Science-based what-if questions

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madaco
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Re: Planet's spin

Postby madaco » Thu Mar 16, 2017 8:56 am UTC

in 4d space I think there can be 2 axes of rotation which are at independant speeds.

Idk how many dimensions you need for 3 axis. I'm guessing 6 spatial dimensions?
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Re: Planet's spin

Postby ElWanderer » Thu Mar 16, 2017 9:04 am UTC

LaserGuy wrote:Mercury, for example, is tidally locked to the Sun, so it has a permanent light and dark side.

Being pedantic, Mercury has a 3:2 resonance with the sun so it doesn't have permanent day- or night-side. It rotates three times every two orbits (note: I should double check that's not the other way around). This kind of resonance is an alternative 'end state's to being tidally locked.
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Re: Planet's spin

Postby Soupspoon » Thu Mar 16, 2017 9:09 am UTC

Mercury is actually 3:2 'locked', in resonance. It spins three times (WRT star background) for every two solar orbits (ditto), making the day (WRT Sol) half the period of the year (three rotations minus the two orbits taken during that time, or one subjective day per two subjective years). Which is confusing to imagine. But Venus is odder, spinning slower than it orbits, thus Sol would appear to be retrograde to the star background, if you could see both - I think. Confusing.

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Uranus is tilted sideways, slightly more than 90 degrees (crossing its orbital plane), so could be considered to be effectively counter-spinning at just less than 90 degrees. Odd enough, either way, from our perspective. Subjectively, it would probably appear that in a Uranocentric model of the universe, without the star backround bisible through the cloudsSol would orbit)

LaserGuy talks of spin being transfered away. You could also transfer (counter-) spin onto the planet. Probably a massive bombardment (one very big object, or loads of little ones, aimed overwhelmingly to the appraching side, forcing it back). Either way, you probably don't have the planet you started with, as nudging it to a standstill (solar-wise, never mind sidereal) is going to cause other changes.

Probably the 'safest' way is a very contrived engineering project like an equatorial maglev track flinging huge masses around a vacuum tunnel at impossible speeds, to exploit conservation of momentum, before sending them up an exit tube throwing them into space before the momentum is 'reabsorbed'. You'd have to really want to do that, though, and probably quite persistent at it.


(Prediction: this gets merged into the general Science Questions thread, like other threads you created... But I'm not making that decision, just guessing.)

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Re: Planet's spin

Postby p1t1o » Thu Mar 16, 2017 9:16 am UTC

There can be more than one axis of rotation, it just takes an energy input to keep it going - left without external influence, the second axis would gradually disappear, and I presume the angular momentum would transfer to the major axis.

The Earth, for example, "precesses" around an axis several degrees off the main axis. Howver, this axis rotates very slowly, once in 26,000 years. The energy input comes from the gravitational influence of the sun and moon on the Earths slightly irregular "oblate spheroid" shape.

Stopping the rotation would be problematic. The kinetic energy stored in a rotating ball of iron the size of the Earth is colossal - 2.14e29J

For comparison, that represents the total energy out put by the sun over about 10minutes.

Or if you prefer units of Tsar Bombas (50 megaton nukes), it represents around 1000 trillion of those.

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Re: Planet's spin

Postby andykhang » Thu Mar 16, 2017 11:10 am UTC

Yeah, I was talking about that: take the earth current axis, spin it with the force perpendicular to the original spin, then take that new axis and doing the same thing. What would the view be like?

And what are you saying earlier suddenly make me thought of a vector weapon... but that landed in SF territory.

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Re: Planet's spin

Postby p1t1o » Thu Mar 16, 2017 11:43 am UTC

andykhang wrote:Yeah, I was talking about that: take the earth current axis, spin it with the force perpendicular to the original spin, then take that new axis and doing the same thing. What would the view be like?

And what are you saying earlier suddenly make me thought of a vector weapon... but that landed in SF territory.


Doing this would create a torque that would create a new spin axis somewhere...I cant quite remember how to figure out where but it wouldn't be where you were trying to put it. Reading about how helicopters fly is a good primer for this sort of thing.

You dont end up with two spin axes, you just moving the first one. In order to get it to truly rotate about two axes would require continual (and extreme) energy input.

In any case, the amount of energy you would need to put into the Earth to do this, and the forces involved in changing the direction in which all of that mass is moving is within 3-4 orders of magnitude of the gravitational binding energy of the Earth.

So whilst the forces and energies involved here are not enough to convert the Earth into an expanding cloud of rubble, you get the idea: the Earth may not survive in its current form.

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Re: Planet's spin

Postby andykhang » Thu Mar 16, 2017 12:38 pm UTC

Ohhhh... but in that short while, if you stand on it surface, what do you see in the sky (aside from debris and stuff)

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Re: Planet's spin

Postby p1t1o » Thu Mar 16, 2017 12:46 pm UTC

andykhang wrote:Ohhhh... but in that short while, if you stand on it surface, what do you see in the sky (aside from debris and stuff)


Well when I look up today I see nothing, because the angular motion is too slow at night to see the stars move across my field of vision, and at day, well it all just blue sky.
I presume it would be the same if you were to start manipulating axes, until you got distracted by the mega-earthquakes, possible super-hurricanes, tidal waves etc.
Gravity may appear to be acting in a slightly diagonal direction as the acceleration affects you, the severity of the change depending on the severity of the motion.

Of course if you are using stupid high amounts of energy and start whipping the Earth about like a top, in which case you'd see what you'd expect (whilst you were still around to observe) - the stars (lets assume its night) making strange motions about the sky until you died in any number of ways.
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Re: Planet's spin

Postby Soupspoon » Thu Mar 16, 2017 3:29 pm UTC

p1t1o wrote:Well when I look up today I see nothing, because the angular motion is too slow at night to see the stars move across my field of vision

Stand for five minutes and things definitely move, if you stare at the night sky. (I think 8 minutes is enough for the trail end of Orion's Belt to get to where the, end of it was...) The Moon perceptively moves, and if you haven't watched with interest a long shadow move across the ground during an idle daytime moment (or seen the sun rise or set, with all due care an attention to your sight, but the proximity of the horizon may be considered cheating) then you've never really relaxed..!

Not saying that you could tell if it was going slightly faster or slower (ignoring the other effects, if the transition was happening whilst you were looking), but it'd probably be noticed by a more habitual skywatcher...

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Re: Planet's spin

Postby p1t1o » Thu Mar 16, 2017 4:11 pm UTC

Soupspoon wrote:
p1t1o wrote:Well when I look up today I see nothing, because the angular motion is too slow at night to see the stars move across my field of vision

Stand for five minutes and things definitely move, if you stare at the night sky. (I think 8 minutes is enough for the trail end of Orion's Belt to get to where the, end of it was...) The Moon perceptively moves, and if you haven't watched with interest a long shadow move across the ground during an idle daytime moment (or seen the sun rise or set, with all due care an attention to your sight, but the proximity of the horizon may be considered cheating) then you've never really relaxed..!

Not saying that you could tell if it was going slightly faster or slower (ignoring the other effects, if the transition was happening whilst you were looking), but it'd probably be noticed by a more habitual skywatcher...


Cant say I've ever tried for that long, but that definitely sounds faster than I thought! I'll have to try it sometime 8-)
I've seen shadows move, but of course that can be magnified by an arbitrary factor depending on geometry.

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Re: Planet's spin

Postby gmalivuk » Thu Mar 16, 2017 4:50 pm UTC

Earth rotates at about 1 degree every 4 minutes, which means the width of the sun or moon every 2 minutes or so. But unless you're watching the horizon, this isn't generally perceptible.
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Re: Planet's spin

Postby cyanyoshi » Fri Mar 17, 2017 1:36 am UTC

madaco wrote:in 4d space I think there can be 2 axes of rotation which are at independant speeds.

Idk how many dimensions you need for 3 axis. I'm guessing 6 spatial dimensions?


The idea of an axis of rotation only works in 3D space. That's because if things are moving round in a circle in 2 of the dimensions, that leaves just 1 dimension that isn't rotating. In 4+ dimensional space, it's better to think of rotations as happening in several independent 2D subspaces.

I'm not sure if this is the original intent, but things in the real world do rotate in funny 3-dimensional ways described as rates of change of the Euler angles. The Earth already experiences rotation, procession, and nutation.

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Re: Planet's spin

Postby madaco » Fri Mar 17, 2017 4:10 am UTC

cyanyoshi wrote:
madaco wrote:in 4d space I think there can be 2 axes of rotation which are at independant speeds.

Idk how many dimensions you need for 3 axis. I'm guessing 6 spatial dimensions?


The idea of an axis of rotation only works in 3D space. That's because if things are moving round in a circle in 2 of the dimensions, that leaves just 1 dimension that isn't rotating. In 4+ dimensional space, it's better to think of rotations as happening in several independent 2D subspaces.

I'm not sure if this is the original intent, but things in the real world do rotate in funny 3-dimensional ways described as rates of change of the Euler angles. The Earth already experiences rotation, procession, and nutation.


Whoops, I guess its not quire an axis, yeah.

I think I've heard the term "bivectors" wrt rotations in multiple dimensions?
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Re: Science-based what-if questions

Postby Eebster the Great » Fri Mar 17, 2017 1:45 pm UTC

Your description of something heavy hitting a stick and driving it into the ground without breaking it sounds almost exactly like a description of an actual pile driver.

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Re: Planet's spin

Postby cyanyoshi » Fri Mar 17, 2017 9:47 pm UTC

madaco wrote:
cyanyoshi wrote:
madaco wrote:in 4d space I think there can be 2 axes of rotation which are at independant speeds.

Idk how many dimensions you need for 3 axis. I'm guessing 6 spatial dimensions?


The idea of an axis of rotation only works in 3D space. That's because if things are moving round in a circle in 2 of the dimensions, that leaves just 1 dimension that isn't rotating. In 4+ dimensional space, it's better to think of rotations as happening in several independent 2D subspaces.

I'm not sure if this is the original intent, but things in the real world do rotate in funny 3-dimensional ways described as rates of change of the Euler angles. The Earth already experiences rotation, procession, and nutation.


Whoops, I guess its not quire an axis, yeah.

I think I've heard the term "bivectors" wrt rotations in multiple dimensions?


Yes. Bivectors are a good way to describe planes of rotation, which was what I was referring to.

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Re: Planet's spin

Postby Sheikh al-Majaneen » Fri Mar 17, 2017 10:08 pm UTC

p1t1o wrote:There can be more than one axis of rotation, it just takes an energy input to keep it going - left without external influence, the second axis would gradually disappear, and I presume the angular momentum would transfer to the major axis.


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In the case of bomb

Postby andykhang » Sat Mar 18, 2017 6:14 pm UTC

Would you rather releashing as much energy as possible, or for that energy to invite and generate more energy, and thus more destruction? (Obviously, both as the same time would be great)

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Re: In the case of bomb

Postby Soupspoon » Sat Mar 18, 2017 8:52 pm UTC

Is the question "instantaneous explosion" vs "slower build up of force that uses its time to tap into other (non-bomb) reserves of energy"?

Like... Erm a device leaning against a wall that damages the wall next to the device a little, but mostly creating a bang and a plume of smoke in the air, vs the same energy going directly into drilling/burning through the wall base, until it causes a collapse of the whole structure... Maybe..

(This is one of those many little questions things, I suspect. Once you clarify it...)

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Re: In the case of bomb

Postby gmalivuk » Sun Mar 19, 2017 4:28 am UTC

Soupspoon wrote:(This is one of those many little questions things, I suspect. Once you clarify it...)

Indeed.

You could also start a (as in, one) thread in the Fictional Science forum, if most of these are for story ideas.
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Re: In the case of bomb

Postby andykhang » Sun Mar 19, 2017 4:42 am UTC

Soupspoon wrote:Is the question "instantaneous explosion" vs "slower build up of force that uses its time to tap into other (non-bomb) reserves of energy"?

Like... Erm a device leaning against a wall that damages the wall next to the device a little, but mostly creating a bang and a plume of smoke in the air, vs the same energy going directly into drilling/burning through the wall base, until it causes a collapse of the whole structure... Maybe..

(This is one of those many little questions things, I suspect. Once you clarify it...)


That case, basically. Also a bit of "big boom vs chain reaction" too.

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Re: Planet's spin

Postby Sableagle » Sun Mar 19, 2017 10:21 am UTC

andykhang wrote:Ohhhh... but in that short while, if you stand on it surface, what do you see in the sky (aside from debris and stuff)


A very, very bright light.

2.14e29J?

Earth Impact Effects Program


Distance from Impact: 5000.00 km ( = 3110.00 miles )
Projectile diameter: 500.00 km ( = 311.00 miles )
Projectile Density: 8000 kg/m3
Impact Velocity: 20.00 km per second ( = 12.40 miles per second )
Impact Angle: 1 degrees
Target Density: 2750 kg/m3
Target Type: Crystalline Rock


Energy before atmospheric entry: 1.05 x 1029 Joules = 2.50 x 1013 MegaTons TNT
The average interval between impacts of this size is longer than the Earth's age.
Such impacts could only occur during the accumulation of the Earth, between 4.5 and 4 billion years ago.


The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 13.6 minutes.
The impact does not shift the Earth's orbit noticeably.




Time for maximum radiation: 7.86 minutes after impact

Your position is inside the fireball.
The fireball appears 344 times larger than the sun
Thermal Exposure: 1.50 x 1012 Joules/m2
Duration of Irradiation: 34 hours
Radiant flux (relative to the sun): 12200
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Re: Science-based what-if questions

Postby Sableagle » Wed Mar 22, 2017 4:39 pm UTC

Today's thought (yeah, sometimes they happen to me): if two people with matching blood-types are linked up, effectively creating siamese twins that share a kidney, would that work like or better than a dialysis machine, and for how long?

Follow-up thought: could an identical twin's immune system be used as a weapon against cancer?
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Re: Science-based what-if questions

Postby Angua » Wed Mar 22, 2017 4:48 pm UTC

That would effectively be the same as a transplant. Ignoring the problems getting the two circulatory systems to function together you'd run into tissue rejection. It's also hard to get blood types that match up exactly - you've got all the random ones like Kell and Duffy that start being a problem with regular transfusions as well.
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Re: Science-based what-if questions

Postby Eebster the Great » Thu Mar 23, 2017 6:02 am UTC

Angua wrote:That would effectively be the same as a transplant. Ignoring the problems getting the two circulatory systems to function together you'd run into tissue rejection. It's also hard to get blood types that match up exactly - you've got all the random ones like Kell and Duffy that start being a problem with regular transfusions as well.

Do these problems apply to homozygotic twins? I would think that genetically-coded factors would be the primary cause of tissue rejection, but I know hardly anything about it.

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Relativistic ballistic problem and factor

Postby andykhang » Thu Mar 23, 2017 6:18 am UTC

What would be the factor you needed in order to shoot a relativistic weaponry (like, said, a bullet that travel at 0.5c)? One of the thing I thought of is "Over the Horizon" (which already become problematic with regular gun), and how, for some targer, you need to literally shoot through the earth in order to hit farther out. Other would be nuclear explosion cause by drag and how it would hit the moon behind.

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Re: Science-based what-if questions

Postby Angua » Thu Mar 23, 2017 8:44 am UTC

No, but then you still have the problems matching up the circulations.

Anyway, a kidney transplant is the way you should go. Dialysis is not a good permanent solution, and we're describing a scenario where you have someone who's a match.

Also, for the identical twin cancer thing - I don't think so. The priming in the thymus to teach T cells what self tissue is like would pretty much be the same in both individuals, and it is often factors given off by the cancer itself that stops it from being recognised as non-self.
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Re: Relativistic ballistic problem and factor

Postby gmalivuk » Thu Mar 23, 2017 12:20 pm UTC

andykhang wrote:What would be the factor you needed in order to shoot a relativistic weaponry (like, said, a bullet that travel at 0.5c)? One of the thing I thought of is "Over the Horizon" (which already become problematic with regular gun), and how, for some targer, you need to literally shoot through the earth in order to hit farther out. Other would be nuclear explosion cause by drag and how it would hit the moon behind.

Most of your weapon ideas simply don't make sense for planet-based combat. If you want to hit a planetary target faster than it can react, shoot your relativistic projectiles from space.
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Re: Relativistic ballistic problem and factor

Postby andykhang » Thu Mar 23, 2017 12:50 pm UTC

gmalivuk wrote:
andykhang wrote:What would be the factor you needed in order to shoot a relativistic weaponry (like, said, a bullet that travel at 0.5c)? One of the thing I thought of is "Over the Horizon" (which already become problematic with regular gun), and how, for some targer, you need to literally shoot through the earth in order to hit farther out. Other would be nuclear explosion cause by drag and how it would hit the moon behind.

Most of your weapon ideas simply don't make sense for planet-based combat. If you want to hit a planetary target faster than it can react, shoot your relativistic projectiles from space.


I don't said it's a planet-based combat though, but just regular ground combat (because no kill like overkill,amiright?). If it were a planet-based combat, you don't need to worry about defense factor, since it's the end for most civilization aside from type 2 and up, offense and stealth action must be considered though, like to detect before it begin it R-trajectory, or go past that countermeasure.

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Re: Science-based what-if questions

Postby morriswalters » Thu Mar 23, 2017 1:55 pm UTC

It's been done in fiction. In the Forever War a missile moving at relativistic speeds is used to destroy an enemy base on a planet. Sets off planet quakes. Read more SF. It works well in that context since a planets motion is fairly predictable. Otherwise I don't see much utility as a fictional device, since you have to know where your target will be at the moment of intercept, before you fire.

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Re: Science-based what-if questions

Postby andykhang » Thu Mar 23, 2017 2:03 pm UTC

With a R-bomb use in ground-to-ground (or even air-to-ground combat) though, it's basically a hitscan weapon, even in range of hundred of kilometers...Dead zone would sprout everywhere though.

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Re: Science-based what-if questions

Postby p1t1o » Thu Mar 23, 2017 2:08 pm UTC

In other words -

A 9mm pistol would be useless targeting something on the other side of the world, and so would a relativistic weapon.

At some point, putting more energy into your projectile *lowers* effectiveness as a weapon, just as much as if you put 3 pounds of C4 into your 9mm instead of a few grains of cordite.

On the plus side, if you have a relativistic weapon, then you easily have access to enough energy to quickly put yourself in space above the target and to return quickly to where you were. The recoil on a relativistic rifle would be enough to propel you to escape velocity, I'd wager. If you survive the blast, that is.

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Re: Relativistic ballistic problem and factor

Postby gmalivuk » Thu Mar 23, 2017 2:09 pm UTC

andykhang wrote:I don't said it's a planet-based combat though, but just regular ground combat
That's what I mean by "planet-based". As in, it's combat that takes place entirely on a planet.
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Re: Science-based what-if questions

Postby andykhang » Thu Mar 23, 2017 2:15 pm UTC

That kind of high-speed maneuver though is a tad too high-end for an SF though, and reach territory of fantasy( then again, that's basically what I write so what the heck).

On the case of R-bomb in air though, are you sure that rule still apply and not, said, trigger a nuclear chain reaction or something?

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Re: Relativistic ballistic problem and factor

Postby andykhang » Thu Mar 23, 2017 2:20 pm UTC

gmalivuk wrote:
andykhang wrote:I don't said it's a planet-based combat though, but just regular ground combat
That's what I mean by "planet-based". As in, it's combat that takes place entirely on a planet.


Oh that. In that case of a fight take place across a planet, indeed it would be more effective to shoot it from space or even from the moon (though that would mean it's basically a sitting duck on a giant billboard). On satelite though, thing like orbit period and debris would be important I guess.

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How to build a golden house

Postby andykhang » Sat Apr 08, 2017 3:31 pm UTC

Ask title said. I heard that pure gold are too soft for construction work, but would impurity help it to have enough strength for it, and if so, what kind? Also, what kind of thing you need to do to build it when you have enough material and tools you need?

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Re: How to build a golden house

Postby cyanyoshi » Mon Apr 10, 2017 1:14 am UTC

andykhang wrote:Ask title said. I heard that pure gold are too soft for construction work, but would impurity help it to have enough strength for it, and if so, what kind? Also, what kind of thing you need to do to build it when you have enough material and tools you need?

There are lots of problems with pure gold as a building material. Not only is it extremely malleable, but it's also very dense (over twice as dense as iron), meaning that it would have to support more weight than usual. Gold coins and jewelry often contain other metals such as silver or nickel to increase durability, so similar alloys may work as a building material also. However if you want to build something that looks like gold without all of its drawbacks, gold plating is probably the way to go. The less gold you can use, the better.
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Re: How to build a golden house

Postby Eebster the Great » Mon Apr 10, 2017 5:01 am UTC

cyanyoshi wrote:Gold coins and jewelry oftenalmost always contain other metals such as silver or nickel to increase durability, so similar alloys may work as a building material also.

The thing is Andy, like buildings, jewelry and coins have to last a long time given the high cost of replacement. That's why you very rarely see "24 carat" (near 100% pure) gold used in them.

Gold isn't that soft like people often say (though it is softer than most metals), but you still want your chains and rings to resist scratches when possible, and it is far too malleable to be practical for coinage in its pure form.

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Re: Science-based what-if questions

Postby andykhang » Tue Apr 11, 2017 7:16 am UTC

So how would you build this house with gold?

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Re: Science-based what-if questions

Postby Copper Bezel » Tue Apr 11, 2017 7:43 am UTC

It's a matter of taste at that point what counts. A solid gold house will not stand. An ordinary house with aluminum siding plated with gold leaf isn't very interesting. What you want is somewhere in between those extremes, but it's entirely up to your preference in this hypothetical. Especially since you specify a "house" rather than, say, a "freestanding structure", which would be more about the physics of construction. I'm picturing a gold house in the suburbs with the front door painted gold, a two-gold-car garage, and a little gold picket fence around the well-trimmed gold lawn.
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

she / her / her

p1t1o
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Re: Science-based what-if questions

Postby p1t1o » Tue Apr 11, 2017 8:31 am UTC

A house built out of solid gold has to be built in the shape of a giant Sphinx. Them's the rules.


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