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| A physics logical problem |
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| msuffidy:
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. |
| vad:
--- Quote from: msuffidy on December 24, 2020, 05:38:01 pm ---Some people were really offended when I suggested kinetic collisions could cause radiation. --- End quote --- That’s what they actually do in particle accelerators: transform kinetic energy into radiation and matter. |
| Kleinstein:
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. |
| Domagoj T:
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 |
| IanB:
There are some explanations and equations here that illustrate the theory: http://hyperphysics.phy-astr.gsu.edu/hbase/inecol.html#c1 The 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. |
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