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North Pole and Earth rotation question.

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North Pole and Earth rotation question.

Old 04-12-07, 12:35 PM
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North Pole and Earth rotation question.

I was watching Future Weapons on Discover last night and they had some fancy sniper rifle on there that would compensate for the curvature of the Earth. They also said that it would compensate for your target moving with the Earth if you were standing on the equator. Uh? Why would your target be moving faster than you are if you are on the equator?

Ok now the question regarding the thread title. If you were to stand on the North Pole or where ever the Earths axis is and you had a friend standing a few hundred feet away could you see him move around with the rotation of the Earth? That might be worth the snow dog expedition to see.
Old 04-12-07, 12:44 PM
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Take a balloon and make an equator around it. Anything north or south goes around in a tighter circle, and would be relatively faster to the equator. At least, that is the way I read it.

But that should be slower, shouldn't it?
Old 04-12-07, 12:51 PM
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Originally Posted by Mopower
Ok now the question regarding the thread title. If you were to stand on the North Pole or where ever the Earths axis is and you had a friend standing a few hundred feet away could you see him move around with the rotation of the Earth? That might be worth the snow dog expedition to see.
If I'm understanding the question correctly, then then answer is No.

Imagine you don't have a friend standing a few hundred feet away, but instead you draw a line in the snow from the point you're standing to the point your friend would be standing if he hadn't flaked out and stayed home. Now you stand at your end of that line and stare down the length of it. Would you expect to see that line rotate away from your gaze?
Old 04-12-07, 01:08 PM
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Originally Posted by jdodd
If I'm understanding the question correctly, then then answer is No.

Imagine you don't have a friend standing a few hundred feet away, but instead you draw a line in the snow from the point you're standing to the point your friend would be standing if he hadn't flaked out and stayed home. Now you stand at your end of that line and stare down the length of it. Would you expect to see that line rotate away from your gaze?

No but what if you were in a helicopter above the axis? So you wouldn't be attached to the ground in anyway.
Old 04-12-07, 01:34 PM
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A helicopter would not affect the outcome at all. We just had a discussion similar this at work. The atmosphere moves with the earth as it rotates. The helicopter is simply riding on the atmosphere. Other wise, since the earth spins at something like 1000 mph, you could travel 1000 miles around the earth just by hovering in a helicopter.
Old 04-12-07, 03:30 PM
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If this helps as an alternate idea to the helicopter/lines in snow/friend standing around thing... When I was in Alaska (not the North Pole, but more north than I usually am), you could almost perceptibly watch the stars move if you stood still for a bit. Obviously you can do that anywhere, but because we were closer to the axis point they move faster.
Old 04-12-07, 04:31 PM
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Originally Posted by Palaver
A helicopter would not affect the outcome at all. We just had a discussion similar this at work. The atmosphere moves with the earth as it rotates. The helicopter is simply riding on the atmosphere. Other wise, since the earth spins at something like 1000 mph, you could travel 1000 miles around the earth just by hovering in a helicopter.
I don't think it's the atmosphere. That would be gravity wouldn' it? If you are sitting still gravity is always pushing you down to the same point on Earth.

But if you had no gravity but your spacial orientation was steading and non moving above the axis. You would see your friend move around you wouldn't you?
Old 04-12-07, 04:57 PM
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I'm going to stick with the atmosphere being the biggest factor. Let's just say that a helicopter floats in the air, much like a person would float in water. If you were floating in a tank of water and someone spun it around, you would spin with it. The helicopter would spin/rotate with the atmosphere in much the same way.
Old 04-12-07, 05:16 PM
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Originally Posted by Palaver
I'm going to stick with the atmosphere being the biggest factor. Let's just say that a helicopter floats in the air, much like a person would float in water. If you were floating in a tank of water and someone spun it around, you would spin with it. The helicopter would spin/rotate with the atmosphere in much the same way.
On a local level the atmosphere moves in all sorts of directions - "any way the wind blows". I imagine it gets pretty windy up there at the N pole on occasions. It would be more like floating in a river than in a swimming pool.

The helicopter pilot, in order to hover over a fixed point on the ground, has to compensate for the wind strength and direction, just like you would need to swim upstream in a river to stay level with a fixed point on the bank.

If he was hovering over the N pole the earth would rotate underneath him, unless he also compensated for this rotation by rotating the helicopter. As it takes 24 hours to complete a revolution you probably wouldn't notice the movement unless you were up there for quite a while, and fixed your direction as stationary with respect to some object which wasn't rotating with the Earth - like a star. If you kept the helicopter pointing at a star then the Earth would rotate beneath you - albeit slowly.
Old 04-12-07, 05:28 PM
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But winds aren't caused by the spin of the earth on its axis.

The earth is not going to rotate underneath him. Otherwise you could hover at the equator and travel at the speed of the earth's rotation (roughly 1000 mph.) You are riding on the atmosphere which (aside from normal winds caused by pressure systems) spinds with the earth. If the earth had no atmosphere, a helicopter would not work.
Old 04-12-07, 05:52 PM
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Originally Posted by Palaver
But winds aren't caused by the spin of the earth on its axis.

The earth is not going to rotate underneath him. Otherwise you could hover at the equator and travel at the speed of the earth's rotation (roughly 1000 mph.) You are riding on the atmosphere which (aside from normal winds caused by pressure systems) spinds with the earth. If the earth had no atmosphere, a helicopter would not work.

I'm not talking about an actual helicoptor ok? I mean if you are stationary above the Earth. I just used helicopter as a reason for this. You could replace helicopter with Superman if you want or anything else that would hover without being affected by wind, gravity etc.
Old 04-12-07, 05:56 PM
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Originally Posted by Palaver
But winds aren't caused by the spin of the earth on its axis.

The earth is not going to rotate underneath him. Otherwise you could hover at the equator and travel at the speed of the earth's rotation (roughly 1000 mph.) You are riding on the atmosphere which (aside from normal winds caused by pressure systems) spinds with the earth. If the earth had no atmosphere, a helicopter would not work.
No, you are correct, winds aren't caused by the spin of the Earth, and the atmosphere does, on average, move with the rotation of the earth - which is why you don't get the 1000mph effect at the equator.

But at the pole the rotation of the atmosphere on the scale of a helicopter is going to be at a speed of, maybe pi x the length of the helicopter per 24 hours. Maybe 150 feet per 24 hours (less than 2 thousandths of a foot per second).

This very small rotation speed of the atmosphere will be completely swamped by the local variations in that average, caused by the local "wind".

So in practice he wouldn't rotate with the rotating atmosphere at the pole - unless the local wind was virtually nil, and he could otherwise hover without any other effects which might swamp the small rotating atmosphere effect - like small engine power fluctuations. At the equator the rotation speed of the atmosphere swamps the local wind speed, so you mostly float along with that rotating atmosphere, making small adjustments for the local wind to keep you stationary above a fixed point.......I think.

It's a case of the rotating atmosphere being a big effect at the equator, and a tiny effect at the poles. Actually AT the pole the rotating effect is of course 0 ft per second.
Old 04-12-07, 06:07 PM
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Originally Posted by Mopower
I'm not talking about an actual helicoptor ok? I mean if you are stationary above the Earth. I just used helicopter as a reason for this. You could replace helicopter with Superman if you want or anything else that would hover without being affected by wind, gravity etc.
Oh, well if it's Superman, that's different.

You have to ask what you mean by "stationary". It's a relative term. Stationary with respect to what? If you mean stationary with respect to the Earth, then you are rotating with it, and your friend stays put. If you mean stationary wrt the Sun, then your friend would dissappear from view quite quickly as the Earth would not only rotate him away, but it would move away from you in its orbit of the Sun as well. There is no such place as "stationary" without reference to some "frame". As Einstein might have said - "It's all relative"
Old 04-12-07, 06:10 PM
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Originally Posted by imperator505
Oh, well if it's Superman, that's different.

You have to ask what you mean by "stationary". It's a relative term. Stationary with respect to what? If you mean stationary with respect to the Earth, then you are rotating with it, and your friend stays put. If you mean stationary wrt the Sun, then your friend would dissappear from view quite quickly as the Earth would not only rotate him away, but it would move away from you in its orbit of the Sun as well. There is no such place as "stationary" without reference to some "frame". As Einstein might have said - "It's all relative"
Well if the Earth was a globe I'm talking about where the pin is in the north pole that holds the globe on it's stand. I didn't think it would that hard of a question to understand what I mean.
Old 04-12-07, 06:21 PM
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Originally Posted by Mopower
Well if the Earth was a globe I'm talking about where the pin is in the north pole that holds the globe on it's stand. I didn't think it would that hard of a question to understand what I mean.
Well, first you were standing on the N pole, then you were in a helicopter, and now you are Superman, unaffected by wind/gravity/etc. That makes 3 questions by my count - and they all have different answers.

What was the question again?
Old 04-12-07, 07:01 PM
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Originally Posted by imperator505
Well, first you were standing on the N pole, then you were in a helicopter, and now you are Superman, unaffected by wind/gravity/etc. That makes 3 questions by my count - and they all have different answers.

What was the question again?
Forget it.
Old 04-12-07, 07:25 PM
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I must have this backwards in my mind, because it seems like if the people near the pole are going around a small distance once in a day, and the people at the equator are going a much larger distance in a day, it's the people at the equator who would be moving faster.
Old 04-12-07, 08:30 PM
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*sigh* The coriolis effect only affects things that are moving on a trajectory over the surface of the Earth. Not things that are sitting on it.
Old 04-12-07, 08:40 PM
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Fool. The Earth is flat. The North Pole is where Santa lives, and we all know that Santa is fictional. Therefore, the North Pole is fictional, along with Polar Bears.
Old 04-13-07, 12:04 AM
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Originally Posted by kvrdave
Take a balloon and make an equator around it. Anything north or south goes around in a tighter circle, and would be relatively faster to the equator. At least, that is the way I read it.

But that should be slower, shouldn't it?
If youre on the equater you should be moving faster than if you're at any point north or south of it because if you're ont he equator you have to travel a further distance then than any other point on the globe to make one rotation.
Old 04-13-07, 08:41 AM
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Originally Posted by Mopower
Forget it.
Done.

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