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 May 7 comment Can we divide two vectors? @JerrySchirmer oops, right. You can only determine the component that's normal to $\vec{B}$. Thanks! May 7 comment Can we divide two vectors? I see nothing wrong with your answer. May 6 comment Why not shoot a marble sized spacecraft at the moon? @Draksis Thanks, I will clarify it. While inertia is not a true force it is sometimes (fluid dynamics useful to refer to it as a force. For example Navier-Stokes equation can be seen as balance of inertial force and pressure, viscuous and other body forces. May 6 comment Why not shoot a marble sized spacecraft at the moon? @Draksis The volume decreases faster than area so surface forces get relatively bigger compared to volume forces like gravity and inertia. Apr 24 comment Was the mass of the universe the same when it first began as it is now? Mass could be understood as the rest mass of all the matter which can change from day to day. I bet you meant the total energy (including mass)...? Apr 23 comment How does conservation work in wormholes? "spacetime curvature involved in a wormhole is qualitatively no different to the spacetime curvature around, for example, the Sun" So there is actually no way to distinguish where is the inside and where is the "normal" spacetime? And I could exchange energies and momenta with that matter at any time during the travel while only conserving the totals, right? Apr 22 comment Mass or no mass? I believe this is the canonical article: arxiv.org/ftp/cond-mat/papers/0509/0509330.pdf It seems unlikely that this speed will be irrelevant of frame... Apr 22 comment Mass or no mass? "Some systems have $m=0$, and these systems always have momentum relative to your inertial frame. Indeed, you will always observe their relative velocity to be precisely $c$." Is it true about the massless electrons of graphene? Aug 27 comment Are orbiting planets an example of perpetual motion? @LubošMotl, but the planets are accelerated all the time, aren't they? Jun 4 comment Total current of two sources in series? @dmckee, as far as Kirchhoff's theory goes, I agree to Will's answer. But maybe you can demonstrate application you had in mind? Jun 4 comment Total current of two sources in series? Yes, that's about as much as I can get out from those equations myself. Jun 4 comment Total current of two sources in series? @Will that is all the information he supplied. May 22 comment What is the effect of humidity in temperature? @user61001, yes, apparent one. If humidity is higher, it seems hotter to people compared to medium or low humidity. May 19 comment What is the effect of humidity in temperature? "Tashkent" is synonymous for "very hot". What's with the outside? I don't really understand the new question. May 19 comment can be exist the negative mass? Physics become interesting when you consider exotic and scifi-like things. Even Newton's second law becomes funny if you consider negative masses :) May 19 comment can be exist the negative mass? And negative masses would attract each other, but repel positive masses, right? That's why they are somewhere far :) May 19 comment Problem with a rotating frame of reference on the South pole @Althalos, there is no centrifugal acceleration on the axis. In which direction could it be there? Your formula is correct, but the $R$ is distance from axis of rotation which is $0$ in your case. May 18 comment Physics of every-day life: rotating bag of tea I think it's just the torque that's stored in the thread... May 18 comment Problem with a rotating frame of reference on the South pole Rotating frame in which train is going straight (as says in the exercise). Yes, $\Omega$ is. Try $\tan(\theta)=F_c/F_a = a/g$. Also $\tan(\theta) = \sin(\theta) = \theta$ (in radians) should for work such a small angle. Apr 28 comment Why does the fundamental mode of a recorder disappear when you blow harder? @Georg, a few years late answer, bet I wanted to add that the higher mode does not slowly overtake. It's a sudden shift of pitch.