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[Urist Imiknorris]

His son.

[Leafsnail]

Nonsensical. Even an infinite amount of energy only causes something to approach the speed of light and no further.

Hmm.  The idea is that more energy will get you closer and closer to it but never to it.  So one way of saying that mathematically is that as the energy put in tends to infinity, the speed tends to the speed of light (at least that's my understanding of it).  Of course, that doesn't mean you'll ever get there...

[irmo]

Il Palazzo made a much better point than me, but I will go back to my point.
Say you have a wall. You have a small, but non-zero and non infinitely small chance to waltz right through it. The property does apply on large scales, albeit very rarely. Whether it works or not is proportionate to how much energy is involved, how large scale the tunneler is, and what is being tunneled through. If you are putting more energy to moving something than what is needed to make it go light speed, then presumably, you are putting a damn large amount of energy into it.

The energy needed to make any mass go light speed is infinite, so a "damn large amount of energy" still won't make it exceed the speed of light. And tunneling doesn't work by just slamming energy into the particles so that they cross the energy barrier; that's plain old ionization (for electrons), or melting and evaporation (for molecules). Tunneling is special because the particles cross a barrier they don't actually have enough energy to cross.

This of course assumes the scissors are completely rigid.

And that's one reason there are no completely rigid solids in reality. The speed of sound inside one (that is, how quickly mechanical force would be transmitted down the length of the scissors) would be infinite, and thus you could transmit energy faster than the speed of light. Relativistic physics says that's impossible.

Assume a very stiff bar in which you can transmit a sound wave. You tap on one end of this, causing the atoms to jump forward at almost the speed of light. In the reference frame of those atoms, the rest of the bar is moving at almost the speed of light, so its atoms are closer together and individually have higher mass, giving it higher density. Speed of sound in a material varies inversely with the square root of density, so the speed of sound is much higher for the "base" of the wave than for the peak. This smears the wave out until the particle velocities are non-relativistic.

[G-Flex]

Nonsensical. Even an infinite amount of energy only causes something to approach the speed of light and no further.

Hmm.  The idea is that more energy will get you closer and closer to it but never to it.  So one way of saying that mathematically is that as the energy put in tends to infinity, the speed tends to the speed of light (at least that's my understanding of it).  Of course, that doesn't mean you'll ever get there...

This is true. If you were to graph kinetic energy vs. velocity, there would be an asymptote at v=c. You keep getting closer to the speed of light, but at no point, even at infinity, do you surpass it; you just get infinitely close.

[Il Palazzo]

O.k., this is gonna be easy-ish.

As far as our sensory processess go, when a thunderbolt strikes, the lightening is an instantenous flash of light along it's whole lenght.
Why is then the sound of thunder stretched in time over few seconds?

[Vector]

Well, we know lightning is not in fact all one movement.  It is a process.

We can extrapolate from this to say that the speed of light is causing us to perceive this process as an instantaneous effect, while the slower speed of sound causes the event to appear slower.

(... This is a terrible explanation, but if I were explaining this to you in real life you'd be getting a useless picture of cones and a lot of odd noises.  Be glad I'm at least this coherent over the internet)

[Il Palazzo]

Hmmm. While the conclusion is close to the target, the point from which you draw it is irrelevant.

When I said "as far as our sensory processess go", I meant that the process of the creation of this phenomenon can be treated as instanteous, because even though it takes some nano(micro, pico, whatever)seconds of time to pull the electrons alongside the plasma channel and whatnot, from our brains' perspective it's an instantenous event. There's a very limited resolution of time that our brains are capable of percieving(~1/24th of a second iirc, but I digress).

So, you've got an instantenous physical occurence, which emits light and sound at roughly the same moment. Yet, you see it all at once, but hear a prolonged sound.

[Vector]

Yeah... as I said, I don't think I'll be able to give the actual explanation I have in my head for this, because it involves a lot more intuition than it does Fact.  But, thanks for the interesting thought experiment.

[Solifuge]

Reviewing what I know of lightning and thunder, it's created by a massive electrical discharge, which superheats the air it passes through due to the resistance of the air molecules. The superheated air expands out in a burst due to the sudden addition of heat energy, causing it to compress/expand and create a sound wave.

I'd guess that the duration of thunder is due to the air's compression not being an instantaneous event; the heat energy remains, though the expansion slows as more of it is turned into mechanical energy. The lingering soft rumbling is probably the sound of all the tiny claps of air echoing off of terrain for miles around.

[Il Palazzo]

You're right with the rumbling. The compression, while certainly not instanteous, is supersonic(that's why it's so loud), which, considering the very limited cross-section of a thunderbolt, would not give off such a long lasting sound.

[Leafsnail]

Well, I have one.

Why do mirrors reverse seem to reverse left and right, but not up and down?  It's... quite easy to see the answer, but quite hard to explain it coherently.

[Darvi]

They do reverse up and down. If you hold them horizontally.

[Il Palazzo]

Well, I have one.

Why do mirrors reverse seem to reverse left and right, but not up and down?  It's... quite easy to see the answer, but quite hard to explain it coherently.

The answer is: because they do neither and we're a laterally symmetrical species.
What a mirror does, is preserve left/right and up/down, while reversing front/back. This is all it really "does". Now, if we ask our brains to take the resulting picture and rearrange it, by imagining that we stand facing in the same direction that the reflection does(restoring the front/back direction), we can do it either by turning our imaginary selves left-right, or up-down. We preffer left/right, because we're laterally symmetrical, so that the resulting rearranged image still makes sense to our brain - it still has one hand on each side, and still stands with it's feet on the ground etc.
If we were a race of sentient chinaware dishes, we would have no such prefference, as we would be both left/right and up/down symmetrical. Then we would be saying that a mirror can do either, but never both at once.

Mathematically speaking, the mirror changes the handedness(I just hope that I'm translating these terms properly) of the reflection's refference system, so e.g. the typical left-handed* cartesian system becomes right-handed.
Other than that, it's all our brains' doing.

Spoiler: No explanation like a drawn explanation (click to show/hide)

[Leafsnail]

New physics question.  Probably less vague than the last one.  The hint I'll give you is be really, really careful about units.

Spoiler (click to show/hide)

[Darvi]

Welp, since E kin=(m*v^2)/2, and since (E kin)' is a constant, and m is also constant, I assume that it's A.

Although, I dunno how friction works, so I might be wrong.