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seen Sep 4 at 18:03

Phd student


Jun
22
comment electron orbits
@dmckee: I did say it was a simplistic answer ;-)
Jun
22
comment Ascent rate and size of balloon
@Cameron: You could calculate a rough estimate by doing a little experiment - Get one of the balloons you intend to use and inflate it until it pops. If you know the pressure difference between inside and out when it pops, you could predict at what height this same pressure difference would occur. Since measuring the pressure in the balloon may be difficult in practise, you could calculate it if you measured the size and (negative) weight of the balloon, up until the moment it bursts.
Jun
22
comment electron orbits
A simplistic answer: if a single electron, bound to a proton, absorbs a photon, the electron will be excited into a higher energy state. If the photon absorbed is higher than the ionization energy, the electron will be liberated from the atom. Therefore the highest energy state the electron could occupy, without being ionised, would be the state closest to the ionization energy (from below.)
Jun
22
comment Function of electric water pump
That just depends on which way around you connect the two pipes to it.
Jun
21
comment Energy produced by a swing?
Hi @Seb, the GPE and KE are the two forms the energy could be in. The total energy available in the system is $E=GPE+KE$. When the swing is high it is changing direction, which implies the velocity is zero and therefore the KE is zero. All the total energy is therefore all in the form of the GPE at this moment. When the swing is low, the velocity is maximum, and therefore so is the KE. The GPE is necessarily zero at this point. All of E, GPE and KE are energies - so yes, they are all measured in Joules.
Jun
19
comment a question on Lagrange's equation when the time derivative of the generalized co-ordinates is constant
I see what you're getting at but this is too brief to be an answer. Perhaps you could change it to being a comment or edit your answer to elaborate. -1 until then I'm afraid.
Jun
18
comment Formulas for ball rolling in a bowl?
@Dane: See also this question physics.stackexchange.com/questions/11227/…
Jun
18
comment Analyzing the motion of a ball rolling without slipping inside a hemispherical bowl
Closely related: physics.stackexchange.com/questions/10798/…
Jun
16
comment Does particle indistinguishability and quantised enery levels (in bound states) violate the Pauli Exclusion Principle?
@gigacyan: Having just finished another read-through of this page I wondered whether you would edit your answer to include the essence of our discussion in its comments. After which, I would be happy to accept it :)
Jun
16
comment heliocentricity and the theory of relativity
I would go as far as to say this is a duplicate of the question in @Qmechanic's comment. @statichippo: regarding your last paragraph - indeed, no need to worry about that here :)
Jun
15
comment What happens when two D-branes annihilate?
@Hiatus: To my mind, your comment seems sufficient for an answer.
Jun
15
comment Stronger than Newton's laws?
@Marek: Here, here! I'd vouch for those to comments to be posted as an answer (minus the 1st sentance perhaps ;) Upon seeing it, I will certainly cast a +1 vote on it.
Jun
15
comment Stronger than Newton's laws?
Continued.. I suspect, however, that in practice this would be of very limited use - Newton's Laws work fine as they are and their power, in some respect, comes from their simplicity and ease of use. Given that QFT is already complex enough to solve for elementary particle interactions, it would likely be extremely difficult to show that it can be reduced to Newton's 2nd Law for the many-particle systems, that comprise the macroscopic bodies, to which Newton had intended it to apply. In summary, I don't feel this question is worth losing much sleep over, even if it is solvable analytically
Jun
15
comment Stronger than Newton's laws?
@Vladimir: For the record, I dislike refering to running couplings/masses as an "anti-Newton" law even more than I disliked calling it "t'Hooft's law." QFT and Newtonian mechanics are both fundemental but have very different realms of applicability. Both make firm and accurate predications when used at the appropriate energy scale for which they were developed. Of course, in principle, it should be possible to derive Newton's Laws from QFT. ...
Jun
15
comment Is Palladium an exception?
Nicely done. +1.
Jun
14
comment Is Palladium an exception?
For me, your comment seems to make your original question clearer and more answerable. To which end, I agree with what @Qmechanic has written above (+1.)
Jun
14
comment Stronger than Newton's laws?
I agree with the sentiment of @Rasko's comment. However, I don't think it's appropriate to refer to running masses and couplings as "t'Hooft's law". Perhaps I'm being pedandic, but that's how I feel.
Jun
13
comment Can a planet cover the whole sky as seen from its satellite
@Philip: No, the effect of an atmosphere with increasing density at lower altitutes would increase the extent of the sky covered by the large planet. (Before I wrote it above I too had to take a minute to consider in which direction the light would refract.) Imagine you're standing on the satellite looking at light from the very edge of the planet; almost parallel to the surface of the satellite. As it enters a medium of higher refractive index, at an oblique angle, it will bend towards the normal-to-the-surface. I.e. into the surface of the satellite, thus preventing you from seeing it.
Jun
13
comment Do color-neutral gluons exist?
@Lubosh: Your statement "This is more manifest if..." reminds me a little of when physics text books often say things like 'this easy proof is left to the reader' when in fact the proof would only be easy if the reader happened to be a professional in that particular subject. I've been meaning to ask about the physical significance of diagonal and off-diagonal matrix entries for some time. My reason for not doing so is that I feel it would be a bit too mathsy for physics.SE and visa versa. I would therefore be hugely greatful if you could elaborate on your second paragraph a little.
Jun
13
comment Is Palladium an exception?
What they teach at school level isn't quite the whole truth. Have a read if this wiki page and then see if you have further questions. en.wikipedia.org/wiki/Atomic_orbital