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Re: Hypothetical Gravity Questions

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Posted by Bruce J. on April 28, 1997 15:37:39 UTC

: : : : Hello! I was wondering how much gravity our bodies can withstand before the effects of gravity become intolerable. The reason I ask is that it's obvious to me that the state of your body would start to deteriorate long before you even reached the event horizon of a black hole. Given that the farther you are from an object, the less the attraction there is between you and the object, what would be the safest minimum distance you could be to a black hole's event horizon without endangering your health?: : Well, the question you've posted is a little ambiguous. I assume by distance you mean standing distance(not flying away or racing toward).: : Any fighter pilot will tell you that nine G's and you lose conciousness(blackout) negative 3 G's and the same thing happens(red out): : On the other hand you might be fine with one Gee of acceleration jumping off of a twenty story building...until you hit the ground.: : Now, in terms of the sheering force of gravity as you approach the event horizon of a black hole, its reasonable to say that I have no earthly clue at what distance the effects would be detrimental, but I'm anxious to find out.: : Here's an idea. You build a scenario of some detail and I'll see if I can pick a few brains with nothing better to do. : : : Here's some more ideas. Consider a person in orbit around the earth; they are essentially weightless, because the centripetal: : acceleration away from earth as they orbit is exactly balanced by the gravitational force toward the planet. Now, picture the: : same thing around a black hole. If you can accelerate yourself (slowly!) to a high enough speed to remain in a stable orbit around a black hole,: : you would experience zero gravity and therefore no physical or mental distortion. depending on your distance from the singularity;: : however, your speed might be so high that you would experience relativistic effects (although you might not notice them), and if you get too close to the: : event horizon, you might not be able to correct for small changes and get sucked in! : : Hi, Bruce! I've read your comments in this forum and really like what you have to say. I'm curious: How do you know so much about black holes and physics in general? Now to my serious question: What is this centripetal acceleration AWAY from the Earth you're referring to? Isn't centripetal acceleration the acceleration TOWARD the center of a circle, not AWAY from it? Also, I thought that astronauts in orbit did in fact experience the Earth's gravity (Isn't it called microgravity?); it's just that gravitational attraction decreases with distance. Your ideas about orbitting a black hole seem sound, although we'd want enough gravity (9.8 m/s2 optimally) to retain the structure of our bodies. And we can easily correct our calculations for relativistic effects using Einstein's transformations. : Hello, Sarah - thanks very much. I took physics a long time ago in HS and college (I am a meteorologist by training), as well as studied some and read articles on my own, and now I'm being inspired to try to recollect it all! I have used the wrong word in the case of centripetal - which means the force that gravity itself exerts - for the outward force, centrifugal may be more correct. In any case, it the same force that allows any object to have a stable orbit around another, with gravity 'pulling' toward the larger object and the motion of the smaller object providing a force component away from the larger object.

: Also, yes, astronauts experience gravity in space, just slightly diminished from that at the earth's surface. But, they also experience the outward force component that allows them to orbit. In a sense, the astronaut in orbit is always falling toward earth, but their lateral velocity is enough to maintain their altitude as they fall, and therefore they remain in orbit. The same would hold true around a black hole, because gravitationally, a black hole behaves just like any ordinary planet or star of the same mass. It would be relatively easy, using the Newtonian model for gravity, to determine the separation required for an astronaut to achieve a G-force of 9.8 m/sec/sec near a black hole. The relativisitic effects would occur as the outside observer sees the astronaut hovering closer and closer to the event horizon; to each observer, the other would appear to experience time more and more slowly. There is a good link on these topics at Have fun! Let's talk some more...BJ

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