A physics logical problem - Page 1
Forum section: electronics / general

author: msuffidy
author_rank: Frequent Contributor
timestamp: December 24, 2020, 05:38:01 pm
content: This is probably not the greatest place to be asking this, but this forum is such that I can just introduce a topic and not add on to an existing topic.OK so I was watching 'The Expanse' and as far as I understand they are suggesting they used some asteroids as a kinetic weapon of nuclear bomb levels of energy. It is not my question, but the way the asteroid like made a right angle change in direction when it approached the Sun and broke apart, suggests it did have the energy levels needed. It may have made a gravity assist or two.OK so this is the logical problem I was looking at:Let's say you have a small object, like a marble, and you keep putting energy into accelerating it. Since you can never get to the speed of light, you can put any arbitrary amount of energy into its momentum. So say a marble had enough energy to release 100Mt or so when it his something. What effect would collision with the Earth be? I think maybe it could even be significant, just that maybe this scenario does not naturally occur by say supernova; it would require a dedicated sustained application of energy.Also I was saying that nuclear bomb level energy kinetic collisions could at least radiate matter in the form of high temperature EM emission. Some people were really offended when I suggested kinetic collisions could cause radiation.

author: vad
author_rank: Frequent Contributor
timestamp: December 24, 2020, 07:11:09 pm
content: Quote from: msuffidy on December 24, 2020, 05:38:01 pmThat’s what they actually do in particle accelerators: transform kinetic energy into radiation and matter.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 24, 2020, 08:06:32 pm
content: In principle an object can be accelerated a lot, however as it gets faster and faster the machine also needs to get larger and larger. It gets increasingly difficult when the energy gets high.Things are easier with particle accelerators, as charges particles can be forced to a more or less circular track and thus reuse the same part multiple times. The relatively high charge to weight ratio helps to apply force via an electromagnetic field.Even a moderate collision (e.g. clapping the hands) can cause radiation - it's called sound.With enough energy concentrated to a small area the temperature will get high enough so that the normal thermal radiation can extend all the way to the X-ray range. This can already happen during the collapse of a suitable small bubble of gas in a liquid. There is crab that can cause such bubble collapse and this way produce X-rays - though only low intensity and a short burst.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: December 24, 2020, 08:41:55 pm
content: Kinetic collision most certainly can produce radiation. I think you could easily get those other people to agree that a high velocity bullet striking a steel plate will produce some sparks. The light we see from those sparks is radiation. Granted, in this case it's not ionizing radiation (what they probably consider as "radiation"), but there is no fundamental difference between ionizing radiation and visible light. They are both on the same spectrum of the same physical phenomenon, ionizing radiation just happens to be of higher energy, which is no problem since we are considering the collision to have arbitrarily high energy; which brings us to the problem at hand - relativistic impacts.Of course, the physics of this sort of multi megaton collisions are not something that is taught in high school, since processes involved here are not physical, but nuclear, in the strictest sense of the word. Aerodynamics don't play the part here, there just is not enough time for air to move aside and let the object pass. In fact, the object hitting a planetary atmosphere will undergo nuclear fusion as the air molecules and atoms slam into the molecules and atoms of the object. Atomic nuclei will fuse, then break apart in whatever fashion this particular fusion occurs, but in the process will emit gamma, x, and all sort of other nasty rays.As for effects on the planet, a 100 Mt marble will have roughly the same effect as a 100 Mt nuclear weapon. Energy is energy. The only difference will be in the composition of the radioactive fallout, depending on the composition of the marble, but the blast and explosion are the same.Optional read:Relativistic baseball, by xkcd

author: IanB
author_rank: Super Contributor
timestamp: December 24, 2020, 09:35:16 pm
content: There are some explanations and equations here that illustrate the theory:http://hyperphysics.phy-astr.gsu.edu/hbase/inecol.html#c1The summary is that if a small object like an asteroid strikes a large object like the Earth, then almost all of the kinetic energy of the small object is lost (transformed into other forms of energy). In practical terms the kinetic energy is transformed into heat and the impact is like a bomb going off.If people object to the idea of radiation being produced, they are failing to appreciate that heat and light are forms of EM radiation. Maybe remind them of shooting stars (meteors). Lots of heat and light there, produced exactly by the kinetic energy of asteroids being converted to heat due to collision with the atmosphere.Most meteors probably are the size of marbles, and they never reach the ground. If they are big enough, they do. If they are very big, they can cause mass extinction events on Earth, like the one that wiped out the dinosaurs. That impact would not just have been a big bang. It would have been a massive fireball, like a million nuclear bombs going off at once.

author: David Hess
author_rank: Super Contributor
timestamp: December 25, 2020, 12:00:11 am
content: Start here under Kinetic Kill Weapons:http://www.projectrho.com/public_html/rocket/spacegunconvent.phpAn object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT.- Rick RobinsonOnce you get up to 200 km/sec, the yield is approximately the same as a nuclear weapon weighing the same amount.For large objects, do not count on the atmosphere being any help for shielding. Above a certain size, it ceases to matter whether the target has an atmosphere or not because the object does not spend enough time in the atmosphere to matter.

author: GlennSprigg
author_rank: Super Contributor
timestamp: December 25, 2020, 02:15:56 pm
content: There are so many 'particles' that routinely hit & pass right through 'us' and Earth.Occasionally, Astronauts report such 'flashes in the eye', but still leave them Alive!When such 'particles' strike the Earth, and often do, the point is their Size & Speed!'Particles' that we describe as 'Meteors' for example, are still traveling Relatively slow, inregards to what is being discussed here! And people often don't grasp how small they canactually/typically be. We may see a large blazing trail of light, that was typically the mere sizeof a Pea. The vast majority of the 'night flashes' we see are but the size of a grain of sand!!However, at much moremassivespeeds they can literally pass right through Earth, likea bullet passing through a cardboard box, without disrupting the mass/inertia of such a recipient!

author: msuffidy
author_rank: Frequent Contributor
timestamp: December 25, 2020, 03:29:42 pm
content: I thought what may happen in extreme cases is they instantly make things molten around the edge and just go straight through. But there could be a tendency to proliferate outwards. Also near relativistic objects are supposed to have a slower time in their frame so maybe it can hold out longer. Maybe sometimes it makes a small hole and does not get all the way through.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 25, 2020, 04:17:10 pm
content: Approximately something like this:https://what-if.xkcd.com/1/He doesn't give the Mt equivalent, but it seems to be around 4Mt (see:https://en.wikipedia.org/wiki/Baseball_(ball)http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.htmlhttps://www.google.com/search?q=1.6865393848798+x+10%5E16+joules+in+tonnes+of+tnt)For comparison, a marble is around 6.5g, I guess. So it will definitely be relativistic.I'm a bit curious about how you propose to put energy into it -- at some point, whatever mechanism is used to accelerate it (in orbit, or by increasing its energy), will also cause it to radiate quite a bit of energy. (I'm not sure exactly how this would arise for a neutral object; if nothing else, it will radiate somewhat Doppler-shifted black body radiation, and (even weaker still?) gravitational waves. Possibly a neutral object could be "pumped" with reflected laser light. More practical would be electromagnetic propulsion, which would entail the object having some kind of dipole moment or charge, which in turn is also able to radiate.)As for impact:At gamma = 72.6, this "marble" is thoroughly relativistic (0.001% below the speed of light). I use quotes, because it isn't very much relevant what it's made of, anymore. Its component ions alone (mostly oxygen and silicon, for a typical glass marble) have energies of around 4 TeV -- giving the LHC a run for its money, but needless to say, vastly outpacing its luminosity (typical beam current is... something like 100s trillion of particles/sec?). Though the LHC does have a finer focus (~0.3mm across).The LHC uses a beam dump made of solid graphite, a cylinder seven meters long. When the beam is decelerated, it's diverted away from the main ring, and scanned over this block, distributing the heat. In an instant, the whole block jumps suddenly as it absorbs the beam momentum, expands from the instant heat wave, and absorbs, probably every imaginable nuclear reaction and byproduct. (Likely ranging from spallation products of former carbon atoms, to fusion products pretty much anywhere on the periodic table, and the effect from whatever strange baryons arise from the quark-gluon plasma formed at the instant of every impact. Which all pretty quickly decay to protons and neutrons, so, mainly activation products.)Which makes this comic, eerily plausible:https://xkcd.com/401/(Assuming, of course, the beam weren't trapped under a hundred metres of rock, but could be pointed into the atmosphere, allowing it to travel enough distance that it could plausibly hit a very low-flying, and very unlucky, helicopter.)Anyway, the marble would probably have a similar trajectory. I'm not sure how far it would plow through the atmosphere itself; if that's the end of it, well, that's one incredibly hot column of what-used-to-be-gas, expanding like a laser-straight lightning bolt at all levels of the atmosphere, a linear Tzar Bomba. Needless to say, nearby cities or forests wouldn't survive, the blast wave will be felt around the Earth, and the mushroom cloud will carry dust to altitudes rarely seen, causing some days or months of haze and possible cooling.And some amount of atmospheric fusion, which will increase the yield. xkcd doesn't speculate on the amount, though he gives "a few rounds" per collision. So, if the collision volume is known, that would give some estimate. The yield from nitrogen and oxygen, all the way to iron, is not much less than the yield from uranium fission, actually. It's not clear how close to iron it might get, but at least part of the way there (e.g. 16O + 16O --> 32S) is going to be a not-insignificant amount. So, add in some light-isotope nuclear fallout as well (of which, 16O + 28Si --> 44Ti is probably the most important?).And again, since we're talking ultra-relativistic particle-collider energies here, there'll be plenty of quark-soup and spallation and activation of assorted isotopes, in addition to the obvious nitrogen, oxygen, silicon, and adducts thereof.If it penetrates the atmosphere and reaches the ground, much the same happens, with some amount of earth also being moved (cratered) by the intense and sudden heating. Include additional isotopes, and much more fallout (since there's dense solid matter, and heavier isotopes, to be activated and fused this time).Tim