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location Bristol, United Kingdom
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Knowledge and understanding are quite different. Only understanding can lead to being, whereas knowledge is nothing but a passing presence in it. (G.Gurdjieff)


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!
Jul
6
comment Physics of Fireworks
Do you know if is there any more specific reference to the fireworks applications of the plasma processes?
Jul
4
comment Does irrotational imply inviscid?
Done, but I have to disagree on your last sentence. A potential flow is one for which only the condition of irrotationality can arise (and not necessarily the incompressibility). To have a stream function it is enough to have just the incompressibility condition (and not necessarily the irrotationality).
Jul
4
comment Does irrotational imply inviscid?
Do you want me to switch in my auto-answer?
Jul
3
comment Rotation of parabola
I edited, maybe this is more clear! Isn't it?