# How would this work

1. Jan 30, 2006

### vincerelli

if you were to drill a hole through the center of the earth and line the whole with a material that made everything stay out of the hole (The bottom line is a clear path from one side of the earth to the other) and you fell down the hole what would happen. I would think you could not escape gravity's pull on the other side, if that were the case would you turn into a tight compacted ball when you finally settled in the core of the earth? INTERESTING!!!

2. Jan 30, 2006

### daveb

Neglecting air drag, you'd (roughly) fall to the opposite side, and oscillate back and forth between the openings. I say roughly because density of the surrounding material causes slight variations in the gravity field. With air drag, you'd oscillate several times back and forth, but not as far each time, until you settled in at the center of earth's gravity. Of course, this all assumes you drill through the actual center of gravity. Otherwise you slam into the side. No matter what, though, you'd end up dead from all the heat and radioactivity down there. Not sure how much the air pressure would be down there either.

Edited to add: I don't think the gravity is strong enough to compact you into a ball, btw.

3. Jan 30, 2006

### HallsofIvy

If you do allow for air resistance, then you would eventually come to a stop at the center of the earth- where the gravitational pull would, in fact, pull on you and not "compact" you.

4. Jan 30, 2006

### vincerelli

but, how would a force like gravity pull you when in fact there would be a force pushing you from both sides. I don't understand how it would pull you, well I guess if you were standing up (not really standing) your head and feet would be drawn to your waist.

5. Jan 30, 2006

### Claude Bile

Provided the hole is cylindrically symmetric, all the lateral forces would cancel out, the only remaining forces would be along the axis of the hole. The symmetry effectively reduces the problem to a 1D simple harmonic oscillator. If you consider the presence of air, the system becomes a 1D damped simple harmonic oscillator.

In the case of a damped oscillator you would indeed come to rest at the centre of the Earth, however the gravitational force at the centre of the Earth is exactly zero, because for each chunk of matter pulling on you, there is another chunk of matter pulling in the opposite direction with exactly the same force (This too is a consequence of symmetry).

Claude.

6. Jan 30, 2006

### moose

vincerelli, gravity pulls, not pushes. If there is an equal amount of matter all around you, then gravity will essentially cancel out.

7. Jan 30, 2006

### DaveC426913

Vincerelli, you weigh the most at the *surface* of the Earth. As you descend into the Earth, you'll weigh less. At the bottom of the Mariana Trench (the deepest spot on the Earth's surface) you would actually weigh slightly less than you would a sea level.

Why? Because there is slightly less "Earth" under you, and slightly more above you. It is enough to make a difference (but the geometry is diffilcult to explain). The upshot is that, by the time you reach the Centre of the Earth, you will feel zero gravititatonal pull. You will be weightless. The Earth's mass is actually pulling you outward, but it pulls out in all directions equally, and cancels out. (No, you won't feel pulled apart, either)

BTW, in all that falling thing, don't forget that the Earth turns. This ultimately ruins the experiment, since you can't use a straight tunnel. In fact, you can't just simply use a curved tunnel either, because you won't even fall back down the *same* tunnel you rose through. The tunnel you'd have to carve out would have a separate path for every trip from surface through core to surface. The tunnel would look like a spirograph design.

Last edited: Jan 30, 2006
8. Jan 30, 2006

### tony873004

You could drill from pole to pole.

Question. Imagine a hypothetical water world; pure water from surface to core. What would the pressure in the middle be? Gravity is cancelled but it seems to me like there would still be pressure from 4000 miles of water on top of you from all directions.

9. Jan 30, 2006

### nbo10

I think there is a train based on this concept, I can't remember where.

10. Feb 1, 2006

### Staff: Mentor

While your weight at the center of the earth would be zero, the weight of all that water crushing down on you would exert a very high pressure.

11. Feb 1, 2006

### pallidin

In this scenario, one would expierience acceleration towards the center of the earth. Likely, that acceleration would provide for your being ejected from that center point and further along the "tube"
Having reached a certain point due to acceleration, you would fall back past the center of the earth, though much less a distance than started.
In effect, as presented earlier, a "dampening" scenario would take-over, and thus eventually cyclically "vibrate" to a static equilibrium with the earth's center.
There is nothing special about it. This acceleration/oscillatory/damping effect is readily seen with metal springs.

12. Feb 1, 2006

### pallidin

Agreed. Also, gravity CANNOT be "canceled", however, it's objective influence can be mitigated.
For example, for someone to suggest that being in a hollow sphere in the center of our earth "cancels" gravity is simply not correct(not speaking to you or anyone in particular). Rather, under that scenario, there are external, spherical equipotental gravital influences which locally cancels out the influence, but not gravity itself.

13. Feb 1, 2006

### DaveC426913

I was trying to avoid implying that you would be "pulled apart" - eg. your left arm and right arm pulled in different directions. - this is not the case In fact, every part of your body is pulled in every direction.

As far as I know, except for gravitational tides (i.e. gradients over a distance), there is no way to detect this "pull in all directions", and for all intents purposes they really do cancel out. I may be wrong about that. Perhaps you can enlighten me.