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The universe now is expanding but its momentum will end and it will stop expanding and a reverse action will occur due to the force of gravitation . It is then when all the universe will shift gear backwards . Thus reversing the motion of the constellations , their stars and their planets . No body knows the speed of the expansion of universe or when it will ...

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Imagine you have a hot tub, and you heat it up to a nice toasty temperature. Then the power goes out. The metabolism of the hot tub environment is now zero. It won't get any warmer. But if you get in the tub, you'll still warm up. The thermal mass of the water won't be cooled much by you entering. You're taking advantage of the heat that was produced ...

9

As you say, the power produced per cubic metre of the Sun's core is surprisingly low. This is because proton-proton fusion is a very slow process, as has been discussed hereabouts before. The core is so hot because conduction of heat through the core is slow. The average speed with which a photon escapes the core is the astonishingly low value of about ...

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If you were to "magically" place a planet in the sun's core, I'm fairly sure that is would not be there long. The ambient temperature of the sun's core is somewhere around 15.7 million K, as you said. You should think about why its so how there before you think about melting planets. The density of the core is something like 150 times denser than water. When ...

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The first the expression $U(r) = -\frac {GM} r$ is a potential, but not potential energy. The units are velocity2. This is a widely used potential in solar system astronomy, geology, geophysics, and in aerospace engineering. For example, see ...

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Notice that $h$ and $r$ are related in the following way: \begin{align} r = R + h \end{align} where $R$ is the radius of the Earth (the distance from the center to the surface) and $h$ is the height above the surface. Then notice that \begin{align} U = -\frac{GmM}{r} = -\frac{GMm}{R+h} = -\frac{GMm}{R}\left[1 -\frac{h}{R} + O(\frac{h}{R})^2\right]. ...

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No. As @Jim said, the heat would weaken the rock, which would cause a tunnel collapse before any sublimation could occur. Also, remember that the air in the tunnel would generally be at the same temperature as the rock (unless a large cooling system was put in), so thermal equilibrium would be maintained without any sublimation.

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Correct. For a sphere of uniform density, the acceleration drops off linearly. $$g = g_{surface} \frac{r}{R}$$ where $r$ is the location under consideration, $R$ is the radius of the sphere and $r < R$. Under such a scheme, gravity would be one half that at the surface. The earth is not a uniform sphere though. The outer crust is much less dense than ...

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In this, I have taken the assumption that the singularity is created within the atmosphere, perhaps by an experiment or some such, rather than a wandering black hole, and therefore starts life with much less mass than the earth. A naturally created black hole travelling in space would generally be far more massive, having been created from a collapsing star. ...

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Reformulating your question: do metals feel a force of attraction to the earth due to the earth's magnetic field - and does that force depend on the position on earth? It is not the magnetic field itself that causes the attraction, it is the gradient of the magnetic field. In a uniform magnetic field you will get some magnetization (more so in ferromagnetic ...

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Some key reading if you want to understand this stuff is chapters two to five of the IERS Technical Note 36, the IERS Conventions (2010). It's not just the J2000/FK5 frame (aka the EME2000 frame) that is associated with some epoch date. Every Earth-centered inertial frame has some epoch date. There are two fundamental reasons why this must be the case: ...

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As a visual demonstration of Luboš Motl's answer, this: Image obtained using Climate Reanalyzer (http://cci-reanalyzer.org), Climate Change Institute, University of Maine, USA. is the average surface temperature on earth for 2013. This: is the solar flux by Luboš' formula. And here: I've tried to replicate their crazy color scheme. The point is, ...

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The University of Arizona had a neat website that addressed precisely such questions. It's moved here now. You can choose all kinds of parameters - kind of projectile (ice / rock), impact angle, velocity, landing site and get a prognostication, expected damage etc. Really cool stuff.

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First of all, there are no Moon-sized asteroids in the (sufficiently inner) Solar System. The largest asteroid has radius 450 km which is about 4 times smaller (64 times smaller volume) than the Moon. Moons of planets are not counted as asteroids. A collision with a Moon-sized object would of course be a terminating catastrophe for the Earth. If you look at ...

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