# If there was a tunnel from the north pole to the south pole

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Question: if there was a tunnel from the north pole to the south pole, then we threw anything in that tunnel, where will this thing go ?!!!

Is that thing will come out from the other side? or will stop in the middle?

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Air drag will slow it down considerably, so it won't come out the other side. Your object would also melt.

However, if you managed to pull the tunnel vacuum, and you manage to avoid the object hitting the sides of the tunnel, your object would get close to the south pole. However, the south pole is 2,835 metres above sea level, while the North pole is at sea level, with the ice only a couple of metres thick. This means that your object would be almost 3 km short.

Reversed, dropping an item in at the South pole, it would shoot out the North pole at considerable speed.

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Air drag will slow it down considerably, so it won't come out the other side. Your object would also melt.

However, if you managed to pull the tunnel vacuum, and you manage to avoid the object hitting the sides of the tunnel, your object would get close to the south pole. However, the south pole is 2,835 metres above sea level, while the North pole is at sea level, with the ice only a couple of metres thick. This means that your object would be almost 3 km short.

Reversed, dropping an item in at the South pole, it would shoot out the North pole at considerable speed.

There's an interesting video on that too.

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Reversed, dropping an item in at the South pole, it would shoot out the North pole at considerable speed.

Although, in both cases, it would fall back again and oscillate about the mid-point. With air resistance it would eventually stop in the middle. (This ignore imperfections, the rotation/precession of the Earth, the heat at the centre, etc.)

An interesting point is that it would take the same time to fall through and out the other side as an object in orbit (at the same starting altitude).

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Question: if there was a tunnel from the north pole to the south pole, then we threw anything in that tunnel, where will this thing go ?!!!
Is that thing will come out from the other side? or will stop in the middle?

My math professor described what he called the Wexler mail system.

With frictionless holes through the earth between cities around the world, you could drop your letter in a hole and not only would it come out on the other side of the earth, the time it takes is the same for all holes.

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Frictionless is the key. It can't avoid the sides...the darn Moon makes sure of that.

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Certainly the assumption exclude air, Friction, heat, and sea level.

The question is about the behavior of gravity .

It seems that the correct view is: in the end it will stop in the middle.

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Certainly the assumption exclude air, Friction, heat, and sea level.
The question is about the behavior of gravity .
It seems that the correct view is: in the end it will stop in the middle.

Not if you exclude air and friction

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I think get thus:

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I think get thus:

Not if you exclude friction and air resistance.

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Not if you exclude friction and air resistance.

For the same reason planets continue to orbit?

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For the same reason planets continue to orbit?

Exactly.

Although that raises an interesting question about whether tidal forces or general relativistic effects (frame dragging?) need to be ignored as well.

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However, if you managed to pull the tunnel vacuum, and you manage to avoid the object hitting the sides of the tunnel, your object would get close to the south pole. However, the south pole is 2,835 metres above sea level, while the North pole is at sea level, with the ice only a couple of metres thick. This means that your object would be almost 3 km short.

Reversed, dropping an item in at the South pole, it would shoot out the North pole at considerable speed.

I had always understood that the physical centre of the earth was not quite the same as the gravitational centre, and that there was a 20 km difference. I can't find any reference to this - but if correct, this might alter the response above.

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For the same reason planets continue to orbit?

And assuming you could put an object in orbit around the Earth at just above the surface, it would complete 1 orbit in the same time as the dropped object would take to complete a round trip.(Under ideal conditions: Spherical Earth of uniform density, no friction or air resistance, etc.)
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(Under ideal conditions: Spherical Earth of uniform density, no friction or air resistance, etc.)

And the "object" was a spherical cow of near zero mass.

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I had always understood that the physical centre of the earth was not quite the same as the gravitational centre, and that there was a 20 km difference. I can't find any reference to this - but if correct, this might alter the response above.

It would indeed alter the response if the difference was along the North-South axis. I would be surprised if it is that large, because I would think only the crust can cause such a difference and the influence of the crust is rather limited. I could be wrong.

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