Science-based what-if questions

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Re: Science-based what-if questions

Postby Sableagle » Thu Oct 26, 2017 6:24 am UTC

Weakiepeedie:
The "kiloton (of TNT)" is a unit of energy equal to 4.184 terajoules.

The "megaton (of TNT)" is a unit of energy equal to 4.184 petajoules.

A gram of TNT releases 2673–6702 J (joules) upon explosion. The energy liberated by one gram of TNT was arbitrarily defined as a matter of convention to be 4184 J, which is exactly one kilocalorie, which is the approximate amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius at a pressure of one atmosphere.

The Little Boy atomic bomb dropped on Hiroshima on August 6, 1945, exploded with an energy of about 15 kilotons of TNT (63 TJ), and the Fat Man atomic bomb dropped on Nagasaki on August 9, 1945, exploded with an energy of about 20 kilotons of TNT (84 TJ). The modern nuclear weapons in the United States arsenal range in yield from 0.3 kt (1.3 TJ) to 1.2 Mt (5.0 PJ) equivalent, for the B83 strategic bomb.

The energy contained in one megaton of TNT (4.2 PJ) is enough to power the average American household for 103,000 years. The 30 Mt (130 PJ) estimated upper limit blast power of the Tunguska event could power the aforementioned home for just over 3,104,226 years. To put that in perspective, the energy of that blast could power the entire United States for 3.27 days.

The total energy of all explosives used in World War Two (including the Hiroshima and Nagasaki bombs) is estimated to have been three megatons of TNT.

Approximate total yield of the 1980 eruption of Mount St. Helens: 28 TWh, 24 MT TNT.


https://en.wikipedia.org/wiki/TNT_equivalent

Not listed: effect on Miami, Savannah, Norfolk, Baltimore, the Dominican Republic, the Turks and Caicos and the entire NE coast of South America of setting off a nuke deep inside the slip-fault on La Palma.
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Re: Science-based what-if questions

Postby Eebster the Great » Thu Oct 26, 2017 10:03 am UTC

Even 35 kPa overpressure is enough to demolish many fortified structures, and this is more than 70,000 times that, so the immediate area around the apple is going to have problems. I'm not sure whether there is not enough energy in the blast to compare to a nuke, but it sure looks like it.

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Re: Science-based what-if questions

Postby andykhang » Thu Oct 26, 2017 3:44 pm UTC

Then there's the sword...which must at least travel at relativistic speed to even achieve that...

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Re: Science-based what-if questions

Postby Sableagle » Thu Oct 26, 2017 4:25 pm UTC

500g sword attack portion at 500mm, from 200000000 m/s one way to 200000000 m/s the other in 0.000000001 s exerts how much torque on the hilt?

...

Quite.

...

I know velocity is funny stuff, and can cause weird things like copper cutting steel, but shouldn't putting a sword through an apple at insane speed cause two pieces of apple to separate at insane speeds? He wouldn't be slicing back and forth through a 6cm spherical space. He'd have to hit the diverging pieces of fruit. So, if two 50g pieces of apple set off in opposite directions at ... what? One tenth that slice speed? What's the edge angle on a sword?
https://www.google.co.uk/search?q=What' ... a+sword%3F
Apparently 40° is a popular total angle, so 20° each side. tan(20) = 0.36397, so 72794 km/s.
KE = 0.5 * 0.05 kg * (72794046 m/s)2 * 299792458 / ( 299792458 - 72794046) = 174956314633264 J

175 TJ in each half of the apple, more than Little Boy and Fat Man combined. 350 TJ in the two halves. Boom, baby.
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Re: Science-based what-if questions

Postby gmalivuk » Thu Oct 26, 2017 5:33 pm UTC

Eebster the Great wrote:Even 35 kPa overpressure is enough to demolish many fortified structures, and this is more than 70,000 times that, so the immediate area around the apple is going to have problems. I'm not sure whether there is not enough energy in the blast to compare to a nuke, but it sure looks like it.
Not even remotely close.

Sure 2.5 GPa is a lot, but that's only at the surface of an apple-sized region, which is about 4cm in radius. Ten meters away and you're already dropping below that 35 kPa level and by 25 you're only breaking windows.
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Re: Science-based what-if questions

Postby Eebster the Great » Thu Oct 26, 2017 7:52 pm UTC

gmalivuk wrote:
Eebster the Great wrote:Even 35 kPa overpressure is enough to demolish many fortified structures, and this is more than 70,000 times that, so the immediate area around the apple is going to have problems. I'm not sure whether there is not enough energy in the blast to compare to a nuke, but it sure looks like it.
Not even remotely close.

Sure 2.5 GPa is a lot, but that's only at the surface of an apple-sized region, which is about 4cm in radius. Ten meters away and you're already dropping below that 35 kPa level and by 25 you're only breaking windows.

Sounds about right, except the shockwave will rebound off the ground, so you should get some more distance than that. My 3 kK temperature estimate also is pretty low given it doesn't even reach the boiling point of carbon. If we go for something more like 10 kK, we get a pressure of 8.3 GPa. If we assume an inverse-square relationship, we get an overpressure of 35 kPa more like 20 m away, compared to about a kilometer for the bomb dropped on Hiroshima.

OK, so not particularly close, but still big compared to most conventional explosives.

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Re: Science-based what-if questions

Postby KittenKaboodle » Thu Oct 26, 2017 9:31 pm UTC

Sableagle wrote:but shouldn't putting a sword through an apple at insane speed cause two pieces of apple to separate at insane speeds?


You might check out What It #1.
I think others have mentioned, it would be far more than 2 pieces, I'd guess that a relativistic sword would get you a long way towards your goal with only one pass (a good thing since trying to reverse the sword and go back for another pass would have bad effects on whatever you are standing on)

But seriously a real sword can't do this, you'd have to use Magic (it's super effective, albeit fictional) and once you are using Magic you can make up pretty much anything you like. Sure the theoretical energy required to split apart molecules can be calculated, but the effects of the method used to do the splitting in this scenario would have to be largely imaginary.

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Re: Science-based what-if questions

Postby gmalivuk » Thu Oct 26, 2017 10:48 pm UTC

Eebster the Great wrote:
gmalivuk wrote:
Eebster the Great wrote:Even 35 kPa overpressure is enough to demolish many fortified structures, and this is more than 70,000 times that, so the immediate area around the apple is going to have problems. I'm not sure whether there is not enough energy in the blast to compare to a nuke, but it sure looks like it.
Not even remotely close.

Sure 2.5 GPa is a lot, but that's only at the surface of an apple-sized region, which is about 4cm in radius. Ten meters away and you're already dropping below that 35 kPa level and by 25 you're only breaking windows.

Sounds about right, except the shockwave will rebound off the ground, so you should get some more distance than that. My 3 kK temperature estimate also is pretty low given it doesn't even reach the boiling point of carbon. If we go for something more like 10 kK, we get a pressure of 8.3 GPa. If we assume an inverse-square relationship, we get an overpressure of 35 kPa more like 20 m away, compared to about a kilometer for the bomb dropped on Hiroshima.

OK, so not particularly close, but still big compared to most conventional explosives.
Oh for sure it's not a small bang by any means, it just doesn't compare to a nuke.
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Re: Science-based what-if questions

Postby Eebster the Great » Fri Oct 27, 2017 12:31 am UTC

Even small nukes can really impress me with their power. They're even more explosive than apples!

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Re: Science-based what-if questions

Postby Zamfir » Fri Oct 27, 2017 8:14 am UTC

Given that we're liberating chemical energy, then this should be fairly similar to the detonation of an apple-sized explosive charge, right?

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Re: Science-based what-if questions

Postby Eebster the Great » Fri Oct 27, 2017 9:14 am UTC

Zamfir wrote:Given that we're liberating chemical energy, then this should be fairly similar to the detonation of an apple-sized explosive charge, right?

You're not liberating chemical energy. You are breaking every bond. You are adding a huge amount of chemical energy. The energy for all of this is coming from the sword, not from chemistry.

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Re: Science-based what-if questions

Postby andykhang » Fri Oct 27, 2017 12:13 pm UTC

So from what I gathered, the slice itself would do (astronomically) more damage than the apple itself. I would imagine that much energy compacted into a blade would generate quite a vacumn blade before instantly evaporated from blade to handle.

Edit:...Then again, I not sure there would be air left to even make that after this...Maybe electron wave?

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Re: Science-based what-if questions

Postby gmalivuk » Fri Oct 27, 2017 1:28 pm UTC

What do you mean "vacuum blade"?
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Re: Science-based what-if questions

Postby p1t1o » Fri Oct 27, 2017 3:28 pm UTC

This discussion is....hard. Too much fiction mixed in with science.

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Re: Science-based what-if questions

Postby gmalivuk » Fri Oct 27, 2017 3:44 pm UTC

Yeah, it would probably be easier to follow (and more scientific) if the question had just been, "What would happen if we somehow broke all the molecular bonds in an apple?" instead of bringing a magical sword into the mix.

(Sure, the mechanism by which the bonds are broken is still handwaved, but at least that doesn't bring in an additional complication the way positing a magical sword does.)
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Re: Science-based what-if questions

Postby andykhang » Sat Oct 28, 2017 4:29 am UTC

Well, thing kinda get to this point, as I wondered...So what would happen if you swing a normal sword at that speed anyway?

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Re: Science-based what-if questions

Postby Soupspoon » Sat Oct 28, 2017 7:01 am UTC

Visually, something like a light-sabre? But only momentarily, then like a light-whip as the arc extends, then "a major incident", most likely.

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Re: Science-based what-if questions

Postby gmalivuk » Sat Oct 28, 2017 3:24 pm UTC

andykhang wrote:Well, thing kinda get to this point, as I wondered...So what would happen if you swing a normal sword at that speed anyway?
It would quickly break apart because no part of it is strong enough to handle those forces.
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Re: Science-based what-if questions

Postby Sableagle » Sat Oct 28, 2017 5:00 pm UTC

https://www.azom.com/article.aspx?ArticleID=6575

Density 7.85 g/cm3 0.284 lb/in³

Properties Metric Imperial
Tensile strength, ultimate 635 MPa 92100 psi
Tensile strength, yield 490 MPa 71100 psi
Modulus of elasticity 0.27-0.30 0.27-0.30
Bulk modulus (typical for steel) 140 GPa 20300 ksi
Elongation at break (in 50 mm) 10% 10%


Image

I'm sorry. Really, I am sorry, but after so many pages of irrelevant results, I went for the first image showing dimensions of a sword blade I found, even if it is a picture of a table using mixed imperial and metric measures. I'm sick of diagrams of stances and labelled images telling me which end is the point.

Right, so, anyway, the 16" from PoP to 1" from point have width from 0.6" to 0.25" and thickness from 4.5 mm to 2.2 mm, which assuming a rhombus cross-section is 0.5 * ((2.2 + 4.5) / 2) * 25.4 * ((0.6 + 0.25) / 2) = 18 mm2 average cross-section ... I hope. 10.795 mm mean width, 3.35 mm mean thickness, 36.16 mm2 rectangular, 18.08 mm2 rhombus, yes? That * 16" * 25.4 mm/inch = 7348 mm3 = 7.348 cm3. That * 7.85 g/cm3 = 57.6847 g of steel out there.

A pivot at the elbow will put the guard at about 45 cm. That makes the mid-point of that length of steel 29.5" + 45 cm = 119.93 cm from the pivot. Given a linear velocity of 200000000 m/s, a = v2/r = 40000000000000000/1.1993 and
F = ma = 0.001 * 57.6847 * 40000000000000000 / 1.1993 = 1923946413407821 N.

Cross-section at guard is 1" * 4.9 mm and I'll assume it's closer to rectangular there, being 20 mm * 4.9 mm with a 2.7 mm triangular wedge each side, total 20 * 4.9 + (2 * (2.7 * 4.9) / 2) = 22.7 * 4.9 = 111.23 mm2 = 0.00011123 m2.

Tension in the blade at the guard from accelerating those 16" between PoP and 1" from point at that rate for that swing = 1923946413407821 N / 0.00011123 m2 = 1.7297 * 1019 Pascals.

Tensile strength was something * 108 Pascals.

She cannae teck it, skippah!

You'd have to slow down to maybe 200 m/s, the speed of a .45 ACP bullet ... erm ... more than 600 yards down-range.
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Re: Science-based what-if questions

Postby gmalivuk » Sat Oct 28, 2017 11:56 pm UTC

Sableagle wrote:1923946413407821 N.
You probably don't need quite so many significant digits when the end result is eleven orders of magnitude greater than what you're comparing it to.
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Re: Science-based what-if questions

Postby Sableagle » Sun Oct 29, 2017 12:48 am UTC

"Try swinging a metre of over-cooked spaghetti" would have been adequate, really.
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Re: Science-based what-if questions

Postby andykhang » Sun Oct 29, 2017 7:28 am UTC

If the same over-cooked spaghetti is also made out of anti-matter, more like.

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Re: Science-based what-if questions

Postby Soupspoon » Sun Oct 29, 2017 1:42 pm UTC

andykhang wrote:If the same over-cooked spaghetti is also made out of anti-matter, more like.

Would that be considered as antipasto?

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Re: Science-based what-if questions

Postby Sableagle » Sun Oct 29, 2017 2:32 pm UTC

Antifuturo, too.
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Re: Science-based what-if questions

Postby p1t1o » Mon Oct 30, 2017 1:58 pm UTC

gmalivuk wrote:Yeah, it would probably be easier to follow (and more scientific) if the question had just been, "What would happen if we somehow broke all the molecular bonds in an apple?" instead of bringing a magical sword into the mix.

(Sure, the mechanism by which the bonds are broken is still handwaved, but at least that doesn't bring in an additional complication the way positing a magical sword does.)


Thing is, breaking bonds isnt even that special. Even just normally cutting an apple in half breaks uncountable bonds. Even bonds in the knife.
And just eating the apple breaks an even larger proportion of the bonds.

A sword going 0.99c? Yeah thats special.

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Just because its slightly alongside the subject - anyone ever look at a razor blade under an electron microscope?
I have and they are ludicrously blunt. I compared it to a shard of broken glass and it was like comparing the edge of a piece of paper (the glass) with a marshmallow (the razor). I actually could keep zooming to the limit of the scope and could not get resolution on the edge of the glass. Its common knowledge that a piece of broken glass can give an atomic-scale edge but its another thing to see it, and to compare it to something we normally regard as "very sharp".

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Re: Science-based what-if questions

Postby HES » Mon Oct 30, 2017 2:08 pm UTC

Should a razor blade be "very sharp"? I want it to be sharp enough to easily cut hair, but blunt enough that I don't constantly cut myself.
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Re: Science-based what-if questions

Postby p1t1o » Mon Oct 30, 2017 3:05 pm UTC

HES wrote:Should a razor blade be "very sharp"? I want it to be sharp enough to easily cut hair, but blunt enough that I don't constantly cut myself.


Well given that hair is tougher than skin, thats a tall ask.

Yes, I think I will go out on a limb and say razor blades are supposed to be, and practically speaking generally are, "very sharp" :)

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Re: Science-based what-if questions

Postby Sableagle » Mon Oct 30, 2017 5:04 pm UTC

Having given the matter further thought, I realise the inability of the sword blade to withstand the tension of swinging its own mass at that speed is irrelevant, because for that to happen we'd have to accelerate it up to that speed.

I *was* going to look up the shear strength of the blade and see how many orders of magnitude beyond it you'd be pushing the hilt to make the blade go from standstill to swing speed in so little time. Even that, though, may not be where the failure occurs.

I think if you made a vibranium golem and had it swing the sword, with all the magical acceleration necessary, the sword hilt would come out through the spaces between the golem's fingers like a stick of butter hitting the undercarriage of an oncoming aircraft.
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Re: Science-based what-if questions

Postby Eebster the Great » Mon Oct 30, 2017 5:25 pm UTC

Razor blades are basically supposed to be as sharp as reasonably possible. Obviously other considerations like strength and cost make materials like diamond, obsidian, and titanium diboride unacceptable substitutes for steel, but there is no reason it couldn't be chromium plated or something if you really need a sharp edge. But I think at the end of the day, there is just no need for anything harder than stainless steel.

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Re: Science-based what-if questions

Postby p1t1o » Tue Oct 31, 2017 12:01 pm UTC

FunFact - apparently obsidian blades are sometimes still used in eye surgery due to their extreme sharpness.

FunFact #2 - In the same course I also used transmission electron microscopy - this is the one where you look at very thin slices of a subject. To make the slices we used a diamond knife. This was a small block of copper abut an inch long, with a blade about 4mm wide set in it. It cost around $10,000. I couldnt tell you how sharp it was because I mostly just cut resin, and I wasnt going to be the guy that broke a 10k piece of kit! (there were much cheaper things to **** about with ;)

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Re: Science-based what-if questions

Postby Eebster the Great » Wed Nov 01, 2017 8:19 am UTC

That's not the first time I've heard people talk about the cost of a blade or bit or whatever, and I never understood it. The raw material cost of that quantity of diamond and copper is negligible compared to the cost of the tool. What is actually so expensive?

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Re: Science-based what-if questions

Postby p1t1o » Wed Nov 01, 2017 2:11 pm UTC

Eebster the Great wrote:That's not the first time I've heard people talk about the cost of a blade or bit or whatever, and I never understood it. The raw material cost of that quantity of diamond and copper is negligible compared to the cost of the tool. What is actually so expensive?


I think its to do with the quality of the crystal and precision of manufacture, it needs to be very low on flaws, and the blade itself must be very carefully ground.
The edge will be under extreme pressure and it is possible to damage the blade if you are reckless with the ultra-micro-tome (the machine into which the blade fits, for planing micrometre-thick sample slices). The edge must be of very high quality (for example, far higher quality than the aforementioned razor blade, by orders of magnitude) because you are looking at the slices under 100,000+ magnification, so scratches and imperfections are a big deal, it could destroy the sample.
Also, they dont sell millions of them, small batch size increases cost.

And of course, the usual commercial markup.

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Re: Science-based what-if questions

Postby Eebster the Great » Wed Nov 01, 2017 10:42 pm UTC

Well, flawless diamonds aren't actually that expensive. (I mean, they are very expensive, but for the size and optical quality of diamonds used for a blade, they are not expensive compared to a $10,000 price tag.) But I can imagine how precision-grinding a single crystal diamond could be extremely labor-intensive. And yeah, small sample size obviously makes a big difference.

On that last note, it took me a long time to understand how niche technical software could be so extremely expensive until I realized how few people bought each program compared to how long it took to write.

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Re: Science-based what-if questions

Postby Liri » Wed Nov 01, 2017 11:10 pm UTC

Eebster the Great wrote:On that last note, it took me a long time to understand how niche technical software could be so extremely expensive until I realized how few people bought each program compared to how long it took to write.

Some of the stuff my lab does is very niche and the software to run the (also very expensive equipment) is in the tens of thousands of dollars. When I've talked and e-mailed with their tech support staff, it's clear they don't even understand pretty important parts of it. We've had to ignore them to get very basic things to work.

Based on the time it takes to get new parts delivered, they probably don't get things made until they have an order for them.
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Re: Science-based what-if questions

Postby Eebster the Great » Thu Nov 02, 2017 12:56 am UTC

Liri wrote:
Eebster the Great wrote:On that last note, it took me a long time to understand how niche technical software could be so extremely expensive until I realized how few people bought each program compared to how long it took to write.

Some of the stuff my lab does is very niche and the software to run the (also very expensive equipment) is in the tens of thousands of dollars. When I've talked and e-mailed with their tech support staff, it's clear they don't even understand pretty important parts of it. We've had to ignore them to get very basic things to work.

I've never used anything really niche, but I interned for about a year modeling insulin analogues, and the software I used for molecular dynamics and quantum chemistry could be fairly expensive. Most were pretty cheap for schools and researchers, but Gaussian cost $5,000 ($6,000 with source code), and it apparently charges commercial customers in the U.S. $35,000, and in India, $48,700, with an additional fee for each additional machine type. That's pretty damn expensive.

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Re: Science-based what-if questions

Postby Liri » Thu Nov 02, 2017 4:33 am UTC

I was looking at some 3D modelling software for medical CT scans and it was well over $100,000.
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Re: Science-based what-if questions

Postby Sableagle » Thu Nov 02, 2017 5:18 pm UTC

Liri wrote:Based on the time it takes to get new parts delivered, they probably don't get things made until they have an order for them.
At least the delivery mechanism didn't look like this:

Image

On the plus side, when they're using one of them, they do *not* do this to you:

Image

On the other hand, a FedEx van breaking down on the road doesn't turn its cargo into fireworks.
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Penetrate Earth

Postby andykhang » Mon Nov 06, 2017 4:37 am UTC

So, I have asked for a Matter-Antimatter Anti-Structure Sniper Rifle earlier in this thread. Now, I wanted to test this, and to do that, I need a target, a huuuuge target. So, I decided to aim it down, lock and loaded, and it's time to penetrate Earth. Supposed I aimed it straight down, and used the same indestructable bullet last time, what speed do I need to achieve to do that?

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Re: Science-based what-if questions

Postby gmalivuk » Mon Nov 06, 2017 2:38 pm UTC

The problem is, the faster the bullet moves, the faster it has to push stuff out of its way, so an approximation that considers just the transfer of momentum doesn't depend on velocity at all.
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p1t1o
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Re: Penetrate Earth

Postby p1t1o » Mon Nov 06, 2017 2:43 pm UTC

andykhang wrote:So, I have asked for a Matter-Antimatter Anti-Structure Sniper Rifle earlier in this thread. Now, I wanted to test this, and to do that, I need a target, a huuuuge target. So, I decided to aim it down, lock and loaded, and it's time to penetrate Earth. Supposed I aimed it straight down, and used the same indestructable bullet last time, what speed do I need to achieve to do that?


Lets assume your aim is to shoot a bullet through the Earth.

I dont think there is any speed that would not result in an explosion and a crater, rather than a "penetration".
You'd have to blow up the whole Earth to say you had pierced it all the way through.
The faster an impact, the more spherical - and less linear - the zone of destruction. Even with an indestrukt-i-bulletTM.
At a certain point, an ultra-fast impact just starts resembling a larger and larger nuke.
And you'd need a very large nuke indeed to "penetrate" the Earth, and I doubt there'd be much left.

Compare this against what you know about asteroid impactors - compared to the Earth, the explosions are impressive, but the craters they leave are very wide and very shallow.



You need a new bullet. One with particular properties, in this case, extreme density.
Enough density to shift the problem from one of kinetic penetration to one of material properties. So that it is no longer a question of simply kinetic energy but gravitational potential.
You need a bullet made of neutronium, or better yet, since neutronium really wants to explode unless there is a lot of it, a bullet made of a small black hole.

A Quantum Singul-bullet-yTM.

I havent done the exhaustive math, but this could probably just be dropped and it would go most of the way through the Earth.
Fire it at the ground at just over escape velocity, and it should exit the other side of the Earth going slightly slower, fulfilling your "through the Earth" requirement. There would be a colossal explosion for sure but I feel like the Earth would remain [largely] intact - since only a fraction of the hole's kinetic energy would be transferred to the Earth at all.


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