If it were possible to dig a hole straight down, through the centre of the earth....?

Question

......then out through the other side of the earth and then you jumped down it, would you fall straight through to the other side of the earth? Would gravity take over in the middle of the earth and you'd be floating?

Answer 1

Bungee Jumping.

So, you jump off a bridge and hurtle down, bounce up, hurtle down, bounce up etc etc and so forth, but each time you hurtle down and bounce up it is a little bit less until you stop altogether.

And this is what would happen if you jump in your hole (presuming you are wearing something that will stop you being roasted alive after going down just a few hundred yards) You'd hurtle down head first, your head would just pop out in New Zealand for a split second before you went hurtling back etc etc etc

After about 17 years you would come to a full stop bang in the middle.

Unfortunately, in that 17 years there has been a lot of complaints about this hole that is going through the Earth, and it will be decided to fill it in.

Meanwhile you are in the middle, dead still, calling out "HELLOOooooooo" and very, very hungry. The air cannister on your back was only meant to last 18 years but you've been screaming so much that you've used it up too quick and things are getting a bit stuffy, and warm.

After all, that protective suit was only supposed to last for 10 years and you've been gone 17, so you can't really complain - not that there's anyone you can complain to because the telephone cable attached to you snapped on your 21st plunge.

Another thing we have to take into account.
Have you noticed that when you dig a hole in your garden you are left with a mound of earth at least twice the size of the hole?

That's because the pile of earth is not so compact as it was in the hole. So, this hole that went through the Earth . . . ?

So now Mount Everest is only a stepping stone to the top of your pile.

And who dug it?
Probably two Irish men with shovels and picks.
One started in England the other in New Zealand.

IF they met in the middle . . . . aw, it just goes on and on doesn't it?

Tell you what - let's build a tower up to the moon instead!

Answer 2

kuiperbelt2003 has the closest to the correct answer.

Gravity _decreases_ as you approach the earth's center. This is because, once you're under the surface, some of the earth is pulling UP on you and some is pulling DOWN on you. In the exact center, the pulls from all sides cancel out, and you are essentially weightless.

However, that doesn't mean you'll STOP there, because all the while you're falling toward the center, you're also building up momentum. By the time you reach the center, you're going at thousands of miles per hour, and your momentum just whooshes you through.

As you pass the center and make your journey toward the opposite side, gravity gradually increases again. This slows you down, but it does not completely stop you until just about the time you reach the opening on the opposite side. At that point, you'll stop, turn around, and fall back. In the absence of friction, you'll continue this back-and-forth motion indefinitely.

kuiperbelt2003 said the round trip would be 88 minutes. This would be true if the earth had a uniform density throughout its interior; but it doesn't. Because it's denser at the core than at the surface, the actual time would be somewhat less than 88 minutes.

EDIT:
GOD wrote:
> when you fall you reach a terminal vertical velocityof 120mph,you cannot fall faster than this speed VERTICALLY.

You're right. If you assume that the hole is full of air, and you consider the air resistance, then you would stop accelerating after you reached about 120 mph. Furthermore, you would slow down as the gravity decreased as you approached the center. You would still have some residual motion when you reached the center, which would cause you to "overshoot" the center; but after a few wobbles back and forth, you would end up stuck at the center. My analysis assumed an ideal condition of no air inside the tunnel.

> i see your point where you could have less gravity pushing you as youre beneath the surface but surely this would mean that you decelerate as you travel not accelerate.

No. As long as the net force points downward--in spite of the fact that it continually decreases in magnitude--you continue to go faster and faster downward. This is a simple consequence of Newton's laws of motion. As you point out, air resistance throws a monkey wrench into this; but if you ignore air resistance and assume that the only force is gravity, then you indeed continue to accelerate downward even when the downward force is continually decreasing. (You would only DEcelerate if the force were pulling BACKWARDS on you.)

> where you guys bring satellites into it,i dont get the correlation because a satellite is in a friction free environment.

Again, you're right if you assume air friction (which is the more realistic situation, probably). If you _ignore_ air friction, AND you assume that the density of the earth is uniform, then it turns out that the period of oscillation of the projectile in the tunnel is exactly equal to the orbital period of a low-earth orbiting satellite.

Answer 3

Provided that you're not crushed by the pressure, and that there is no air friction when you jump - then yes you'd fall straight thru and just barely reach the other side. - Because gravity will accelerate you to the center, and then decelerate you when you approach the other side of the earth. Unfortunately, you do know that the center of the earth is made of molten chocolate, though, right?

Answer 4

kuiper & Rick have their heads screwed on straight. As a first (and fairly accurate) approximation, the earth is constant density and the object dropped down the hole will behave according to Hooke's law:
k = mg/Re where Re is the earth's radius, 6376 km

The resulting harmonic motion has ω = √(k/m) = √(g/Re) = .0012398 rad/sec and
T = 2π/ω = 5086 sec = 84.5 min

Vmax (at the center) = Re*ω = 6.376E6*.0012398 = 7905 m/s. About Mach 23.........

NB: You would feel weightless the whole time. If there were friction involved, you would eventually stop at the center and feel no gravitational 'pull' at all.
Even more interesting is that the hole does NOT have to go through the center of the earth. The round trip time (period) will be the same. Only the velocity will differ.

Answer 5

If you were to construct such a tunnel and fall into it, you would experience oscillatory motion; you would fall through to the other side of the Earth, stop momentarily, and then begin to fall back through the tunnel again. Ignoring frictional effects, you would continue in this manner forever, executing the same motion as a block on the end of a frictionless spring.

In fact, your period of motion would be 88 minutes, the same period as a satellite in low Earth orbit.

If you work out the mathematics of this situation, you will find that the force the Earth exerts on you has the same form as Hooke's Law, the law that describes the motion of a mass on a spring.

Answer 6

I think you'd be boiled by the molten lava and heat of earths middle magma - whatever its called. So what I am trying to say is you would come out the other side the way cookie dough goes through a bakers oven - cooked!

Answer 7

Its not possible to dig right through as you would need to go through the earths core and it;s a bit hot there.

Very interesting about how gravity would work though. Presumably, it would work as you implied. You would stop falling at some point as you cannot go down any further and would be falling upwards, which can't happen.

Answer 8

you would be suspended in the middle just like an invisible bungee jump,of course its impossible though but if it were then that is what would happen.


kuiperbelt2003 is wrong,that would happen if no friction and pressure and based on the unknown fact that the earth is solid iron in the centre,why give a factual answer if you are going to omit a known force that will contribute to a totally different answer,tell the answer as it is if you're gonna be smart about it,cheers
88 minutes my foot
is that pole to pole or equator to equator,plus the other numerous variables to take into account.



ok rickb below :how do u work that out... when you fall you reach a terminal vertical velocityof 120mph,you cannot fall faster than this speed VERTICALLY.ie if you jump out of a plane at 20 000 ft you reach the same speed as if you jumped out of a plane at say 10 000 ft you dont keep on accelerating into infinity,.......right with that sorted you can say that the distance to the centre of the earth is 4000 miles or thereabouts ,with that in mind you can do simple maths to work out the journeys time.
remember rickB with your physics degree that this is a totally hyperthetical question,ok i see your point where you could have less gravity pushing you as youre beneath the surface but surely this would mean that you decelerate as you travel not accelerate to thousands of miles per hour,also where you guys bring satellites into it,i dont get the correlation because a satellite is in a friction free environment.having a physics degree myself is irrelevant to this as its an unproven theory like the existence of god.feel free to carry this on.

Answer 9

The question is hypothetical because it is not possible to do that. The earth's core consists of magma (that's molten rock, more or less) in which you would just evaporate - so your jump would be quite short. You'd be reduced to gas in a few seconds.

Answer 10

sky divers can ony reach 26 feet a second.
with that momentem once you reach half way and still against air resistance (and now with gravity against you)how far will you get?

if you could drill the hole it would fill with magma and when you jump in...

the planet is slightly egg shaped (slightly) if you jumped in the big end you might come out the other.
lol ;)