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Mar
20
comment Excitations implied by symmetries
Thanks for this explanation, it really helps me. Can you point out more specifically what would not work in the case where the symmetry is not broken (i.e. you still have homogeneity or isotropy), and what would not work if the symmetry broken were discrete? Thank you very much.
Mar
19
comment Direct comparison of energy measurements for kids
Thanks your comment. Could you please also give me some advice about the physics? I see that you think I am not prepared to teach these subject (in fact I am a unit developer for this project, therefore I will not teach it myself, but a physics teacher will). Could you please specify what makes you think so and what in my observations gives you this impression? I am not up for any polemics, but I think your opinion could really help. Thanks!
Mar
2
comment Stability of plants and buildings: the role of the xylem
I am feathering my own nest, but the question is about the physics of the natural system in question, not about the way to engineer, improve or optimise the stability of the system for itself.
Dec
6
comment Earth as a conductor
Thanks for the comment. I specified a little bit better which cases I am referring to :)
Mar
5
comment Why is a hexagon such a stable shape for materials?
math.stackexchange.com/questions/509063/…
Feb
10
comment Can a liquid boil in a closed container?
Isn't this approximately what happens in a pressure cooker?
Feb
7
comment Application of Bernoulli's theorem
@pcforgeek I edited the answer to clarify it. Hope it is clear now.
Jan
30
comment Poisson equation in 2D and 3D: geometrical reason for the difference
Thanks. It sounds pretty clear. But it seems to rely on the fact that I am allowed to have $F=\nabla\phi$, whilst the mathematical equation for $\phi$ alone has already this property. Does that present any limitation to this argument?
Jan
28
comment Laplace equation between circles
Yes, you're right. Could you do anything to migrate it?
Dec
19
comment Why (and how) do foods stick to a pan?
@JohnRennie I do not agree, take for example lubrication, the tendency for protein-rich foods to stick more easily, etc. I am asking what is the physical counterpart of the bond-dominated explanation that chemist would give.
Jul
9
comment Frequency of the sound when blowing in a bottle
@BeniBogosel I think that the phenomenon you describe happens because the different angulation causes a different area of the opening port to be exposed to your blowing.
Jun
24
comment Walking & Swinging
@JohnRennie "...reduces the torque on the body and therefore makes it twist less". Is there a way to show this formally, without relying on experimental data?
Oct
25
comment Free energy variations
If I understand, it becomes $\frac{\partial f}{\partial p_{i}}-\sum\partial_{j}\frac{\partial f}{\partial\partial_{j}p_i}$, is that true?
Oct
24
comment Free energy variations
Thanks, and if $f=f(r,p(r),\nabla\cdot p(r), \nabla\times p(r))$?
Jul
16
comment Why and how is sound produced when two objects hit each other?
Thanks for the answer. So, when two stones hit each other and they are in my hands, each one make the other vibrate by means of the impulse given and this vibration is trasmitted to the surrounding air to produce an audible wave pressure? I mean, can I neglect the detailed "solid" effects and just consider every collision as a source of vibration of the objects (even if the vibration is partially suppressed as in the case of my hands on the stones) ?
Jul
14
comment Glass - paper: Stevin's Law
Yes, I figured this. So, now I am wondering if the effect I described in the question is the main responsible of the non-fall of the paper, or if the surface tension (for small radius of the glass) is much more important as some people say explaining this experiment, and as confirmed by the fail with a bigger surface. In fact, with a bigger surface, the pressure effect should be the same (actually even better because of the less importance of border effects) but the surface tension becomes irrelevant.
Jul
14
comment Does Newtonian mechanics predict the bending of the course of light by objects with mass?
@Peter I don't understand why a particle without mass, in Newton theory where the interaction is supposed to be proportional to both the masses of the particles considered, should feel a gravitational field. Could you pleas clarify this point?
Jul
14
comment Glass - paper: Stevin's Law
Can I also ask you how much does the surface tension matters? Actually, I expect that with a big tank this same experiment doesn't work. Is that true?
Jul
14
comment Why and how is sound produced when two objects hit each other?
So, some collisions are louder than others just because they cause a bigger local variation of pressure (which then propagates through air until finally gets heard). Right? So, why some objects, even if the velocity before and after the collision seems to be the same, are louder than others? I mean, how do the different material properties enter in the phenomenon?
Jul
11
comment Glass - paper: Stevin's Law
Sorry, voilà here it is!