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22 replies to this topic

### #11 bonanova

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Posted 12 November 2010 - 05:51 AM

Imagine the earth is split into two halves. you are on one half at the very edge of the half.
if you jump off the edge:

how far do you fall before you stop falling?
Which way do you fall? down up sideways?

Spoiler for It depends on a few things

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### #12 Tsopi

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Posted 12 November 2010 - 08:19 AM

Thats a prety damn quastion.But let me tell you what i think.If the earth was ripped in half then something realy huge must have happened.I don't think that
the earth would still keep on turning but the two half would bang with each other and crash eventualy seperating or getting back in one piece.But with all this
happening where would the magma go?A realistic answer is not possible for me.But if we suppose that we have a controled situation of two semispheres
one next to another i can suppose that: (I am not really good at this but someone else might find it)
Calculate the speed somone will reach when he reach the earth centere (About 6,360 km radious) with m*g*h
Then calculate how far will this person go, considering the negative force applied on him by earth.
If the person with the speed he aquired won't be able to get out of earths atmoshpere he will fall back and he will travel less distance each time
eventually being stabilized in earths centere and (propably) stay on air on the total center of the earth
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### #13 Brain Tickler

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Posted 12 November 2010 - 02:56 PM

OK, first off, the guy would more than likely be crushed by increasing gravity towards the center. And probably pass out before that. But, for shitz and gigglez, let's just say that the guy falling is invincible. He is superman without the flying and kryptonite weakness. And for all these sick guys who have to get into the incineration and molten lava-_-, lets say it's a hole through a spherical object the size of the earth that has no molten lava. Depending on the aerodynamics of the person falling through the hole, they may reach a speed where, after "bouncing" from one end of the hole to another, they end up in the very center of the hole in a state of suspension. Theoretically, if they happen to have perfect surfaces that would cause no resistance, they may be able to reach a velocity and speed that could "slingshot" them through the other side and into the vast reaches of space. If this where the case, they would continue until they hit something or are smashed into by a passing space rock of some sort.
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### #14 bonanova

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Posted 12 November 2010 - 03:54 PM

Theoretically, ... they may be able to reach a velocity and speed that could "slingshot" them through the other side and into the vast reaches of space. If this where the case, they would continue until they hit something or are smashed into by a passing space rock of some sort.

If that were true, the space program could be run without resorting to rockets.
What a fuel savings!

It requires energy to lift an object at rest above the earth's surface.

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### #15 k-man

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Posted 12 November 2010 - 04:45 PM

If that were true, the space program could be run without resorting to rockets.
What a fuel savings!

It requires energy to lift an object at rest above the earth's surface.

That's correct, but if we had the ability to "orbit" inside the earth around it's center of gravity then we could use the slingshot effect to send rockets into space with a lot less fuel than we need now.
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### #16 d3k3

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Posted 12 November 2010 - 05:43 PM

That's correct, but if we had the ability to "orbit" inside the earth around it's center of gravity then we could use the slingshot effect to send rockets into space with a lot less fuel than we need now.

You can't get a gravity-assist from an object you are already either orbiting, or on the surface of. You have to intersect with an object from a different orbit to gain or lose energy from it.

There is a reason, however, why launch sites are always as close to the equator as politics and geography will allow, and why the first maneuver is always to head east(ish)...
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### #17 k-man

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Posted 12 November 2010 - 06:13 PM

You can't get a gravity-assist from an object you are already either orbiting, or on the surface of.

Correct, because you generally can't get "inside" the object. However, consider a rocket on the surface of the earth that can begin its acceleration toward the center of the earth using earth's gravity. It's not much different than a rocket approaching a gravity field of a planet from the outer space.
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### #18 d3k3

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Posted 12 November 2010 - 06:36 PM

Correct, because you generally can't get "inside" the object. However, consider a rocket on the surface of the earth that can begin its acceleration toward the center of the earth using earth's gravity. It's not much different than a rocket approaching a gravity field of a planet from the outer space.

No, it still doesn't work. You're only converting potential energy into kinetic energy. You're not gaining anything. The simplest example of a gravity-assist I can think of is analogous to a Hohmann Transfer:

Imagine that you're in a low-Earth-orbit (LEO), and want to instead be in the same orbit as the Moon. You could use a Hohmann transfer. The first burn (perigee kick) puts you into an elliptical orbit that is tangent to both the initial (LEO) and final (Moon) orbits. The second burn (apogee kick) gives you the remaining energy required. However, you could do away with the apogee kick and simply collide with the Moon.

Other, more complex maneuvers are possible (e.g. the Mariner and Voyager missions), but that's the general idea.

Note that the free energy comes from the Moon, not Earth.

Edited by d3k3, 12 November 2010 - 06:38 PM.

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### #19 k-man

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Posted 12 November 2010 - 10:30 PM

No, it still doesn't work. You're only converting potential energy into kinetic energy. You're not gaining anything. The simplest example of a gravity-assist I can think of is analogous to a Hohmann Transfer:

Imagine that you're in a low-Earth-orbit (LEO), and want to instead be in the same orbit as the Moon. You could use a Hohmann transfer. The first burn (perigee kick) puts you into an elliptical orbit that is tangent to both the initial (LEO) and final (Moon) orbits. The second burn (apogee kick) gives you the remaining energy required. However, you could do away with the apogee kick and simply collide with the Moon.

Other, more complex maneuvers are possible (e.g. the Mariner and Voyager missions), but that's the general idea.

Note that the free energy comes from the Moon, not Earth.

Even if the pure slingshot without using the engines is debatable in this scenario you could definitely use the Oberth effect to dramatically reduce the amount of fuel needed to launch rockets into space. The rocket could accelerate from the surface toward the center of the earth without burning any fuel at all and then fire its engines when it reached the center. It could then achieve the escape velocity using a lot less fuel than would require in a conventional launch.
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### #20 EventHorizon

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Posted 13 November 2010 - 01:18 AM

OK, first off, the guy would more than likely be crushed by increasing gravity towards the center. ...

The air pressure would increase as you get closer to the center, but gravity would decrease. I think you are probably thinking of Newton's law of universal gravitation, but that assumes point masses. For instance, if you are at the center of gravity of the earth, then there would be no force of gravity since there would be matter pulling almost equally in all directions... canceling the forces out. Using the equation directly, however, you'd instead expect infinite gravity... but I don't think we've collapsed into a black hole yet (though I could be wrong...).
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