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Dec
31
comment If I toss a coin, vertically, on the surface of Mars, will it land back in my hand?
I, too, don't understand what you're getting at with this question, but at any rate the answer won't depend on whether you do this on Earth or Mars.
Dec
19
comment How many fixed points does a Kelvin scale have?
An affine scale has to have two fixed points. For a linear scale, zero is always mapped to zero.
Nov
1
comment Is it (practically) possible for a large building to be a Faraday cage?
@RobJeffries: sure, if the mesh as a whole is much bigger than the wavelength. Otherwise it's just an inefficient antenna that scatters the waves a bit.
Nov
1
comment Is it (practically) possible for a large building to be a Faraday cage?
Are those meshes usually grounded, though? If not, then they can only shield wavelengths much smaller than the window. So, yeah, probably works for mobile phones, but wouldn't really qualify as a Faraday cage.
Oct
10
comment Why does public mains power use 50-60 Hz and 100-240 V?
@EJP: “I've heard an 8Hz note on a pipe organ” – I doubt it; such low frequencies are pretty much only felt in the body! What you do hear though, from an $8\:\mathrm{Hz}$ organ note, are the overtones; after all an organ doesn't produce a sinusoidal signal. And even though mains voltage is a lot closer to being sinusoidal, it's usually not so much $50\:\mathrm{Hz}$ itself that's a problem in audio applications (you can tackle that quite efficiently with notch filters), as the overtones (which need a more intrusive comb filter).
Aug
13
comment Halley's Comet as a “Free Taxi”
“fundamental misunderstanding as to how movement in space works” — what-if.xkcd.com/58.
Aug
5
awarded  Nice Answer
Jul
26
revised Breaking the sound barrier underwater
Typos
Jul
26
revised Breaking the sound barrier underwater
added 401 characters in body
Jul
26
answered Breaking the sound barrier underwater
Jul
26
revised Why do shadows from the sun join each other when near enough?
Re-host GIMP file on Dropbox, since Ubuntu One has been discontinued.
Jul
21
comment How can one derive the Ohm's Law?
The Drude model is definitely the best answer to this question, +1.
Jul
21
comment How can one derive the Ohm's Law?
Uh... how does the water-flow analogy imply that $U \propto I$? (That is actually valid for a purely laminar flow, but who says it makes sense to assume high viscosity for the water-flow model?)
Jul
15
comment Is Dark Matter expected to be equally distributed in our solar system?
@RobJeffries: I'd say $\pm1.5\:\%$ still qualifies as “pretty uniform”. But the prediction of that variation is really cool!
Jul
12
comment Which one to learn first: Special or general relativity?
Or to place that analogy somewhere else: it would be like making a full motorcycle driver's license without first learning to ride a bicycle.
Jul
8
comment Quantization vs. continuous energy levels
You do get a truely continuous spectrum in a gas if you make the interactions strong enough. Enough temperature & pressure... that's basically why the sun is a black-body.
Jun
29
awarded  Nice Answer
Jun
16
revised Why and how does negative velocity exist?
LaTeX math parts
Jun
16
comment Why and how does negative velocity exist?
This is IMO a better answer than the accepted one: there is no such thing as a negative vector, there's only vectors with direction that happens in some basis to have negative coefficients.
Jun
10
comment What exactly is a dimension?
@TemplateRex: to be pedantic, the guy's called Gram, not Gramm...