Veeky Forums how do I go about calculating what would happen if a rod moving at relativistic speeds hit the earth? A kinetic strike by, say, a two meter long uranium rod that was two centimeters in diameter.
If it were traveling a significant fraction of the speed of light, say, 50% or 75%, would it really hurt the earth that much, or just go right through it and keep on sailing through space?
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It would have serious problems with the atmosphere. More than likely break up before ground impact, no crater. You'd get wind, some sound, and bits falling. Atmosphere is a real bitch for small stuff, regardless of speed.
You're stupid if you think athmosphere would stop a spear shaped rod of uranium (heaviest metal known to man kind) moving at a significant fraction of the speed of light.
Meteor move maybe at 0.01 % if they're fast
Why the hell would you even assume it could go right through earth? That is absolutely impossible. It probably wouldn't even make it through the atmosphere.
Anyway, the first thing you think about when you are looking at situations like this is energy. Gives you a rough idea what can potentially happen.
The rod you mentioned has a volume of 2513 cm^2 and thus a mass of 48 kg. Let's say it moves at 75% of c. That means that it has an energy (without mass) of about 2.2 EJ which is a LOT. It is equivalent to 529 megatons TNT. That is about ten times the largest nuclear bomb ever detonated (the Tsar bomb). It is pretty much guaranteed that that energy will be set free in the atmosphere and if not (very unlikely) right when it hits the ground. So it won't just be like explained, it will be an enormous explosion.
>Ask a question
>Insult people who answer
Gr8 m8
That's the problem I have. I don't understand how to model collisions well enough. If the rod is going too fast, energy transfer will be low because the rod doesn't interact with the earth long enough. But if it is too slow, then gains could be made by making it just a little faster.
I mean, an ideal impact event would mean the rod never leaves the earth, right? So 100% energy transfer. Or could more damage be done even if the rod passes through the earth and keeps going?
>Why the hell would you even assume it could go right through earth? That is absolutely impossible.
Matter of a given average density only has so much stopping power. I mean you can fire a bullet that goes fast enough to pass through a human, why couldn't a rod pass through a planet if it were going fast enough?
Or are you saying it's impossible because of the size of the rod I specified?
>If the rod is going too fast, energy transfer will be low because the rod doesn't interact with the earth long enough.
That is where you are mistaken. There are a lot of particles to interact with and the rod would get extremely hot, extremely quickly and basically blow up. Then the volume of the rod increases, interaction cross section will get very large und the energy transfer will increase exponentially. It will basically explode in the upper atmosphere.
You are comparing apples to oranges. A bullet moves at very small energies compared to the rod you mentioned so that when it enters a human body, it will stay in one piece. With the rod however friction even with air will be so extreme that it will evaporate in an instant.
The energies are unimaginable, keep that in mind. The temperatures that are being generated by friction alone will probably suffice to trigger nuclear fusion of air molecules.
I didn't ask the question and the user who answered wouldn't have been of any use anyway
Ok so I have a questions that has nothing to do with op but oh well.
The bomb you are talking of has the energy it has "in any direction", right? But what if somehow we channeled that energy through, say, a pipe? Would it increase? By logic it shouldn't, because energy is not dependent on area, but intuitively I feel like it should. Am I just dumb as fuck?
There's no generic mechanism to "channel energy". I guess what you mean is, when a bomb explodes molecules are accelerated into all directions. If they were only accelerated into a single direction, your intuition tells you that the effects such a situation would have on its environment would be much more grave. And it's correct. It doesn't mean that the energy is bigger, it just means that the energy doesn't just diffuse into air. That idea is frequently used, for example building implosions where the bombs are installed in a way that they direct their energy mainly towards parts of the structure. The overall energy in the bombs used in such implosions is not actually that big, it's just smartly used to destroy the structural integrity of the building instead of hollywoodesque fireballs.
>A bullet moves at very small energies compared to the rod you mentioned so that when it enters a human body, it will stay in one piece. With the rod however friction even with air will be so extreme that it will evaporate in an instant.
This is really surprising to me. I wouldn't think heat could travel that fast and the rod could stay intact.
>The temperatures that are being generated by friction alone will probably suffice to trigger nuclear fusion of air molecules.
Well this I could surely calculate. Interesting.
Thanks.
Yes, tsar Bomba released emerge radially in all directions, while the rod would have all of it concentrated on a 2cm diameter surface. Huuuge difference
Interactiion with air wouldn't cause any turbulence at that speed. The rod would just collide with the particles, destroying them or pushing them out of the way too fast for any turbulence to generate
The rod while travelling across the athmosphere would encounter about 12kg of matter, assuming it doesn't interact with stuff around it but just in front of it. It could reduce the momentum a bit, but it would still carry on at relativistic speed
>The rod would just collide with the particles, destroying them or pushing them out of the way too fast for any turbulence to generate
You need to remember that the rod itself is made of particles. When it hits the air molecules not only those will be accelerated, but also the uranium atoms of the rod, which will cause the rod to disintegrate very quickly, in a matter of microseconds.
Let's play phyiscs will ya? Where is the rod disintegrated? In what direction? Because remember that the only thing affetcing the uranium rod momentum are the air particles, which have very very low transfersal momentum compared to the speed of the rod, so that even when disintegrating the particles would keep moving on the same direction. Heat could cause transversal motion buti wonder if you'd generate enough heat to push all those particles a long way from the rod, in the 500 micro seconds it would need to reach the soil.
I also doubt impact with air particles would hurt an uranium rod enough to evaporate all of it, maybe a few centimeters
>Where is the rod disintegrated?
I don't understand that question.
>In what direction?
In all directions. It's a chaotic process. Look up particle showers.
>Because remember that the only thing affetcing the uranium rod momentum are the air particles, which have very very low transfersal momentum compared to the speed of the rod, so that even when disintegrating the particles would keep moving on the same direction.
That is correct, the overall momentum will of course be conserved. The thing is, when the air molecules interact with the uranium atoms, the energies are so high, that it's not just pingpong, it's actual particle physics. You will see a lot of pions and muons emerging and carrying a large part of the energy away into the earth and rest of the atmosphere.
>I also doubt impact with air particles would hurt an uranium rod enough to evaporate all of it, maybe a few centimeters
Air friction even evaporates meteors which travel at a tiny fraction of the energy of that rod. You may say that it has less time to interact with the atmosphere as it's travelling faster, but that makes no sense.
Think: It hits about just as many air molecules as the meteor, just at A LOT higher energies. It's like riding your bike in the rain in the hope that you might not get as wet because you are faster. It's actually the other way around.
The rod will be gone in an instant.
What disintegrates meteors is the plasma envelope that forms around them. At those speed, the rod would leave way behind any plasma before it starts reacting with it's back.
Also running in the rain makes you less wet than walking
I don't think you are quite understanding the energy scale we are looking at here. Compared to what kind of energy those air molecules have relative to the uranium rod, the energies holding together the solid structure of the rod or the ionization energy of the atoms are a joke, plain and simple. Even small deviations from the overall momentum are enough to rip the rod apart like it's butter.
You are actually right about the rain thing.
Btw what-if.xkcd.com
>2m pencil rod
*yawn*
Whatever that program is, I strongly doubt that the results are valid for relativistic speeds such as this.
Absolutely nothing conceived by humanity is valid for anything relativistic.
This is an popsci thread, nothing more.
>if things move fast they're basically ghosts
what the fuck?
>your chosen velocity is higher than the maximum for an object orbiting the sun
Is this Laetitia Casta? I know she did a photoshoot like this but I can't find it anywhere.
It would immediately explode and turn the planet into an asteroid field.
>This is what physicist do in their free time
Glad to see we're all making a useful contribution
I have no idea but now that I put a face to that name I could be convinced it is.
I would kill for a hi-res version of OP pic.
mfw no cow to cuddle
i have an irrational love for cows
they are amazing
...
>You will see a lot of pions and muons emerging and carrying a large part of the energy away into the earth and rest of the atmosphere.
Actually this is an interesting thing to think about. Is there an optimal material for this? For instance, something heavy but below iron so fusion releases some energy rather than taking it?