# Tag Info

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It is commonly believed that the speed of sound at high densities is bounded from above by $c/\sqrt{3}$, where $c$ is the speed of light. Calculations of this quantity in many theories, ranging from QCD to systems with scale invariance, have all shown it to either stay below or exactly saturate the bound. See the introduction of this paper for a recent ...

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If you have an object immersed in air, then you can calculate the forces on it using Archimedes' principle. There are two forces to consider. Firstly you have the weight of the object, which is simply: $$F_g = mg$$ where $m$ is the mass of the object and $g$ is the acceleration due to gravity. This force acts downwards. Secondly you have the bouyant ...

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Yes. A decent approximation of impact was found by Isaac Newton. Simply put, it is $$D=L\frac{A}{B}$$ where $D$ is depth, $L$ is the length of the projectile, $A$ is the density of the projectile and $B$ is the density of the object being impacted. Velocity doesn't play into it. So double the density of the impacted object and the impact depth will be ...

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Using the Schwarzschild radius for this purpose makes sense, because this is the radius of a sphere which becomes a black hole, if it has the given density. For example a sphere made of air at Earth density does not become a black hole if its radius is 1 meter. But if the radius is big enough, it will actually become a black hole. Even though the density is ...

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A black hole is a region of spacetime enclosed by an event horizon. Thus, the singularity, while a fact about black holes as far as we understand them, is not an defining feature of what black hole is. Therefore, it makes more sense to try to calculate volume (and hence indirectly, density) of a black hole according to the extent of the event horizon rather ...

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In a subsequent video the same person attributes the phenomenon to mercury's high surface tension and non-wetting, non-wicking chemistry. Mercury makes a convex meniscus at the interface between the mercury and a dry surface. The gaps between the salt grains are smaller than the radius of this meniscus, so the mercury can't flow between them to lift them ...

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We can't tell how matter behaves inside a black hole. I can think of at least several solutions, but there is no way to either confirm or deny them. I'd say its most likely matter forms a sphere inside the event horizon equal to the radii of the black hole. Considering physics (as we know it) don't break down inside the black hole, matter can't travel ...

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