# A few exam questions

Hootenanny
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If we consider the earth to be of uniform density then once you go below the earth's surface the gravitation field strength decreases due to the decreased mass enclosed by the circumference formed by the distance from the centre. However, the earth is not of uniform density, it is more dense at the core, therefore, the gravitational field strength will still increase the closer you are to the centre of the earth.

Oh, ok... err, I can't really find the answers on google... what exactly should I search for?

I've tried searching for 'earth's radius different points' and such, but I still can't find a place that has at least an approximation of the distance form earth's centre to those points... anyone know a way to improve my search?

Hootenanny
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Just take the radius of the earth to be the mean radius:6 371 km The equatorial radius is approximately 6 378 km.

Ok so the mean radius is 6731km, while at the equator it's 6738km. How do I find the radius at the poles? I couldn't find it on google...

Hootenanny
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Polar radius is approximately 6,357 km. Try to refine your searches. I searched for "Polar radius of earth" and google gave me the answer straight away. Try to be specific in your internet search or you'll spend all your life dredging through useless information.

Yeah, that's true, polar radius would've been better... but I couldn't really find anything about the ocean floor radius(at the lowes point). I don't know, maybe I'm just not looking hard enough...

Hootenanny
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[PLAIN said:
http://www.whoi.edu/info/deepest-ocean.html][/PLAIN] [Broken]
According to the National Geographic Atlas, the deepest-known part of the ocean measures 10,924 meters [..] near Guam
Now, if you substract this from the mean radius of the earth, you should have a pretty good estimate.

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Yeah I was considering simply finding the lowest point and doing that... ok so...

6731 - 10.924 =

6720.076 km

vs

6375 km

So the polar radius is smaller? How strange, but of course if you look at the ocean directly beside the poles, isn't that automatically lower than the poles? Or is that polar radius in the ocean, while the deepest point is somewhere around the equator???

Hootenanny
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Yes, you are correct, I think what your teacher was after here is a qualitative answer on instinct, my advice in an exam would be to go for the deepest spot in the oceans option.. Nice to see we've kinda drifted from the topic again

So it's the strongest at the bottom of the ocean then? But the bottom for some reason had a greater radius than the one at the poles... and of course the ocean floor at the poles would be the smallest radius I think... I think I'm confused...

Hootenanny
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Byrgg said:
So it's the strongest at the bottom of the ocean then? But the bottom for some reason had a greater radius than the one at the poles... and of course the ocean floor at the poles would be the smallest radius I think... I think I'm confused...
The deepest part of the ocean refers not to the distance from the sea floor to the centre of earth; but rather the depth below the surface of the water.

Yeah I know that much, but wouldn't you automatically assume that the bottom of the ocean right next to the poles would be lowest? Assuming that the poles are closer to the center than the equator?

Hootenanny
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Byrgg said:
Yeah I know that much, but wouldn't you automatically assume that the bottom of the ocean right next to the poles would be lowest? Assuming that the poles are closer to the center than the equator?
The lowest point in relation to the centre of the earth is not necessarily the deepest point in the oceans.

Yes I know that much, because the deepest point could be right around the equator or something, right? But if you take the poles, I'd think the oceans next to them would be deeper than the poles themselves, after all the distance to the center doesn't vary greatly in this manner unless you look at the poles compared to the equator, right?

Hootenanny
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Byrgg said:
Yes I know that much, because the deepest point could be right around the equator or something, right? But if you take the poles, I'd think the oceans next to them would be deeper than the poles themselves, after all the distance to the center doesn't vary greatly in this manner unless you look at the poles compared to the equator, right?
Yes you are correct.

So the greatest distance would'nt really be exactly at a pole unless there was water there, right? I'm not too up on my geography... is it only the south pole that has actual land mass on it? Or does the north pole have some too?

Hootenanny
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My major point in this is that you would have no idea of these value or facts for your examination, nor would you be expected to. Therefore, the expected answer would be the deepest part of the ocean. And yes, only the south pole is a land mass. The arctic circle is floating ice.

The deepest part of the ocean where exactly? On all of earth? Or the one near the poles like I said?

Hootenanny
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The deepest part of the ocean (i.e. the greatest depth below the surface of the water) is the Marianas Trench in the Pacific Ocean, which is the point I discussed above.

No... ugh, it's kind of hard to explain my thinking here... The deepest part of the ocean is as you said at Mariana's Trench, in the entire world... but since the poles are closer to the center of the earth... wouldn't the deepedt point there be the one closest to the earth? I'm not debating what you said that is indeed the greatest depth below the surface of the water, but I'm simply saying that deepest area at the poles is likely the one closest to the centre of the earth... as you said however, this is not necessarily the deepest point in the water. Did that clear up what I meant? I'm not too sure if I wasn't being specific enough at first or what... but that's more what I was thinking.

Hootenanny
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