Gravity

Post by **Roofus** » Thu Nov 18, 2004 3:57 pm

Ok, imagine you had a very long drill bit, and you used it to drill all the way through the Earth. From where you are to the point 180 degrees opposite you. Clear through the center to the other side. Now imagein jumped into the hole. What would happen to you? I don't think you'd come out the other side, because for half the journey you'd be falling up. Would you just stay at the center?

Clessy · Post by **Clessy** » Thu Nov 18, 2004 4:09 pm

You'd more than likly stay in the middle if you couldnt actually die.

Matt · Post by **Matt** » Thu Nov 18, 2004 4:27 pm

That would be pretty weird

Midgey34 · Post by **Midgey34** » Thu Nov 18, 2004 4:41 pm

I say center because thats were gravity is pulling us all to after all right?

impetus · Post by **impetus** » Thu Nov 18, 2004 4:52 pm

you would be incinerated long before you hit center

hearld500 · Post by **hearld500** » Thu Nov 18, 2004 5:00 pm

That is a question. Assuming that the heat of the center of the earth didn't get you, and you could just fall, what would happen?

I'd bet that friction from the air would just slow you down to terminal volacity. You wouldn't make it up to the other side.

Without air, I have no idea.

Post by **Roofus** » Thu Nov 18, 2004 5:04 pm

impetus wrote:you would be incinerated long before you hit center

They also don't have drill bits that can drill all the way through the earth. Humor me.

DaMadFiddler · Post by **DaMadFiddler** » Thu Nov 18, 2004 5:05 pm

Depends on the environmental factors. Assuming the gravity reaches infinitely, and/or you're dealing with a full atmosphere, you'll probably settle roughly in the center because that's the focal point of the gravitational field.

However, given that the Earth's gravitational field gradually weakens as it extends outward, and if you assume the atmosphere doesn't have enough of a dampening effect, it could act as a cannon: you could theoretically build enough momentum falling down the one "side" that you'd be rocketed out the other and clear the gravitational field before you had a chance to slow down enough.

Of course, I'm not sure quite what the values of the relevant factors are. And you'd need to completely clear the Earth's gravity with the momentum built from the initial drop in order for option (B) to work. Otherwise, you'd either settle in the middle naturally, or fall back and forth in gradually decreasing heights until you eventually settled in the middle anyway.

Ex-Cyber · Post by **Ex-Cyber** » Thu Nov 18, 2004 5:06 pm

My guess is that it would be your momentum vs. Earth's gravitational field once you hit the center. Sadly I have no mathematical grounding in physics so I don't know how to calculate it, but it probably wouldn't be too difficult for someone who knows how to crunch Newton's laws. If the momentum has any notable effect I guess you'd swing back and forth past the center until you came to rest.

Post by **Roofus** » Thu Nov 18, 2004 5:09 pm

DaMadFiddler wrote:or fall back and forth in gradually decreasing heights until you eventually settled in the middle anyway.

That's pretty much what I think would happen.

Post by **Quzar** » Thu Nov 18, 2004 5:13 pm

the thing is that you would be accellerating at an increased rate as you approach the center (closer you are stronger gravity is). it would simply depend on wether or not you have attained a speed and accelleration by the time that you reach the center that you are able to break out the other side. If it was a perfect environment and you lowered yourself into the hole and dropped, then you should theoretically get to the cusp of the hole on the other side.

BlackAura · Post by **BlackAura** » Thu Nov 18, 2004 5:41 pm

However, the Earth's gravity isn't generated by a point source. It's generated by the combined mass of the entire planet, and doesn't have a focal point as such.

As you decend, would the force exerted on you by gravity actually increase? Say, you get a third of the way down. Ignoring the fact that you'd have melted long before then, you'd be much closer to most of the planet's mass, but you'd have a fairly large mass behind you (which is even closer) pulling you back the opposite direction, along with large masses all around you in all directions pulling you sideways.

Ender · Post by **Ender** » Thu Nov 18, 2004 5:43 pm

ACtually, if you do the math, you would oscillate from one pole to the other like a pendulum. Assuming the same mass/density ratio for either hemisphere, you would pop just above the surface, then go back and pop above the other surface, ad infinitum.

However, if there was a slight variation in the mass/density of one of the two hemispheres, you would slowly bob back and forth, eventually settling at the pole (after many years).

If there were a large variation, you would be slingshotted into the atmosphere on one of the sides.

Post by **Quzar** » Thu Nov 18, 2004 7:30 pm

BlackAura wrote:However, the Earth's gravity isn't generated by a point source. It's generated by the combined mass of the entire planet, and doesn't have a focal point as such.

As you decend, would the force exerted on you by gravity actually increase? Say, you get a third of the way down. Ignoring the fact that you'd have melted long before then, you'd be much closer to most of the planet's mass, but you'd have a fairly large mass behind you (which is even closer) pulling you back the opposite direction, along with large masses all around you in all directions pulling you sideways.

most reputable sources say that the earth gets denser as you get closer to the core, so you may be right that the net gravity would be decreasing, but not by much as the dense core would compensate for some of it.

Mr. Jones · Post by **Mr. Jones** » Fri Nov 19, 2004 12:44 am

I'm thinking that you would approach a point where the force of the earths gravitational pull would be to much for your body to handle, and you would explode. Its not like when you're on the surface, where the force is pulling in one direction, or when you're in water, where the mass of the body of water is pressing against you in all directions. you would reach a point where approximately 1/2 the gravity of the entire planet is pulling at you from all sides. I wouldn't think that the body could handle this type of stress, and would eventually explode.

My head hurts now.

area · Post by **area** » Fri Nov 19, 2004 1:38 am

The ratio of the mass in front of you and behind you as you fall into the centre will move from infinity to 1. This means (I think) that you'll always be accelerating as you fall into the centre. Only when you go past the center will you start decelerating becuase there is more mass behind you than in front of you.

When you reach the center, you have an equal mass in front of you and behind you, so acceleration due to gravity will be zero, so you'll continue at your speed.

You'll therefore decelerate on your way out, and will reach a speed of zero when you reach the surface on the other side.

That's just my take on it.

EDIT: I should read the topic. Ender basically already said this, although it assumes the planet has uniform mass, which is clearly a lie.

Ender · Post by **Ender** » Fri Nov 19, 2004 1:44 am

area wrote:The ratio of the mass in front of you and behind you as you fall into the centre will move from infinity to 1. This means (I think) that you'll always be accelerating as you fall into the centre. Only when you go past the center will you start decelerating becuase there is more mass behind you than in front of you.

When you reach the center, you have an equal mass in front of you and behind you, so acceleration due to gravity will be zero, so you'll continue at your speed.

You'll therefore decelerate on your way out, and will reach a speed of zero when you reach the surface on the other side.

That's just my take on it.

EDIT: I should read the topic. Ender basically already said this, although it assumes the planet has uniform mass, which is clearly a lie.

Yea, I actually have had this on physics exams. Mathematically, what I said is correct. In reality, well, you'd die before you got a couple kilometres down.

Ender · Post by **Ender** » Fri Nov 19, 2004 2:15 am

Mr. Jones wrote:I'm thinking that you would approach a point where the force of the earths gravitational pull would be to much for your body to handle, and you would explode. Its not like when you're on the surface, where the force is pulling in one direction, or when you're in water, where the mass of the body of water is pressing against you in all directions. you would reach a point where approximately 1/2 the gravity of the entire planet is pulling at you from all sides. I wouldn't think that the body could handle this type of stress, and would eventually explode.

My head hurts now.

Not sure if your whole body would explode from the pressure and G forces, but your eardrums would definately rupture really quickly. Gravity wouldn't pull you apart though, if anything, the acceleration would. But since I don't really feel like calculating the G's right now, let's just say that you'd be dead from lack of oxygen in no time, before hitting the lava.

All in all, with the eardrums rupturing, the asphyxiation, and the magma flow, it would be a painful, painful death.

mkjones · Post by **mkjones** » Fri Nov 19, 2004 11:30 am

Stupid question yes.

But you would simply "stay" at the center. Imagine for example earth was a Gas giant and this is possible, no drills needed, taking out pressure factors of course.

mattcky666 · Post by **mattcky666** » Fri Nov 19, 2004 12:28 pm

same as what everyone else has said, evenually you will end up in the middle however the speed at which you are going before you reach the middle will propell you upwards, however gravity will evenually slow you down and therefore end in the middle after going through the center a few times.

When ur in the middle, wouldnt you evenually "float" because gravity is supposely equally distributed to each direction of ur body and therefore ur weight would be 0.

(All in theory by the way)

(oh and sorry if neone else has mentioned this - i obviously didnt read it)