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Sunday, July 20, 2014


Babson Geophysical Globe. U.S. Merchant Marine Academy. Schuyler Otis Bland Memorial Library. Kings Point, New York.

I have a globe. It is slightly larger than normal with a diameter of 16 inches. It is nowhere near as large as the Babson Globe shown above, but I like it. I'm thinking I should make some kind of mounting for it, and I got to thinking that maybe I should fill it with concrete so as to give it a more realistic feel. Set something like that to spinning on good bearings and it might be days before it came to a stop.
    Then I got to wondering just how much a scale globe should weigh, so I did some checking. Here's what I found:
  • density of granite:   170 pounds per cubic foot
  • density of steel:     500 pounds per cubic foot
  • density of the Earth: 345 pounds per cubic foot
So the density of the Earth is midway between that of granite and steel. That makes a certain amount of sense. So how much would a scale model globe weigh with the same density as the Earth?
  • typical 12" globe:                   180 pounds
  • my extra large 16" globe:            425 pounds
  • Babson globe (7' 6" in diameter): 76,000 pounds
Then I got to thinking about the biosphere, the portion of the Earth where there is life, and I realize it's like the skin of a balloon, pretty damn thin, and fairly insubstantial. There are also some fairly sizable holes in it, like deserts, high mountain ranges and the polar regions. Our small size gives us a limited view, and gravity keeps us glued to the surface. Even though some of us have our eyes on the stars we are really all flatlanders.


Anonymous said...

So how high would Everest be on those 3 scales? How thick the atmosphere?

Charles Pergiel said...

On the Babson globe Mt. Everest would be one sixteenth of an inch high. On the smaller globes it would only be a few thousandths of an inch. 50,000 feet of atmosphere on the Babson globe would be about one eighth of an inch. ISS would be almost three inches from the surface.