# queueoverflow

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bio website martin-ueding.de location Germany age member for 2 years, 6 months seen Apr 4 at 18:59 profile views 171

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 Mar26 answered Why is the Gibbs Free Energy $F-HM$? Mar26 comment Why are 3 different road tests enough to say the suspension system of a car can handle any random road? I guess that you have to check whether the suspension has an eigenfrequency (a resonance frequency) that is in the range of those roads. And you have to check that it is not under-damped. Mar26 awarded Notable Question Mar24 comment Finding angular momentum about the center of mass? Sounds like you did it right. Rearranging and integrating is what I would have done as well. Mar23 comment Finding angular momentum about the center of mass? You are just looking in 2D here. So angular momentum will be just a number. Angular momentum will be directed in $\mathbf z$-direction, which you did not introduce yet. But since $\mathbf x \times \mathbf y = \mathbf z$, you will get that with the right-hand-rule. $\vec L = m \vec r \times \vec v$. So angular momentum is perpendicular to both the separation as well as to the velocity. Mar23 comment Finding angular momentum about the center of mass? Now we are talking. Here is your roadmap: Express $L$ in terms of $t$ and $\dot \theta(t)$. How to do this should be written about. Then you want that $L$ is a constant. Solve the differential equation for $\theta(t)$. Since the momentum is constant and the distance between the masses is shrinking, the speed will go up. You will end up with some polynom for $\theta(t)$, I think. Mar22 comment Finding angular momentum about the center of mass? You need to find out what is given, what depends on the time and what $\theta$ is supposed to mean in your problem. Before you do that, we will not get any further. Mar22 comment Finding angular momentum about the center of mass? Your system is like a barbell that is rotating. Actually, we only know its rotation angle $\theta(t)$. Since I assume that I can do a time differentiation and get the angular velocity $\omega(t) = \dot\theta(t)$, I can compute $\vec L$ and the energy $E$. But since I needed to know $\theta$, I cannot compute it. Trying to compute $\theta$ does not make sense. You have $\theta(t)$ given. If you did not, and only $L$ or $E$, then it would be like asking: “It is going that fast. Where is it now?” You cannot answer. Mar22 comment Why is the Hodge dual so essential? I have a good picture of what $\vec B$ and $\vec E$ mean physically and what effect they have onto classical charged particles. I do not have a good picture of a two-form, yet. I'd like to, but I think I will have to wait until I did GR to get this. Mar22 comment Finding angular momentum about the center of mass? $I$ is the moment of inertia. Sometimes also $J$ or $\Theta$. I assume that your $\theta$ is an angle. If it was the moment of intertia, that would be surprising. I thought $\theta(t)$ was a given in your problem? If not, you can at least write down $\vec L$ as a function of $\theta$. The arrow means the following: $\vec r = r_x \mathbf x + r_y \mathbf y$. It just means that $r$ has a magnitude and direction, that it is not a plain number. Mar22 answered Finding angular momentum about the center of mass? Mar22 comment electron pathways Your idea does not sound bad. Only if that happens, you will have a steady state solution to the problem. Mar21 comment Which properties of electricity and magnetism are responsible for the speed of light being what it is? As far as I have understood, vacuum has permittivity $\varepsilon_0$ and permeability $\mu_0$. That means that just like it takes time to charge a conductor or put a current through a solenoid, it takes a little time to create a field in the vacuum. Therefore, the propagation happens at the speed of $c = 1/\sqrt{\varepsilon_0 \mu_0}$. Mar21 comment Why there is no “Edison” unit in physics? @dmckee I read it twice, yet I do not see what you mean :-/. Or is “inductance” and “inductivity” the same thing? I am German, and for me, “Induktion” and “Induktivität” are distinct things. Mar21 answered When combining three spin $\frac{1}{2}$ particles what are the corresponding states? Mar21 comment Free fall time with non uniform acceleration and some initial velocity Try starting with the derivation given here and add a $\dot r = ...$ at the appropriate point. Mar21 comment Quantum mechanics and atomic bonding What I mean is that the hamiltonian $\hat H$ will not be rotationally symmetric any more with two atoms. That will break the symmetry of the wavefunctions. The wavefunction is not centered around the nucleus any more, therefore you have an electric dipole moment. I think this is Van-der-Walls-Forces in essence. Mar21 comment Why there is no “Edison” unit in physics? @dmckee Isn't Henry for inductance ($L$)? Tesla is for the magnetic flux density ($\vec B$). Magnetic field strength is $\vec H$, to be pedantic. Mar21 comment Stuff can't go at the speed of light - in relation to what? There is so much space created (by expansion) between the object and you, that the speed of light is too slow to ever make that distance. Just like it is not possible to pay off dept, if its interest becomes higher than your salary. Mar21 comment Quantum mechanics and atomic bonding That is interesting, do you have a link? The spherical shape only applies if there is nothing there (the system is spherical). As soon as you introduce another atom, it will break the symmetry. Then the atoms will start to have a little dipole moment.