200 LB Man Question???

ERRORIST · 2004-12-18 18:46:55

Why does a 200 lb man at the north pole weigh only 199.5 lbs at the equator?

GraemeSkinner · 2004-12-19 04:09:12

Due to centripetal acceleration the man weighs a tiny amount less at the equator than at the pole.

Just curious, is Interplanetary transportation the right thread to post such a question?

Graeme

ERRORIST · 2004-12-19 07:43:08

Due to centripetal acceleration the man weighs a tiny amount less at the equator than at the pole.

Just curious, is Interplanetary transportation the right thread to post such a question?

Are you sure it is Cetripital force and not Centrifual force?
Centripital force is and inward force and Centrifugal force is an outward force. I think they have Cetripital force confused with Gravity in this case. There is an outward force (Cetrifugal force) trying to through the man off the planet but gravity his holding him down (the inward force) not Centripital force.

Is the atmospheric pressure greater at the poles than it is at the Equator since the poles are 13 miles below sea level at the Equator?

This may all lead to something about interplanetary travel.

GraemeSkinner · 2004-12-19 08:57:23

http://curious.astro.cornell.edu/questi … er=310]1st result from Google

Pretty much answers the question

Graeme

ERRORIST · 2004-12-19 09:14:25

Got all that. But, I think it should be called Gravity instead of centripital force. Anyways, since the Earth is squashed down 13 miles at the poles wouldn't this mean atmospheric pressure has also changed in those regions as compared to the Equator 13 miles higher?

GCNRevenger · 2004-12-19 11:36:14

Got all that. But, I think it should be called Gravity instead of centripital force. Anyways, since the Earth is squashed down 13 miles at the poles wouldn't this mean atmospheric pressure has also changed in those regions as compared to the Equator 13 miles higher?

Not really, no. The difference in gravity is so small that it wouldn't effect the atmosphere at all given the wind currents of the planet and solar effects.

ERRORIST · 2004-12-19 13:00:14

It would have to since atmospheric pressure changes with altitude. 13 miles difference in altitude should mean quite a difference in pressure.

GCNRevenger · 2004-12-19 13:21:09

No it doesn't, not compared to the entire Earth's diameter.

And what do you think a "weather front" is? It is a region of differing air pressure... no, the natural circulation of the Earth's atmosphere would eliminate any real difference in pressure.

ERRORIST · 2004-12-19 14:45:18

So lets see, if Mt Everest was where Mt Mckinley is we would not need oxygen bottles once we reached the summit?

GCNRevenger · 2004-12-19 17:33:19

I know where this is going... you will then want to build - *GASP* - a pipeline from the North Pole to the Equator, 12,000 miles or so, and put a turbine in it to make unlimited free energy that would easily power the entire world.

Don't even think about it

Shaun Barrett · 2004-12-19 20:11:22

Hi ERRORIST!
I suspect GCNR is right that you're looking for a way to tap limitless energy from a pipeline connecting the North Pole to the Equator.

If we look at the 13 mile difference in Earth's polar-versus-equatorial radius you mentioned, it turns out it's not quite as simple as it may look at first glance.
If you think of the Poles as being 13 miles lower than the Equator, and ignore every other factor, then Earth's atmosphere would tend to pool at the Poles. If that happened, the 13 mile differential would result in the atmospheric pressure at the Equator being approximately 35 millibars! People in Singapore, for example, would need pressure suits and oxygen supplies.
Clearly, this doesn't happen.

In reality, Earth's rotation not only causes the Equator to bulge, via the centripetal acceleration process, but also creates a bulge in the atmosphere by the same means, increasing equatorial atmospheric pressure by essentially the same percentage.
As GCNR, says, the main factors in atmospheric pressure variation are localised topography and convection from solar heating.
Have a look at these two global pressure diagrams for January:-

.. and July:-

While the pressure at the Equator is always around 1010 millibars, the pressure at the summer pole is generally lower than that at the Equator.
While it is true that the atmospheric pressure at the South Pole in winter can be 15 millibars higher, on average, than the pressure at the Equator, persuading such a pressure gradient to perform any useful work over a distance of 10,000 km is unfortunately completely fanciful and totally impractical.

Sorry, ERRORIST. Another interesting idea comes to grief on the altar of unyielding facts.

But keep thinking outside the square because you just never know ...

ERRORIST · 2004-12-19 21:30:30

While it is true that the atmospheric pressure at the South Pole in winter can be 15 millibars higher, on average, than the pressure at the Equator, persuading such a pressure gradient to perform any useful work over a distance of 10,000 km is unfortunately completely fanciful and totally impractical.

Is the same for the North pole also true?

GCNRevenger · 2004-12-19 21:37:50

More or less, yes. 15 millibars is such a small difference that it would be hard to measure much less exploit.

ERRORIST · 2004-12-19 21:59:26

Neat diagram of the Earth.13 miles is sure alot of difference. I am interested in what the 13 mile difference in elevation (pressure wise) at sea level at the equator is? Is the .15 MB equal to what the 13 mile difference of atmosphere would be at the Equator if you went up 13 miles at the Equator?

GCNRevenger · 2004-12-19 22:34:05

Thats millibars Errorist... 1 Bar is roughly normal air pressure, so a difference of 0.15 millibars is like 00.015% difference.

If THAT number doesn't convince you that your idea isn't worth your exertion, nothing will.

Shaun Barrett · 2004-12-20 07:12:32

Hi again, ERRORIST.
If you were to ascend vertically from sea-level on Earth's surface to an altitude of 13 miles, you would notice the atmospheric pressure drop from around 1013 millibars to only 35 millibars (not much more than 3% of normal). I mentioned this in my last post.
The reduction in pressure will be essentially the same no matter where on Earth you begin your ascent, be it from one of the Poles or the from Equator. An unprotected human exposed to an ambient pressure of 35 millibars will die an unpleasant death because, as far as the human body is concerned, it's as good (bad! ) as being in outer space.

The 15 millibar difference in atmospheric pressure between, say, the South Pole in winter (greater pressure) and the Equator (lesser pressure) is due to the extreme cold of the polar air causing it to sink because it's denser.
This 15 millibar differential represents less than 1.5% of Earth's normal sea-level atmospheric pressure - in other words, it's not much!
Meteorologists routinely see bigger differences from one side of the day's weather chart to the other as high and low pressure systems traverse your local area. And, to give you some idea of what Earth's atmosphere is capable of, the highest recorded atmospheric pressure was 1085.7 millibars, measured at Tonsontsengel, Mongolia, on December 19th 2001. While the lowest recorded atmospheric pressure, 869.96 millibars, occurred in the Western Pacific on October 12th 1979. (Courtesy Wikipedia.) The difference between these two figures ... a whopping 215.74 millibars!!

Constructing a pipeline from the South Pole to the Equator in an attempt to take advantage of a transient seasonal pressure differential of only 15 millibars, in the hope of generating electrical power from turbines, is an exercise in futility I'm afraid.
This pressure gradient, over the 10,000 km distance involved, comes down to a differential of 0.0015 millibar per kilometre of pipe. Friction between the air and the walls of the pipe itself would be enough to reduce any air movement to about zero - you'd have more chance of moving the turbine blades if you sneezed at them!
Sorry. It won't work.

ERRORIST · 2004-12-20 07:55:03

Thats millibars Errorist... 1 Bar is roughly normal air pressure, so a difference of 0.15 millibars is like 00.015% difference.

Yes it is small.
Is the .15 MB equal to what the 13 mile difference of atmosphere would be at the Equator if you went up 13 miles at the Equator,also?

GCNRevenger · 2004-12-20 09:50:26

Errorist, stop thinking about the elevation difference between 0 and 90 long. for a minute... We have already pointed out to you about four times now that this pressure difference is negligible.

In that case, a moutain on the equator and at the pole would have about the same air pressure as well.

ERRORIST · 2004-12-20 10:12:15

If you were to ascend vertically from sea-level on Earth's surface to an altitude of 13 miles, you would notice the atmospheric pressure drop from around 1013 millibars to only 35 millibars (not much more than 3% of normal).

Constructing a pipeline from the South Pole to the Equator in an attempt to take advantage of a transient seasonal pressure differential of only 15 millibars, in the hope of generating electrical power from turbines, is an exercise in futility I'm afraid.

If the diffence in these two altitudes are the same then why is there a huge difference in the millibars .15mb to 35mb??

Also, have they ever taken barometer readings from the ice pack at both the north and south poles?

GCNRevenger · 2004-12-20 11:11:28

Simple. The Earth's atmosphere circulates continuously, especially around the poles, which eliminates any large area scale air pressure differences. Hence, only localized (read: moutains, storms, etc) pressure effects exsist. The air simply won't sit and pool and cause a perminant pressure gradient, it is constantly being blown around.

We don't need to send barometers, satelites can do it.

ERRORIST · 2004-12-20 11:42:21

What if the air was not blown around?

GCNRevenger · 2004-12-20 11:58:10

And you propose to stop the winds of the Earth?

Wind cannot be eliminated on spinning planets, a natural consequence of the viscosity of gasses will dictate that the gasses are "dragged" along as the planet spins.

ERRORIST · 2004-12-20 12:08:32

No what if you placed some atmosphere in a long tube and confined it from blowing around?

John Creighton · 2004-12-20 12:16:18

No what if you placed some atmosphere in a long tube and confined it from blowing around?

You know strange but maybe he is right. If the spinning earth creates a pressure imbalance at the equator then maybe you could drop some of this air back with a pipe. The flow might be next to nothing but there still may be a flow there. ???

GCNRevenger · 2004-12-20 12:20:17

And maybe you are trying extra hard not to listen Errorist or John.

Nothing would happen Errorist. Not one thing. The very, very small difference in air pressure would be completly overwhelmed the resistance to motion due to viscosity. There would be no air flow at all. If all you do is seal one end of the pipe, that won't change the pressure anyway.

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Re: 200 LB Man Question???

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