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### Is thermal conductivity correlated with speed of sound in metals?

Right off the bat I should say: thermal conductivity and electrical conductivity are definitely correlated in metals. image source: https://www.doitpoms.ac.uk/tlplib/thermal_electrical/printall.php ...
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### Can speed of light be $c$ in air or other medium?

I know that the speed of light in a vacuum is $c\sim 3\ 10^8\ \mathrm{m/s}$, but I also know that speed of light in a medium (e.g., air) is less than that in vacuum. Special relativity says that ...
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This is the Twin frog paradox. I have two questions. First, what does it mean by there is no rigid body in special relativity? What I have known is that the length can be changed from one frame to ...
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### How long would it take for something really far away, say $300,000,000 \ \text{meters}$, to feel the force from a pull of a rope attached to it?

My friend phrased the original question like this: If I tied a rope to myself and wrapped it all the way around the earth and then pulled (assuming the rope was already taut), which direction would I ...
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### What would happen in this “close to the speed of light” scenario?

Say you had a really long pole made of a super strong material, and at the you turned it through an angle of (for example) 45 degrees. Turning the pole through a small angle at the bottom would ...
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### Thought experiment - faster than speed of light travel [closed]

I came up with a thought experiment and it has been on my mind for quite some time now. Would like to hear the thoughts of others as my wife has no clue what I'm talking about. Given two points of ...
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### Does special relativity predict superluminal speeds?

Assume that we have a long Born-rigid rod with a length $L_0$ in which the speed of light is the ultimate speed for sending information. If there is a tiny missile at the right end of the missile that ...
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### Black holes, and faster than light communication

Lets say we have a black hole that has a diameter > 1 light year and we can somehow push and pull this black hole {though the push and pull itself can never exceed lightspeed of course}.Will the other ...
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### What prevents an orbiting object from getting a speed which is greater than $c$? [duplicate]

Consider an object orbiting around a point with radius $r$ and angular velocity $\omega$. Here its linear velocity is $v=\omega r$. If we choose a large enough $r$ and reasonable $\omega$, $v$ might ...
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### When you push a stick will the end of it respond later than the beginning? Is so what is the fastest material and what forces are involved?

Normally when two people hold a long stick the receiving person would feel at the same time the stick moving when the first person gives the stick a push. But is that in reality exactly the case? ...
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I have some questions about the expansion of the universe: The expansion rate is almost 70 km/s for 1 Mpc, so lets say we have a rigid cylinder having a length of one Mpc. As far as I understand, ...
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### Length contraction of a train

Suppose a train of length $3x~\rm m$ and a tunnel of length $x~\rm m$. When the velocity of train is $282842712.5~\rm m/s$ (from length contraction equation), then its length contracts to $x~\rm m$. ...
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### A theoretical object that doubles in length pushing an object through space [closed]

If you were to have a theoretical object that could double itself along a chain so you would start off with 1 then it doubles to two, four, eight etc eventually the width of the object would be such a ...