Posted on 02/10/2005 10:59:13 AM PST by vannrox
WTF ? a 30 meter BALL of melted iron is gonna weigh MUCH MORE.
Nope, the mass distribution and gravity is only perfectly cancelled at the exact center. Everywhere else inside the sphere you will get microgravity which will start you falling to the inner edge of the sphere.
Of course if that sphere is large enough, it's going to hurt when you hit the sphere.
Because as you approach any point on the wall, even though the material you are receding from exerts less and less gravitational force on you, there is more and more of it in that general direction?
Exactly.
RE: 108 kilograms, the amount of iron in a sphere about 30 meters in diameter.
????? Oooops! That's some pretty light iron there!
"Ok, zero g in the center of the earth, 1 g at the surface of the earth, and gets less and less the further you go out. What is the max g point?"
The maximum g point would be at the earth's surface, or 1 g. As one went beneath the surface, the pull would decrease until it reached zero g at the center. If the earth were hollow (which seems unlikely), it would reach zero g as soon as one reached the hollow cavity.
"Stevenson would start the process by finding a suitable fissure in the Earth’s crust, setting off a multi-megaton underground nuclear explosion to widen the fissure to a sizable crack, and then dumping in an instrumented blob of liquid iron (melting point 1535 C) with a mass of about 108 kilograms, the amount of iron in a sphere about 30 meters in diameter."
Something's wrong here -- a solid iron sphere about 30 meters in diameter would weigh more by a factor of about a million . . .
Cheap metals, potentially. The planet's interior to some degree acts as a giant smelter, and metals separate themselves, often with excellent purity.
If there were methods in place that allowed the efficient and inexpensive extraction of these metals, it could potentially make the United States an industrial economy again, exporting all the metals required to satiate world demand. :)
Additionally, if mankind became adept at underground engineering and construction, we lay the groundwork for innoculation from nuclear attack in the near term and a hostile environment long-term in the event of ice age, solar instability, or asteroid impact.
Wouldn't that cause an object located at any point inside the sphere to be drawn towards the center?
Carlos Castaneda fan? Did anyone ever find out if he actually knew someone named Don Juan?
If I were a bettin' man, I would take you up on that. It is true that since gravity follows the inverse square rule, gravity increases greatly as you approach the mass, but the aggregate of the gravity from the much larger mass in the other direction cancels it out when inside a hollow sphere. Picture yourself standing (if it were possible) on the inside surface of the hollow sphere. There is a very small mass pulling you down (under your feet), but the rest of the sphere pulling you up (everywhere else). Cancels out. Anybody else out there agree or disagree? Now, if the hollow sphere is John Kerry's cranium...that's a different story.
I'm scratching my head on this one.
I'm still thinking that an object will be drawn to the center, for the very reasons you point out. Once in the center, the mass distribution and gravitational force is equal on all sides, resulting in zero-G.
SF ping.
Physicist, what do you think? Zero gravity inside a massive hollow sphere?
Everything inside Kerry's hollow cranium tends to the left side...definitely not the center.
LOL!
Actually, that's incorrect. I proved it in an analytic geometry class in college. The gravity is exactly canceled out at every point inside the hollow sphere.
The reason for this is as follows: Starting at the center of the sphere, as you move to a non-central point (say, to your right), the gravitational attraction between you and the part of the sphere you're approaching increases...but you're putting more of the sphere behind you than in front of you, in a ratio and at a distance that exactly balances your proximity to the point you're approaching.
It sounds complicated, but it works. Honest.
I'm interested to see the proof, and I've got an open mind on this one at this point.
The cut-and-paste failed...the actual number was probably supposed to be 10^8, or 10 to the 8th power kilograms. Make it 100 million kilos of iron.
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