Recent content by alex4lp

Sorry if I came back here, but I still have a little doubt: what we can say about Kerr black-hole? The space-time it's only axisymmetric and so is there any method to demonstrate that matter would collapse in the singularity (i'm always considering the destiny of the mass that generates the...

Ok perfect, thank you everybody!

Ok, but the model is true only in an exterior region of the mass. How can i give prediction inside the mass? The singularity is inside the sphere...

Ok, but "mathematically" speaking, how can i say it? Which equation tells me "the mass has to fall down to the singularity?" if I can't use the Schwarzschild metric inside the mass itself? Is it a supposition?

Hi everybody, and thanks in advance. My doubt is: why should the mass go in the singularity? I'm thinking about this situation: imagine a sphere with radius R<2M; then that sphere generates a BH. Schwarzschild tensor metric is valid only in the exterior region of the mass and for this reason i...

Perfect, that's exactly what i needed! Thank you very much!

Good morning everybody. I have a problem with this wikipedia passage https://en.wikipedia.org/wiki/Schwarzschild_geodesics#Bending_of_light_by_gravity 'cause it says "Expanding in powers of rs/r, the leading order term in this formula gives the approximate angular deflection δφ for a massless...

Perfect, thank you!

I know that d/dt (x) = 0 ⇔ x = constant (of time), it's obvious. I can't understand why we have a constant (v1) when i don't see the equation ∑ F = 0 or ∑ = r x F = 0. This v1 is the velocity of a mass (for example of water) through an entire volume of the tube and it's a constant of time, but...

In a stationary flow, d/dt (v1) = 0, where v1 is the fluid velocity through the volume V1. I can't understand why, because we have 2 kinds of forces acting on our mass, and i can't find the equation Σ F = 0.

Yes, but my problem is that in the section A1, v1 is constant. I know that v1 ≠ v2, but in their regions (A1*v1*Δt and A2*v2*Δt) they are constants, with v1 ≠ v2.

We are measuring the volume V = S * v * Δt, so v is a constant, infact we are talking about a stationary fluid flow.

https://www.google.it/search?q=continuity+equation+fluids&espv=2&biw=1745&bih=868&tbm=isch&imgil=FCuXtyxr0h586M%253A%253B7URLq9gFwAu_4M%253Bhttp%25253A%25252F%25252Ffree-stock-illustration.com%25252Fcontinuity%2525252Bequation%2525252Bfluids&source=iu&pf=m&fir=FCuXtyxr0h586M%253A%252C7URLq9gFwAu_...

Sorry, you're right. I'm considering the equation 1/2 ρv^2 + ρgz + P = constant. I'm wondering why that "v" in the equation is a constant (in the related section S) if this equation is obtained considering pressure forces and gravity force ≠ 0. for example here...

Hi everyone and thank you in advance. My first problem is: if v1=constan in a section S1, it should not be ∑ F = 0 ? Or maybe Σ M = 0 ? Because all forces that i recognize are gravity and pressure, but i never found the equation mg - PS = 0 or something similar. I was thinking about something...