Friction on a rotating disc
If I have a spinning circular disc of uniform density, how would I find the torque generated by friction, if the disc is lying flat against a table with coefficient of friction μ? τ=Fxr, but what is F,...
View ArticleDeriving the curl of the magnetic field
So i was wondering how the curl of the magnetic field is derived since Feynman just introduces it from nothing in his second volume of Feynman's lectures on physics: c2∇xB=j/ε0 or the other one where...
View ArticleWhich scatters light more: a sphere or a hemisphere?
In case the context, which this question is based needs to be provided, the context follows. A sub-project was being done on using sphere or hemisphere "scatterers" on TFSC (Thin-Film Solar Cells)....
View Articleangular and linear velocity of a rigid body given a force.
Hello, I'm trying to prove a simulation of mine is working correctly. the simulation has a cube of sides 1, mass 1 and c.o.m. position at (0,0,0.5) ie sitting on the xy plane. i have a force along the...
View ArticleSystem mass-spring-damper and Energy
Hellow! A general system mass-damper-spring is describied by differential equation: [tex]m \frac{d^2x}{dt^2}+\gamma \frac{dx}{dt}+kx=F[/tex] For calculate the energy in this system just integrate the...
View ArticleConservation of Momentum in a Single Direction
The Law of Conservation of Momentum states that the total linear momentum does not change in any closed system not subject to external forces. However, is it true that the momentum in, say, the...
View ArticleIs spin angular momentum increasing in a gyroscope?
In my textbook there is an equation for the precession frequency: Ω = τ/Iω The derivation in the book shows no difference in the spin angular momentum at time t = 0 and t = delta t but when I tried it...
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E&M energy density near a radiating hi Q half-wave antenna.
A high Q antenna basically means the antenna stores a large amount of energy in the near fields compared with the electromagnetic energy radiated per cycle? When the alternating current momentarily...
View ArticleElectric field inside a charged sphere
If we have a uniformly charged spherical shell, supposing that the shell is non-conducting, could we have any electric field inside the sphere? Why?
View ArticleLens numerical aperture
Hi, I have a question about resolution as defined by rayleigh's equation r = 0.61 x lambda/numerical aperture The maximum half angle of acceptance of a lens is 90 degrees and the sine of this is 1. At...
View ArticleMore on Hall's Mercury precession
Hall showed that a slightly higher exponent in Newton's equation would cause precession. Would there be the same effect if the product of the Sun and Mercury's masses reduced slightly as Mercury...
View ArticleIntegral of magnetic field over the sphere
If all the currents were inside a sphere with the radius R, then we would have [itex]\int B \,dV= 2/3\mu_0 M[/itex] where [itex]M[/itex] is magnetic moment of all the currents and [itex]B[/itex] is...
View ArticleThe police car moves faster than the speed of sound? Sonic boom.
Hi, Suppose the police car moves faster than sound's speed and runs away from the person on the street. Will the person hear the siren? Regards,
View ArticleThe police car moves faster than the speed of sound?
Hi, Suppose the police car moves faster than sound's speed and runs away from the person on the street. Will the person hear the siren? Regards,
View Articlereturn current
hello I need to know about return current formation at beam plasma system, in a simple way. how It is formed?
View ArticleRolling on flat floor, rolling down an inclined plane?
When rolling on a flat floor when the velocity at the circumference equals the velocity at the centre of mass the friction stops acting right? SO why does't that happen when it is rolling down an...
View ArticleEquations of state = superfluous state variables?
I don't get the point of equations of state since they seem to me to just indicate that we defined too many state variables. Why not just trim down our set of state variables and do away with the...
View ArticleGenerally applicable development of classical perturbation theory
Greetings, Does anyone know of some good sources that explain classical perturbation theory, preferably using the Lagrangian formalism? The sources that I have seen more-or-less say, "write...
View ArticleNewton's 3rd Law and electric charges
Hi, Is Newton's 3rd law applicable to electric charges? I have a problem with a situation where two identical positive charges moving perpendicular to each other. The magnetic forces exerted by each...
View ArticleEscape velocity
I'm having trouble understanding the idea of escape velocity. How can an object escape the gravity of a massive object like the Earth? No matter what the velocity the object is, doesn't Newton's law of...
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