# All Questions

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### How to solve the Poisson equation?

Does anyone know how the author in http://gravitationallensing.pbworks.com/w/page/15553257/Strong%20Lensing found the equation $$\kappa(\theta)=\frac{\kappa_{0}}{2\theta}$$ after solving the ...
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### Impossibility of time travel due to energy conservation?

I just watched the movie Terminator Genisys (It wasn't as bad as people say) and started pondering time travel. While pontificating and stretching my limited remembrance of AP Physics, science ...
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### Is special relativity true? [closed]

Is the special theory of relativity true? http://www.npr.org/2014/03/20/291408248/einsteins-lost-theory-discovered-and-its-wrong
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### Are Fe56 or Ni56 the fission products of any binary reactions?

I'm curious as to if there is some combination of a fusion and fission event simultaneously occuring that would only produce 56 nucleon number nuclides. Such that the net energy out of the fusion ...
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### Why does objects with zero acceleraton move?

My question is, if we apply a force on an object to move it with a constant velocity, of course it will move. But what I don't understand is, why will it move? From Newton's law F=ma and in this case ...
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### What does gravitational mass mean if (weak) equivalence principle invalid? [closed]

As equivalence principle states Mass and weight are locally in identical ratio for all bodies. --Newton This implies that the gravitational mass does only depends on its inertial mass. Suppose ...
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### When do we use LQR controller and LQG controller?

I have to conceive a controller to my mechanical system to delete the problem of vibrations, but I don't know when we use LQR controller and LQG controller.
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### Can I disperse a droplet with electromagnetic fields?

If I have a droplet of water, can I apply an electromagnetic field in order to disperse the droplet into smaller subdroplets (tiny vapor) and fill a space with them? The same way that magnetic dust ...
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### Does there exist a free good molecule / atom simulation software?

I'm looking for a software or software package (for example C/C++) that can simulate a lot (say thousands at least) of molecules in action (ie. in movement or attached to say static walls). I have ...
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### What really is the significance of the resonant frequency in terms of “ease of vibration”?

I was studying the concept of resonant frequency and I've read quite a few articles and notes on it. What I have understood from what I have read is that the resonance frequency of an object is its ...
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### How does permanent magnets attract each other if the $B$-field can do no work? [duplicate]

How can two permanent magnets do work on each other? If you put two magnets with opposite poles facing each other they will attract each other. If you put them with the same poles facing each other ...
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### The Simulation Hypothesis As A Theory Of Everything [closed]

I have long found the Simulation Hypothesis to be better-able to answer questions that I have regarding the universe than the string theory and the quantum field theory. What I believe is that the ...
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### What is the total velocity/force on a particle in fluid?

I am now facing a fluid-particle interaction problem. I would like to simulate particle motion in a fluid. I do know the external force acting on a particle (dielectrophoretic force in this case) ...