The Lagrangian of a free particle. (mv²/2)
Hello everyone, I've been having trouble with the following reasoning for a while. The book I use for learning is Landau and Lifschitz vol1. When the concept of the Lagrangian is introduced in...
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Pressure Drop Testing - Too Many Unknowns?
Hello there, I am having a discussion with a co-worker about a pressure drop test. I have two different 'boxes' for which I don't know the pressure drop. What I want to know is the difference in...
View ArticleLorentz force law from action
Hi, I am trying to derive the Lorentz force law in the following form: [tex] q \frac{dw^\mu}{d\tau} = q w^\mu \partial_\nu A_\sigma \epsilon_\mu^{\nu \sigma} [/tex] by varying the following Lagrangian...
View ArticleAdditive Pair Potential
I'm sorry, I wasn't exactly sure where to put this question but this section is probably my best bet. I'm basically trying to understand potential functions of more than 1 parameter... which is...
View ArticleAcceleration in conservation of momentum problem
If a moving point mass collides with a point mass at rest then you can find the resulting velocities by conservation of momentum and conservation of kinetic energy. Are the accelerations in this case...
View ArticlePoynting Vector and Mobile phones in ovens
Hi, sorry if this is in the wrong forum but 2 Quick hopefully simple questions about Poynting vector and EM waves. Q1) Say I have two antenna (antenni?)...dipoles maybe, both with say, 50W going into...
View ArticleExpansion of a local dissipation function
Hello everyone, I'm studying the finite strain theory and have come across the maximum dissipation principle. It implies a dissipation function defined as [itex]D=\tau:d-\dfrac{d\Psi}{dt}[/itex][itex]...
View ArticleA question about equations of motion under constant acceleration
This is a very basic question. We know for a particle moving under constant acceleration we can use both the equations [tex] x = \frac{v + v_0}{2}t [/tex] and [tex] x = v_0t + \frac{1}{2}at^2 [/tex]If...
View Article(Eulerian) Velocity of an elementary vector
Hello everyone, In order to define the eulerian rate deformation tensor, one should first express [itex]\dfrac{d}{dt}(\underline{dx})[/itex] in gradient velocity terms (denoted [itex]\underline{\nabla...
View ArticleFinding the electric and magnetic fields from a scalar potential?
E = - grad*phi - 1/c (dA/dt). phi is the scalar potential, and is given. How do I calculate the vector potential = A ? Is it A = (v/c) * phi ? If it is, then where is this equation coming from? Thank...
View ArticleDoes slimy spit have a spring constant?
Hello WARNING: Some people may find this post a little gross. I observed something today that I didn't know could happen in fluids, only in solids. I let some slimy spit out from my mouth. It became a...
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Vibrating sphere: pressure
Hi, Attached is the equation relating the vibration of a sphere radius R, to the pressure field it generates. ρ is the density of the medium in which the sphere sits. The article I got this from just...
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A question about conservation of momentum (Lagrangian)
The image seems to be not showing here is the link : http://imgur.com/QhYG54l What does Landau mean here by the Lagrangian remaining ''unchanged''. Is it the value of the lagrangian as a function that...
View Articleexperiment - pepper and soap
Hello. I have a question... I think that you know the experiment with pepper and soap. (you put water on plate, than you put a lot of pepper on in, than you put on your finger some soap and than you...
View Articledensity of liquid
Please, tell me really simply from the viewpoint of molecular physics... Why is liquid having a smaller density on liquid having a bigger density? Thanks
View ArticleWhy incompressible fluid flow is advantageous in numerical computation
Hi, When we want to solve the Navier-Stokes equations coupled with the conservation of mass for incompressible fluids using the primitive-variable approach, we have to face to the problem that the...
View ArticleAbout voltage and capacitance
Hi everybody, I'm new at the forum. I've started learning physics on my school last year. I've a question. How can we measure the voltage stated on the definition of capacitance? Just V=Q/C ? Or how to...
View ArticleA layman's question about Thermodynamics (End of the universe)
I am little experience of physics so please be patience with me, This is my first post of this great internet forum. I have a friend who said that energy will never remove from the universe only...
View ArticlePressure vessel ideal gas calculation
Hello all, As part of a research project, I am trying to calculate the amount of water/dry ice I would need to put in a cylindrical pressure vessel to obtain an internal pressure of ~100 psi at 200C...
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