Maybe this is just me being a curmudgeon, which is likely...
I seem to have a category in my brain for cool, creative internet stuff that will last as long as it lasts, but probably won't be replaced by the modern internet.
Anyway.. these days.. xkcd would be starting on Twitter, FB or pictogram. Back then it was blogrolls and Reddit. The medium is the message and the discovery channel is the medium, I think.
Do you know of any similar websites? I have a couple of questions that I would like to see answered. I emailed mr Munroe in the past but he never replied, I'm sure he has thousands of questions from readers to choose from.
/r/AskScience on Reddit is pretty great in getting your random questions answered - perhaps not in the same entertaining way, but there's definitely some smart people there.
What material would you suggest is strong enough to handle the orbit of two massive bodies (relative to girth of a poll one could realistically hold onto)? And what do you suppose the consequences of altering the moons orbit would be?
Something with elasticity would be a better option than something that is strong but even that wouldn't resolve some of the other issues presented; such as the moons surface not being geostationary to any point on the Earth.
...not without tearing the moon apart in the process. At which point you have much bigger issues (as well as no need for a pole in the first place).
But given you're just making absurd "just do X" style statements I'm sure you'll reply with some remark about gluing the moon back together or wrapping it in clingfilm before you insert the pole to strengthen it's integrity.
"What material would you suggest is strong enough to handle the orbit of two massive bodies (relative to girth of a poll one could realistically hold onto)?"
I'm not sure that question is well-defined; to the best of our knowledge we're firmly in the realm of magic here regardless of the details. Nothing even like a metal pole could traverse that distance. The materials that just might barely work to build a space elevator from Earth to Earth geostationary orbit are strong against tension, but this "pole" would be experiencing not only a lot more of that, but also some shear forces, and given how close to the theoretical maxes the space elevator already is, I don't think I have to work any math to know that it's just out of the question.
But as mentioned, you can't attach the other end to Earth because Earth rotates much faster than the moon orbits. So the strength or elasticity of the pole isn't relevant here (but obviously it's relevant in the context of getting it to not buckle/snap under its own weight!)
At these scales the rock that makes up the Earth and Moon is just a low-viscosity liquid. A strong pole would just go through the Earth without a ripple.
I would imagine that what the five year old who asked wanted was an intuitive sense of how far away the moon is. My answer would have been far less interesting. I would assume a reasonable rate at which a child slides down a pole, say 1 meter per second, multiplied by roughly 384,000km from the moon to Earth, and it would take a little over 12 years.
Let me guess - your favorite map projection is Goode Homolosine. You like easy solutions. You think we wouldn't have so many problems if we'd just elect normal people to Congress instead of Politicians. You think airlines should just buy food from the restaurants near the gates and serve that on board. You change your car's oil, but secretly wonder if you really need to.
You never know with 5 years old. It could be what you say, or it could be some topic they are deeply interested in and will want to know all the little tiny details.
I had a discussion with some 4 years old about fire extinguisher and why there were 2 at the nursery. My simple explanation was disappointing to one and I learned from his mom that it ended up looking the various type of firetruck and what number of what type of fire extinguisher they were carrying as well as the various hose option, the different type of fire and the various safety labels on product helping determining the type of fire they produce, ...
The others where also unhappy with the few details I provided, it seems "there is a big one and a smaller one" was what they were expecting.
Perhaps this could has been in the first paragraph, as an easy comparison (1m/s looks too small). And then add the details of the variation of the Earth gravity with the distance and then the part about the gravity of the Moon, and then in the third paragraph get to the complete technical explanation.
Anyway, sending a question to "What If?" is like sending a question to Mythbusters. You never get an easy answer, but an overthinked answer that involves some destruction and explosions.
The (fire) pole wouldn't meet the (geographic) pole vertically. In fact, I suspect it would have to travel through the Earth, which might be a little bit disruptive as the moon orbits...
You're going to have yet more fun with the fact that as your position on the (metal) pole approaches the (planetary) pole, gravity is going to start tilting until at the very end you are traveling horizontally, or at least close to it.
Evaluating how much this effects the problem is difficult, as for the (metal) pole meeting Earth on the equator the answer is "laughably impossible", and for the (metal) pole meeting at (Earth's) pole the answer is "laughably impossible", and which one is "harder" will depend entirely on your assumptions about how the impossibilities relate. Relative to having actually climbed up to L1 and relative to surviving descent into Earth, being on a horizontal pole rather than a vertical one may not be seen as a very big deal.
It must be so fun to have a Dad that entertains your foolish ideas as a child, and play them out in immense detail for you :) I hope I can be that Dad one day.
The question asker’s father (Ramon Schönborn) is not the same person as the answerer (Randall Munroe). But nonetheless it would be fun to have a dad who sends your questions to random internet cartoonists to entertain your foolish ideas for them, too.
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.
> 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.
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.
> 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.
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...
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.
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.
> 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 ... ?"
Hey Randall!
If you put a microwave in a sub-zero walk-in fridge, and after the device had reached equilibrium with ambient conditions, you connected the microwave to mains power, then put a chunk of ice in the microwave and turned it on at full power, would the ice ever melt?
but what if microwaves don't heat solid ice at all, they heat the water that forms on the ice because the microwave is at room temperature? google "how to melt glass in a microwave".
The "mathing it out" takes about as long as he has before he needs to actually start writing and putting the post together. The problems can involve a lot of research since there's basically no end to how far you can take a given question. The whole thing usually takes less than a week of on and off work.
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[ 3.4 ms ] story [ 135 ms ] threadI seem to have a category in my brain for cool, creative internet stuff that will last as long as it lasts, but probably won't be replaced by the modern internet.
Anyway.. these days.. xkcd would be starting on Twitter, FB or pictogram. Back then it was blogrolls and Reddit. The medium is the message and the discovery channel is the medium, I think.
Then use a pole that is strong enough to eliminate this problem.
Probably bad ones.
Something with elasticity would be a better option than something that is strong but even that wouldn't resolve some of the other issues presented; such as the moons surface not being geostationary to any point on the Earth.
The pole would also solve that problem ...
But given you're just making absurd "just do X" style statements I'm sure you'll reply with some remark about gluing the moon back together or wrapping it in clingfilm before you insert the pole to strengthen it's integrity.
The solution is obviously attaching rockets to the moon to accelerate it first.
I'm not sure that question is well-defined; to the best of our knowledge we're firmly in the realm of magic here regardless of the details. Nothing even like a metal pole could traverse that distance. The materials that just might barely work to build a space elevator from Earth to Earth geostationary orbit are strong against tension, but this "pole" would be experiencing not only a lot more of that, but also some shear forces, and given how close to the theoretical maxes the space elevator already is, I don't think I have to work any math to know that it's just out of the question.
I had a discussion with some 4 years old about fire extinguisher and why there were 2 at the nursery. My simple explanation was disappointing to one and I learned from his mom that it ended up looking the various type of firetruck and what number of what type of fire extinguisher they were carrying as well as the various hose option, the different type of fire and the various safety labels on product helping determining the type of fire they produce, ...
The others where also unhappy with the few details I provided, it seems "there is a big one and a smaller one" was what they were expecting.
(Sorry for saying the (possibly) obvious.)
And this is what makes it wonderful.
Anyway, sending a question to "What If?" is like sending a question to Mythbusters. You never get an easy answer, but an overthinked answer that involves some destruction and explosions.
Earth moon firepole staple
It would also have the advantage of providing a fixed place on the earth to find a stash of warm clothes and an energy drink.
Evaluating how much this effects the problem is difficult, as for the (metal) pole meeting Earth on the equator the answer is "laughably impossible", and for the (metal) pole meeting at (Earth's) pole the answer is "laughably impossible", and which one is "harder" will depend entirely on your assumptions about how the impossibilities relate. Relative to having actually climbed up to L1 and relative to surviving descent into Earth, being on a horizontal pole rather than a vertical one may not be seen as a very big deal.
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.
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.
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.
> 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.
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...
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.
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 ... ?"
[1] https://what-if.xkcd.com/155/
For the numbers I used a safety factor of 1. The slightest nick or scratch would cause a break. Safety factor of 3 is more sensible.