loose about 2.5mm/s for every km of the pole that you travel. It may not sound much, but if you propel yourself along the pole in the direction of Earth at L1 you would be surprised to find yourself travelling away from the pole at 2.5mm/s after 1km. If you push yourself hard at say 36km/h (or 10m/s) and decide to get some sleep then you would travel almost 290km but you would also find yourself moving away from the pole at almost 1m/s and at about 10km from the pole.
- ColinWright 8y ago
  Quoting: > Note: While you're flinging yourself along, be careful not to drift out of reach of the pole. Hopefully you brought some kind of safety line so you can recover if that happens. Of course you have lateral forces on the pole, that's not in question. But if you're sliding down the pole then you're, you know, sliding down the pole. That means you are hanging on to it somehow, or tethered to it, or something. The point is that if you are actually sliding down the pole then it really does actually work. > ... you would be surprised to find yourself travelling away from the pole at 2.5mm/s after 1km. No, I wouldn't be surprised at all, because I do know a little about orbital mechanics. Possibly not as much as you do, but I do give talks on it, so if you can explain clearly how sliding down a pole (once closer than L1) won't work, I'd be really interested to hear it, because so far what you're saying hasn't convinced me. If all you're doing is saying "If you're not tethered to the pole then you'll drift away from it and it won't work." then we have no problem. But I'm considering the case where we are, in fact, sliding down the pole.
  - lmilcin 8y ago
    Colin, you are right. Of course if you are sliding along it you have some option to grip it and thus provide additional force needed to keep you in the vicinity of it. Of course, if you decide to actually fall to Earth from L1 that starts becoming problem. I'm too lazy to calculate exact terminal velocity you would reach when falling L1 to Earth (it won't be the 11km/s you would reach if you were falling from Moon orbit because you also have Moon tugging you). I estimate it not lower than 9km/s (Moon has 2.4km/s escape velocity). Now, if you moved along the pole at 9km/s you would feel much more tug (noticable 2.5cm/s2) or about 1/40th of Earth surface gravity. If you were 80kg person that would mean about 2kg apparent force. Of course, by that time you wouldn't be thinking much about it as you would have other problems in mind...
    - HopDavid 8y ago
      Altitude of EML1 is about 320,000 kilometers. An ordinary 320,000 x 300 km earth orbit would be moving 10.81 km/s at perigee. As an object falls towards earth it will surge ahead of the moon and the moon will be pulling it backwards. This makes effective apogee more in the range of 300,000 km. A 300,000 x 300 km orbit has velocity of about 10.8 km/s at perigee. In other words, dropping from the neighborhood of L1 will still give you speed very close to escape velocity by the time it reaches earth. In the case of orbital tether, an elevator car would have gripping wheels in contact with the tether. If its's descending the wheels can power a generator to charge the elevator car's battery.
HopDavid 8y ago
A.K.A. Coriolis force. Something that needs to be looked at in space elevators and orbital tetehrs as ascending (or descending) payloads exert a sideways push (or pull) on the tether and thus induce oscillations.

m0nty 8y ago

> That's of course if you could create a rigid pole He already said it's a magical pole, I think that covers it. That also implies that some of the forces involved can be ignored for didactic purposes. I mean, the big problem with all of this is it's utterly impossible, but that's not the main point. "What if ... ?"