Increadibly large, hollow artificial planet

[formulaterp]

<font color="yellow">Text books for at least a century, teach that there is no gravity anywhere inside a hollow sphere in free fall. Perhaps they assume zero wall thickness or some other unreal condition.</font><br /><br />Actually it was first postulated in 1687 by Isaac Newton in <i>Principia.</i> And no assumption as to the thickness is made. The mass/thickness of the sphere is irrelevant, you would still experience weightlessness within the sphere. Of course there are practical considerations. As the mass of the sphere increases, it would collapse under it's own gravity.<br /><br /><font color="yellow">what would it be like to climb though a hole from the outside to the inside of a hollow sphere</font><br /><br />Interesting thought experiment. Of course if there were a hole to crawl through, then there would no longer be a zero-g environment within the sphere. I would imagine the net gravitational attraction would be to a point on the interior of the sphere, exactly opposite the entry hole.<br />

 

[formulaterp]

<font color="yellow">2d sphere...<br /><br />This relates to a hollow planet. A solid planet would have a center of mass as a point. on a hollow planet, the center of mass can be described as approximately halfway from where you are currently standing to the end of the mass, meaing that a person either on the outside or inside would trace out teh center of mass as a sphere. whos radius is large enough to coincide with the mid point of the mass as calculated from any one spot. </font><br /><br />I still don't understand this. The center of mass of a uniform hollow sphere would be it's geometric center. This would be a point, not a sphere (2d/3d or otherwise).

 

[valareos]

the neter of mass of a uniform hollow sphere CANT be its center, because there is no mass there to be the center of<br /><br />It may be easier to understand in this thought<br /><br />You know the way that gravity is depicted as a bowling ball on a rubber trampoline. it warps the rubber around it. <br /><br />Ok lets put it in the correct perspective of dimentions.<br /><br />the rubber sheet is space-time. we agree with this.<br /><br />now using a bowling ball is wrong (by the thought of perspective, that bowling ball would be a 5 dimentional object!) what should be used is a flat metal disk. (same effect, more akin to what is happening)<br /><br />Now, lets say we got a hollow planet. (this will be represented by a large heavy metal ring)<br /><br />What happens? a marble placed anywhere will be directed towards the metal ring, NOT the center of the ring, whcih now exists as a "bumb" in gravity.<br /><br />The center of mass is not the geometric center

 

[valareos]

pfft Im talkig about a ring the size of a hulahoop lmao

 

[nexium]

Wow, 1687. It may be centuries before we can test this postulate. If we had measured the gravity inside the 4 Echo ballons, and found a nano g,: It would surely be argued that the measurement accuracy is + or minus two nano g, besides the solar wind is causing an error of 3 nano g and gas leakage from the balloons a likely 1/2 nano g etc.<br /> If exact opposite a hole or low mass area of the sphere, then free falling objects (including air molecules) would fall toward and converge at that exact opposite point. Interesting thought experiment. Neil

 

[jatslo]

…Provided the planet is hollow… I sense “Intelligence” at play here, and any artificially constructed planet would undoubtedly generate artificial gravity; this artificial gravity would in affect make measuring gravity difficult by any means.<br /><br />There are too many unknown variables involved in the equation to reach a definitive conclusion, don't you think?<br /><br /><br />

 

[nexium]

We don't have many choices of real planet, near term. The gas giant planets have too much gravity in the cloud tops, and have nasty wind gusts. A few miles below the cloud tops the gas pressure is too high.<br /> Venus is too hot except near the cloud tops.<br /> Mars has bad dust storms and dangerous levels of radiation. Low each day is about 100 degrees f colder than the high. Mars may be our only planet to colonize. but the poles of Mercury should be considered. Negligible atmosphere, negligible magnetic field, but the bottom of polar craters are always in the shade and thus are uniformly cool and low radiation. At the top of the crater rim is high temperature 24/7 making for cheap energy sources. <br />The closest we can come to an artificial planet, near term is the ISS = international space station. I suppose an ion engine could gently get the ISS into solar orbit in about a year. At present we can't make a colony even close to self sufficient. Neil

 

[formulaterp]

<font color="yellow">the center of mass of a uniform hollow sphere CANT be its center, because there is no mass there to be the center of</font><br /><br />There doesn't <b>need</b> to be a mass there for it to be the center. Consider a binary star system. Where is the center of mass/gravity of the system? <br />

 

[valareos]

you are misreading that there. there are 2 centers of mass, one in each star. they orbit around a barycenter (ie, 2 masses orbiting around eachother. They still have their seperate centers of mass and centers of gravity.