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PileUp Officer
10th Apr 2006, 09:46
...if you dug a big tunnel through centre of the Earth to the other side and then dropped a (n asbestos) ball down it. Would it just float in the middle?

I asked in the pub last night but the yokels didn't know.

green granite
10th Apr 2006, 10:20
my guess is:

Eventually yes after many oscilations. i.e it would accelerate to the centre
then decelerate going "up" the other side and so on, each pass being a
of slightly smaller amplitude :8

tony draper
10th Apr 2006, 10:26
Nickle iron core me arse,there a black hole at the center of the earth,as there is at the center of all planets and stars,
Wouldn't the asbestos ball hit the turtle?
:uhoh:

green granite
10th Apr 2006, 10:29
Only if it forgot to duck :ok:

chornedsnorkack
10th Apr 2006, 10:31
OK, letīs give the answers:

If the tunnel is dug at any angle to the axis of Earth, then an object dropped in would deviate from vertical thanks to Coriolis force and hit the walls.

So, to exclude this effect, dig the tunnel at the axis of Earth, from South Pole to North Pole.

If the Earth were of uniform density throughout, any object dropped down its axis would accelerate to the first cosmical velocity at the center, decelerate - and reach the other end of tunnel (or more correctly, same height near its mouth - the South Pole is higher!) at the same time which is needed for a satellite to perform half an orbit.

However, Earth is not a sphere of uniform density. The density increases downwards.

Therefore a body dropped down the axis of Earth would accelerate to a greater speed, and reach the destination faster.

Of course assuming no friction. Say, there is deep vacuum in the tunnel...

If there isnīt a complete vacuum in the middle, then friction would slow down the body. Yes, if it is stopped completely in the centre, it would just float.

tony draper
10th Apr 2006, 10:39
Ah! but what of tidal forces from moon and suns gravity? would they not pull upon this hyperthetical asbestos sphere,thereby pulling it off center?
:rolleyes:

PileUp Officer
10th Apr 2006, 10:45
Ahh, I see the thread has gained critical mass.

No-one seems to ever want to make the first post in a new thread but once the replies start then everyone jumps in :)

BlueWolf
10th Apr 2006, 10:45
The folks wot live beneath would chuck it back, and most likely come out to bite yer, so don't try it.

Read an account once about a French (I think) scientific chappie who dug two shafts, a mile deep and many miles apart, and hung thingumybobs down them, and measured the angles of the hangles, as it were, so as to calculate the centre of the earth's gravity.

Apparently the thingumybobs swung the opposite way to what was expected, and the centre of the earth's gravity is thus supposedly 4000 miles out in space.

It makes a kind of sense, in quantum terms anyway, and if you can ignore the French connection. Anyone heard of this?

Ultranomad
10th Apr 2006, 11:27
Bluewolf, local gravity anomalies are fairly common. Gravimetry (measurement of gravity magnitude and direction) is routinely used by geologists to assess the density of rocks. A very long pendulum you described would deviate from the vertical direction towards denser rocks.

BlueWolf
10th Apr 2006, 11:29
You're right about gravitational anomalies, I've got one in my bathroom, right underneath the scales :*

Gouabafla
10th Apr 2006, 11:51
What would happen if you put conveyor belt in the tunnel?

tony draper
10th Apr 2006, 11:56
One thing is certain that tunnel woud not be open five minutes before hordes of refugees and illegal imigrants started flooding through.
:uhoh:

G-CPTN
10th Apr 2006, 12:02
You'd NEED the conveyor to get the spoil out of the tunnel.

Tricky Woo
10th Apr 2006, 12:16
Shame the Victorians didn't have a go at building one. Never shy when it came to engineering triumphs, yer victorians. Not like today, where we get all excited about some Channel Tunnel, or the Jubilee Line extension. Pah! Brunel could have dug those out in a month with his 20,000 Irish navvies armed wi' nowt but the sweat on their brow and rusty spoons.

Would have saved a lot of time and trouble transporting them guests of Her Majesty to the southern colonies. Very useful, indeed. Population of Australia would be a lot bigger than it is now, and vice versa. Nevermind transporting the riff-raff for stealing sheep, they could have lowered the bar to include anyone with so much as a bad haircut for relocation. And that would clear out the scousers, for a start.

Where were we?

Hmm, methinks that gravity is neutral (or close to it) at the centre of the earth. The ball should indeed whizz through the centre, nearly up to the top of the shaft at the prison end, and then back to the Blighty end only less far again. So on, and so forth until it settles in the middle.

Now one only needs that clever ORAC to confirm whether or not the ball would be stable in t'middle, or whether it would wobble about a lot. Me hears that gravity is the most chicken-sh1t of all forces, so one doubts whether the gravity of the sun or planets would be of much account. However, the moon might have a *lot* of influence, seeing as it's capable of pulling the surface of the oceans up a good few metres.

TW

Windy Militant
10th Apr 2006, 12:20
My mate Zog told me that's what happened to the fourth planet. They got beyond the arguing about what would happen stage and started digging a big hole. Unfortunately when they broke through the crust into the mantle, there was a very large pop and the asteroid belt was formed. :ouch:

Buster Hyman
10th Apr 2006, 13:09
It would never happen...whos going to drop the Asbestos ball eh?

Never thought of that did yers!

4Foxtrot
10th Apr 2006, 13:13
Never mind the billions of tonnes of very hot magma and the gravity that would tear one asunder, I ain't touching that asbestos ball. Health and safety y'see?


Ok, maybe if I had a yellow hi-viz jacket on...

PileUp Officer
10th Apr 2006, 13:23
Surely all the asbestos dust created by vehicle braking systems affects people badly.

Rise in motorcars and rise in cancers? Coincidence?

Tricky Woo
10th Apr 2006, 15:59
Yes, and why hasn't anyone linked the rise in asbestos-related employee claims with the rise in employee burns injuries? What's going on? Are these big multinational companies trying to avoid their asbestos legal responsibilities by setting their workers on fire? Did they think they could get away with this?

Hmm, is this a digression? I think it might be. But a tactical one, so that's ok.

One should never underestimate people's strong compulsion to digress, especially to digress blatantly.

One considers Winston Churchill's Gallipoli Campaign to be history's most impressive digression, if only in body count. However Uncle Adolf might have something to say about digressions, having needlessly poured about 25% of his military resources into a heap of digressions, from his North African campaigns, to Greece and, lawks a mercy, the Norwegian Campaigns.

Wherever Norway is.

Daft, that.

But those are strategic disgressions. Not much to admire about strategic digressions, other than their foolhardiness. One wonders if Napoleon's invasion of Russia was a digression, or whether it was part of his true strategy. If a digression, then he wins hands down.

TW

Loose rivets
10th Apr 2006, 16:36
Coo........just emerged from me slumbers to find someone has mentioned gravity.:8

Me hears that gravity is the most chicken-sh1t of all forces, so one doubts whether the gravity of the sun or planets would be of much account. TW

This is true, but it keeps yer porridge in the bowl, and the sea nicely wrapped round the globe...which it formed in the first place. Oh, and if you get enough of it, it'll light up the stars and overcome most other forces to the point of creating an alchemy that made all the atoms in you an me. Handy stuff, gravity...and it's not even really a force.

Now, as we are in orbit, would the Sun have any effect on such local ‘forces'. I'm not sure, but I think that if the Earth's axis was perpendicular to its orbit round the sun (which of course it isn't) then it would have no effect. As the angle got to anything like 20 degrees, so gravitational sheer would become a factor; the moon and tides being an example.

G-CPTN
10th Apr 2006, 16:42
Surely all the asbestos dust created by vehicle braking systems affects people badly.
A couple of decades ago (before asbestos was banned in brake linings) I asked (in my official capacity) what brake linings were made from. The Brake-Lining Rep said 'he couldn't tell me, as it was a trade secret'. I pushed my point, and he agreed that they were made predominantly from asbestos. I persevered and asked what became of these linings (made from asbestos). It was a slow and tedious conversation, but eventually he agreed that they ended-up as dust in the gutters of highways. When I suggested that you couldn't devise a more efficient distribution system even if you posted packets of the stuff through every letter box in Britain, he started to see what I was getting at!
Nowadays (and for a couple of decades now), brake linings have been made from ALTERNATIVES to asbestos, though nobody knows whether Kevlar or any of the artificial fillers are likely to cause malignancies.
http://www.madsci.org/posts/archives/aug2001/997280452.Eg.r.html

frostbite
10th Apr 2006, 17:27
Wouldn't it be handy if we could tap into all that heat for some of our energy generation?

ExSimGuy
10th Apr 2006, 17:50
Wouldn't the asbestos ball hit the turtle?
:uhoh:
Drapes old chap,

Would that be the Great A-Tuin, who swims through the universe, with 4 elephants on his back which in turn support the (disc) world?
http://www.ie.lspace.org/books/whos-who/images/atuin.jpg

:ok:

Bern Oulli
10th Apr 2006, 19:53
So how fast would the earth have to rotate for centrifugal force to cancel out gravity, i.e. throw you off into space? (measured at the equator of course.)

Edited to say GOSH, this is my 500th post. Well Yeeha!

tony draper
10th Apr 2006, 20:13
Oh dear me,tsk tsk tsk, Mr Bern,how could you?
:uhoh:
If one was you, one would edit one's edit one would,indeed one would.:E

handysnaks
10th Apr 2006, 20:46
No-one seems to ever want to make the first post in a new thread but once the replies start then everyone jumps in

I'm being Mr Picky here but surely only the thread starter can make the first post, the rest of us can only ever aspire to making the second post (A fine Bar and restaurant if ever there was one, with a very fine Goulash Soup)!

And is that two points for a double thread creep

chornedsnorkack
11th Apr 2006, 08:25
So how fast would the earth have to rotate for centrifugal force to cancel out gravity, i.e. throw you off into space? (measured at the equator of course.)



Again up to the fine details of mass distribution.

If the Earth is a completely hard ball, staying a sphere despite centrifugal forces, then naturally a turn in 85 minutes (just as the satellites orbit).

But the Earth is not hard and rigid, it will get elliptical. So, the period is somewhat longer... how long exactly would again depend on how the mass is distributed inside.

Tricky Woo
11th Apr 2006, 09:04
Oo-err, one has offended Mr Rivets by disparaging gravity.

But it's not me wot says gravity is weak, it's them physicists like that Mr ORAC. Facts are that the other forces are way stronger than gravity, and even the weak nuclear force has the muscle to beat up gravity on its way home from school.

Imagine what the strong nuclear force could do to it? Hah!

Hmm, the cosmologists have just invented a new force called 'dark energy'. And a new type of matter called 'dark matter'. Both concept are 'dark' because them haven't be detected directly, and many think they can't be. But the former simply must exist because the expansion of the universe is speeding up, and the latter likewise because galaxies are spinning so fast than their matter can't possibly stop them from flying apart into pieces.

Rowlocks, of course.

Newton built his theories around a fixed frame of reference for all. Not because he was unaware of the alternatives, but simply because it was prettier. Evidence gathered in the 19th century that a fixed frame of reference didn't fit after all. So Einstein redefined Newton's theories around unfixed frames of references, where every particle has its own frame of reference, hence relativity. Both smart boys, and we owe them both a bunch.

But what Einstein never had the stomach for was to answer this question: imagine a spiral galaxy sat in its own universe, and it's the only thing in there. Is it spinning? And if so, relative to what? And if not, why don't the stars clump together into one big fat black hole? Now imagine another universe with more than one galaxy, say two. They can now spin relative to each other, which fixes the collapsing stars problem. Phew! But why don't each of the galaxies squash against each other in the middle? Oh, they're orbiting each other? Ok, but relative to what? Buggah, we now have a collapsing galaxy problem. And the case for two galaxies leads to the same problem for our universe.

Yep, yer very own Tricky Woo is telling yer that we have a frame of reference problem, as bad as the one that did for Newton in the end. Accelerating expansion of the universe and underweight galaxies are just the start of it. Just you wait until the successor to the Hubble finally gets launched, then looks back to the so called dark ages of the universe just after the big bang and sees... oo-err, lots of mature galaxies. Then looks back to well before the start of the universe and sees, erm, yet more mature galaxies fading into the distance.

TW

PileUp Officer
11th Apr 2006, 09:37
I'm being Mr Picky here but surely only the thread starter can make the first post, the rest of us can only ever aspire to making the second post (A fine Bar and restaurant if ever there was one, with a very fine Goulash Soup)!
And is that two points for a double thread creep

My bad. I suppose I should have said first reply.

PileUp Officer
18th Apr 2006, 12:10
Alright I thought of this one whilst trying to get to sleep last night.

A car is travelling along at say, 200mph. On a perfectly flat road. Imagine a trench dug across the road perpendicular to the path of the car and with vertical sides.

What is the widest trench that the car could smoothly drive across without wiping out spectacularly?

Am I being stupid again?

G-CPTN
18th Apr 2006, 12:27
'Twould depend on the suspension (and weight distribution) of the vehicle. Front-end damping could delay the descent of the wheels (from the 'norm') and low-profile tyres would be worse than 'fat' tyres. Wheel diameter would also be influential. A heavier front-end weight would have stronger suspension springs (greater tendency to 'drop' the wheels). A dragster with no front suspension might float more readily . . .

Too difficult in other words :{

Polar moments of inertia and that . . .

sailing
18th Apr 2006, 12:45
Am I being stupid again?

No no no no no no no no no no no no on on no no no no YES!

ORAC
18th Apr 2006, 12:55
Ahem,

The earth cannot be taken in isolation but must be considered as part of the earth-moon system.

When a moon orbits around planet, or a planet orbits around a star, both of them are actually orbiting around their joint centre of mass, called the barycentre and around which both of them orbit. It is an important concept in the fields of astronomy, astrophysics, and the like.

In the case where one of the two objects is much larger and more massive than the other, such as with the earth-moon, the barycentre is located within the larger object. Rather than appearing to orbit the other body it will simply be seen to "wobble" slightly. In the case for the earth-moon, the barycenter is located on average 4,671 km from Earth's centre, but still within the earth´s radius of 6,378 km.

The ball will therefore finish pressed against the side of the hole at whichever point is nearest to the barycentre.

Pardon for the intrusion......

G-CPTN
18th Apr 2006, 12:57
Was that the LOAD of balls?

BlueWolf
18th Apr 2006, 13:15
Wouldn't it be handy if we could tap into all that heat for some of our energy generation?

Funnily enough, there are suggestions afoot that we should do just that, utilising, in the first instance, currently expended oil and gas wells.

The idea is to run a pipe down the said well, and back again, pour water down it, and collect the returning steam to run turbines and greehouses and suchlike.
Apparently, at the great depths to which many such old wells are drilled, temperatures may reach an as-yet-un-utilised 200 degrees C.

Wouldn't be the silliest idea I've heard.

Of course, some clever monkey would then suggest we dig straight into volcanoes, and of course there's possible retribution from the Core Dwellers to think about :uhoh:

BlueWolf
18th Apr 2006, 13:17
Is the car on a conveyor belt?

chornedsnorkack
18th Apr 2006, 13:26
Alright I thought of this one whilst trying to get to sleep last night.
A car is travelling along at say, 200mph. On a perfectly flat road. Imagine a trench dug across the road perpendicular to the path of the car and with vertical sides.
What is the widest trench that the car could smoothly drive across without wiping out spectacularly?
Am I being stupid again?
This has been discussed in another context... and it depends on the wheels. Sounds relevant to aviators.

If a plane is travelling at, say, 200 mph on a previously perfectly smooth runaway, like just before rotation on takeoff or just after touchdown on landing, and suddenly there is a hole in the runway ahead, what happens?

Once the support underneath vanishes (and the air is giving no support because the plane is not yet or no longer rotated for takeoff), the plane as a whole should accelerate down at 9,8 m/s/s. Thus, in 1 second, the plane falls 5 metres... in 0,1 seconds, the plane would fall just 5 cm.

What happens to tires that hit edge of runway 5 cm above the bottom of tire?

In 0,1 seconds, a plane at 200 mph should cover 9 metres. So, it might leap over pretty wide potholes.

But the wheel springs may cause problems... if the runway underneath vanishes, the gear might accelerate downwards at faster than 9,8 m/s/s by the force from springs!

So, how do aircraft deal with holes in runways?

ORAC
18th Apr 2006, 13:32
Well, if its a small hole the other wheels support it and the one over it goes and down, hopefully without damage. But if its a big hole.....

http://joatmoaf.typepad.com/i_love_jet_noise/images/nonotams1.jpg

http://joatmoaf.typepad.com/i_love_jet_noise/images/nonotams2_1.jpg

G-CPTN
18th Apr 2006, 13:34
The idea is to run a pipe down the said well, and back again, pour water down it, and collect the returning steam to run turbines and greehouses and suchlike.
Apparently, at the great depths to which many such old wells are drilled, temperatures may reach an as-yet-un-utilised 200 degrees C.
And you could run pipes up into the stratosphere and collect the cold . . .
DOES the energy expended in pumping the fluid down and up (or up and down) exceed the energy gained from the change in temperature?

G-CPTN
18th Apr 2006, 13:35
So, how do aircraft deal with holes in runways?
DEPTH (as well as width) is important.

ORAC
18th Apr 2006, 13:43
No, works well up or down. Down = Ocean Thermal Energy Conversion. (http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion) Up = Solar Chimney power plant. (http://www.solarmissiontechnologies.com/project-technology.htm)

G-CPTN
18th Apr 2006, 13:58
I know that leaving the hose-pipe uncoiled on the lawn (charged with water) will produce HOT water from the sun shining on it. Seems MUCH hotter than expected.

chornedsnorkack
18th Apr 2006, 14:10
And you could run pipes up into the stratosphere and collect the cold . . .
DOES the energy expended in pumping the fluid down and up (or up and down) exceed the energy gained from the change in temperature?

No, it should not.

Look at the Icelanders. They have plenty of hot springs. So, they tap the hot springs for swimming pools, central heating et cetera. I suppose the hot steam could be used for electricity, as well. It would be inefficient, but if the energy is cheap then it is better to use it wastefully than just let it go to waste. A pity is that you cannot really use electricity or geothermal energy to power cars or, worse, planes - you need something to burn inside them.

The Icelanders are not the only people to have hot springs.

And if you do not have hot springs naturally, you could bore them. I think that if you slow down the flow of water through a borehole, the energy spent on passing through a unit of water will decrease, but the amount of heat in that unit will not - so once the hole is there, you are sure to win.

Loose rivets
18th Apr 2006, 17:31
A car, which is perfectly rigid and having tires with no elasticity, AND, that happens to be travailing towards a hole in the road in a perfect vacuum, will be affected by gravity virtually instantaneously, and will therefore hit the opposite side-to a greater or lesser extent-depending on width / speed etc.

All of this doesn't matter, cos it will hit the opposite edge until the width is less than 1 Plank distance.

































The plank having been put across the ditch.:}

G-CPTN
18th Apr 2006, 17:37
Ani fule no that Planck's constant = 6.626068 Ũ 10-34 m2 kg / s

tony draper
18th Apr 2006, 17:42
Lots of frozen Methane Hydrate lying about the ocean floor why not tap that? or pump susperheated steam down bore holes into the coal measures and produce our own coal gas again, we got more coal that we can shake a stick at in this country,silly to rely on furriners for our supply,they's sneaky, tiz axiomatic, furriners = sneaky.
:rolleyes: