Recent comments in /f/askscience

Josephdirte t1_jbad0eb wrote

Reply to comment by Locedamius in How much influence does a natural satellite (like the Moon) have on the formation of continents ? by Aubin_kun

It's been a long while since I studied this stuff, but I believe the heat generated through the natural decay of uranium, with the insulation of earth's rocks, causes differential heating to the interior of the earth, creating convection cycles within the mantle. This drives plate tectonics

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drhunny t1_jbacmpc wrote

Reply to comment by CrazyisNSFW in How do plutonium based atom bombs work? What chemical reactions happen that make them explode? by L0RD_E

the explosive lens is a "lens" in the sense that it can focus shock waves. To compress a sphere into a tiny ball, you have to have continuous equal pressure over the whole surface or else it will deform and splash into a complicated shape.

You cover the plutonium sphere with an shell of explosives (or a shell of some dense metal that is then covered with a shell of explosives.) If you start to detonate the explosive shell using a detonator at one location, the shock wave will hit the plutonium directly under that location first, starting a dimple. The plutonium on the other side isn't being compressed because the explosive there hasn't started to explode because the shock wave hasn't arrived yet.

So you use a bunch of detonators all over the surface. That's better, but it still creates an uneven pattern of pressure -- now maybe you get 20 or 60 dimples forming symmetrically but it's still not going to result in a compressed ball. There will always be locations on the surface of the plutonium where the shock wave is pressing the material sideways instead of inward.

The explosive lens uses two materials with two different speeds at which the shock wave can travel. The shock wave directly under the detonator is going through the slow stuff but the shock wave spreading sideways from the detonator is going through the fast stuff. If you shape these in the right pattern, using curved interfaces, the effect is just like light passing through a curved lens. The shock waves are bent into a pattern that is almost equal pressure everywhere at the surface of the plutonium.

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ivanthekur t1_jbacec0 wrote

Reply to If something happened in the universe that caused a shock wave, would the global population feel Earth move? Would the countries facing the wave experience differ from those on the opposite side? by snow-ninja

When you talk about shock waves on Earth, you're usually referring to particles bumping into each other. Since there are significantly fewer particles in space there's not the same kind of phenomenon for the most part. On the other hand, things can explode in space and because there aren't a lot of particles to slow them down, they just sort of keep going outward from where they started. Any sort of explosion disperses over a distance like a balloon that isn't inflated is much denser, then becomes thinner as you blow more air into it, so most space based explosions have very few particles that reach us on Earth.

About the only two objects in our solar system exploding that would eject material that would hit us noticeably are the Sun due to the sheer amount of mass it possesses and the moon, due to how close we are. The good news is that the sun is pretty stable for a star, and the moon is incredibly inert so either is astronomically improbable. The biggest danger as far as "space shock waves" go is a star or stars going supernova. Our star contains about 99.8% of the mass of our solar system but on a cosmic scale, is not one of the larger stars out there. When a star becomes unstable it can launch an absurd amount of its mass and energy out in a wave. This wave is not a threat to us if it is far enough away, but the closer the supernova, the higher the amount of mass, and the higher the energy the more dangerous it is. A small far away supernova might just be a more visible star in the sky as most of the energy doesn't reach us. A supernova in our immediate vicinity could be powerful enough to bathe our planet in un-survivable radiation. The good news is that most stars near us look fine, we're not expecting any atmosphere stripping shock waves from what we can see of our galactic neighborhood.

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brainwater314 t1_jbac7pj wrote

Reply to comment by BitsAndBobs304 in Does thin stuff placed between pan and induction cooker affect efficiency in a significant manner? by BitsAndBobs304

The slower heating allows heat to leak out while you're not using the pan because it's not hot enough yet, and I'd bet a rag is at least a couple mm thick and would reduce the heating speed noticeably, so I'd say it would reduce the efficiency overall by at least 5% if not 10% or 20%. One of those thin lint free towels would be a better choice.

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