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#1
Ok so I have a question thats been bugging me for a while now. Basically, I've been considering the effects of gravity. So I have a wonderous hypothetical situation for you all.

Someone somewhere has drilled a tube from the north pole to the south pole. It is invulnerable to all effects of heat, collapse etc and is a vacuum (basically the only force to consider is gravity). My question is, if I were to jump into the tube at the North side, what would happen?

I can see 3 potentials.

1. I would reach the centre of the Earth and stop.

2. I would go beyond Earths gravitational centre and shoot out of the tube at the South side.

3. I would stop just short of the South side and then fly back towards the North, continuing in a bunjee motion until I stop at the centre

My bet is on No 3 but I want to see what the Pit has to say.

(For the young and ignorant: The Earth's core is its centre of gravity)

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(the large circle is Earth and the smaller one is the core. I'm not falling through a doughnut...)

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#3
If that core is still there, then you're jumpin' into magma hombre.
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A SIGNATURE.
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#4
I think I've read that you'd just about make it to the end (albeit after a long time), but I don't know how accurate that is.
#5
I believe you would fall all the way down to the centre, and slowly be compressed into a tiny, itty bitty ball of CoffeAndJack.
#6
You would be crushed in the middle. Gravity doesn't just work going North and South. You have gravity pushing on you from all directions.
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#7
Number three.
Your momentum would speed you past the core a bit while gravity would slow you down, then negative feedback loop until you stop.

Of course you'd be crushed too.
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#8
you will get crushed under the earth's massive pressure. Assuming you're indestructible, number three sounds correct.

The amount that you will fall past the gravitational center depends on your inertia. If you're not in a vacuum, then it's probably your terminal velocity times your mass, but I'm not sure.
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#9
You'd just die.
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#12
Quote by CoffeeAndJack
3. I would stop just short of the South side and then fly back towards the North, continuing in a bunjee motion until I stop at the centre

My bet is on No 3 but I want to see what the Pit has to say.

I think this. I can't say I know for sure, and I've never looked into it, but it makes the most sense to me. Assuming you would survive falling for that long and the intense pressure that I assume the center of the Earth would have, you would probably move somewhat like a pendulum. Without friction, a pendulum would go forever (I think, maybe there's more to it), and without wind resistance, you would go forever. But both are present, so you'd never make it quite as far to the other side.
#13
assuming the tube is hollow. your movement would mimic that of a pendulum in terms of speed. at the very north and south poles your velocity would be zero. at the center of the tube your velocity would be at a maximum (but your acceleration would be zero).

This is assuming no energy is lost to heat or friction. you would continue moving up and down forever.

if friction was taken into account then you would probably eventually stop in the center.
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Last edited by Wesseem at Dec 21, 2011,
#14
well, you'd be crushed to put it blunt, but if we want to pretend you wouldn't be at the core, you would begin to spin, as the core of the earth does, due to the gravity hitting you from all directions.
#16
Quote by DonGlover
If that core is still there, then you're jumpin' into magma hombre.



great band name...
#18
Quote by WantsLesPaul
all the gravity would get out because theres a hole in the earth

This, obviously.
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#19
This was a question on the AP Physics C exam when I took it! It's a good question. That was years ago, so I don't remember many specifics, but the correct answer is your #3. The exam question was not what would happen, but more specifically to write an equation describing the period of the motion. There was some calculus involved since there would be less gravity pushing you towards the center as you got closer to it. You can start with Newton's law of gravitation and do the integral if you're so inclined, or punch in numbers if you're not (suggested: surface of earth, halfway down, exact middle).

TL;DR: #3.
#21
Quote by Johnljones7443
You would come out the other end in approximately 42.2 minutes.

I like this answer because it was on Qi.
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#22
Well according to Newtons laws of something or other you should go (almost? diminishing returns i geuss) an equal distance from the core as you went to the core. I was never great in physics, maybe some one here knows more about the laws of physics governing forces.
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#23
Quote by Wesseem
assuming the tube is hallow. your movement would mimic that of a pendulum in terms of speed. at the very north and south poles your velocity would be zero. at the center of the tube your velocity would be at a maximum (but your acceleration would be zero).

This is assuming no energy is lost to heat or friction. you would continue moving up and down forever.

if friction was taken into account then you would probably eventually stop in the center.


p.s. I'm right because i was asked essentially this very same question on my MCAT


This.
#25
Number 3. Gravity will always toward the centre of the earth, so you'd eventually settle there. Probably after you swing back and forth a bit, working off that momentum you picked up falling...
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#26
3. Simple Harmonic Motion.

EDIT: You accelerate towards the centre until you reach it but you overshoot due to the momentum you've built up. You then come out the other end at the same height as you first jumped towards the centre of the earth and begin to accelerate back towards the centre. This happens infinitely if it's a vacuum, you don't ever stop at the middle because there's nothing making you lose energy.
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Last edited by Mr_Jubby_Jubs at Sep 8, 2011,
#27
I have a better conundrum for you all.

You have a balloon in a stationary car, and then you accelerate forwards in the car.

If you are sitting in the car will the balloon appear to either
a) Move fowards
b) Move backwards
c) Stay in the same position relative to the car
#28
I prefer the one about the lorry trailer full of birds, and the change in weight if they were sat on perches or flapping in the air and not creating a downward push on the chassis.
#29
Quote by Wesseem
assuming the tube is hallow. your movement would mimic that of a pendulum in terms of speed. at the very north and south poles your velocity would be zero. at the center of the tube your velocity would be at a maximum (but your acceleration would be zero).

This is assuming no energy is lost to heat or friction. you would continue moving up and down forever.

if friction was taken into account then you would probably eventually stop in the center.


p.s. I'm right because i was asked essentially this very same question on my MCAT



Came in here to say this.

And to ask why the **** they would put a question like that on the MCATs
sigh...
#30
Quote by alexmottram
I have a better conundrum for you all.

You have a balloon in a stationary car, and then you accelerate forwards in the car.

If you are sitting in the car will the balloon appear to either
a) Move fowards
b) Move backwards
c) Stay in the same position relative to the car

b... if no force is applied, it won't move, so it appears to be going backwards (hence, you're pushed against the seat when you accelerate)

To the birds flying in a lorry, this was tested on Mythbusters, I can't recall the result, but the weight should stay the same

OT: it's (as said many times before) option 3 if you can be done no harm in the tube...
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#32
If it's a vacuum you would be dead before you even reached the center.

Quote by Ahteh
If it's vacuum there's no pressure guys. I.e. no crushing.


I think.

Gravity works in a vacuum.
Last edited by MakinLattes at Sep 8, 2011,
#33
I agree with # 3 with whatever is left of you...of course, the air pressure is WAY more intense and would crush you to death, I think. It would also take a really long time.
#34
Quote by Ahteh
If it's vacuum there's no pressure guys. I.e. no crushing.


I think.

True, but as you pass through the centre the force of gravity from all sides would crush you in a second, since it's proportional to 1 over the distance from the centre of an object squared.
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#35
I think it would be fun for about five sec.....then you would shit yourself and start wondering why i did this....then you would start to feel so much presure you would be unable to breathe...your heart would not be able to beat. and eventually you would be crushed to death...your mass would go through with number three...but your mind would not......science......
I haz gotten gud
#36
If there was vacuum in the tube, then you would travel south of the centere tha same distance that you traveled to the centre. So you would stop just at the exit on the south pole, and get out there. If you didnt grab the gorund, you would fall back out and continue falling up and down indeffinately.
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#37
The earth's core is almost 4,000 miles from the crust. Imagine the pressure of being a mile or so underground in a mineshaft. 4,000 miles would be a hell of a lot of pressure. You can't breathe own if you're 4,000 miles above the crust, you'd need some kind of spacesuit in that tunnel.
#38
Quote by Wesseem
assuming the tube is hallow. your movement would mimic that of a pendulum in terms of speed. at the very north and south poles your velocity would be zero. at the center of the tube your velocity would be at a maximum (but your acceleration would be zero).

This is assuming no energy is lost to heat or friction. you would continue moving up and down forever.

if friction was taken into account then you would probably eventually stop in the center.


p.s. I'm right because i was asked essentially this very same question on my MCAT


The energy required to counteract gravity is more than the energy gained from momentum caused by gravity. Perpetual motion is impossible unless you're a cat with a butter-side-up slice of toast stuck to your back. It may also be possible for cats with their feet stuck to the buttered side of a slice of toast, but the RSPCA won't let me do that experiment. Since all that confusion when Schrodinger was both commiting animal cruelty and not committing animal cruelty at the same time, they tend to put a stop to anything involving cats and the laws of physics.
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