# Recent content by SergejVictorov

Thank you!
2. ### Invariance of scalar products on Lie algebras

Hi folks, If I have a Lie algebra \mathfrak{g} with an invariant (under the adjoint action ad of the Lie algebra) scalar product, what are the conditions that this scalar product is also invariant under the adjoint action Ad of the group? For instance, the Killing form is invariant under...
3. ### Chern Simons form: calculation

Hey folks, I'm trying to understand a couple of calculations in Chern-Simons theory and I'm stuck. I want to prove the following in four spacetime dimensions: Let G be a Lie Group with generators T_{a}. Further let A=T_{a} A^{a}_{\mu} dx^{\mu} be a connection and F=dA+A \wedge A its...
4. ### Phi 3 scalar field theory

You don't have to guess here. I will just cover the phi cubed case. Are you allowed to use Feynman's rules? If yes, just draw the 2+3 external lines and two vertices with three outgoing lines each and draw all topologically distinct diagrams. After that, you can write down the terms very easily...
5. ### Needing help with projectile trajectories

You need to set up the differential equation of motion in two dimensions. In a simple model there are only two forces involved: gravity, which is constant and air resistance, which is proportional to velocity squared. There is no analytical solution, therefore you have to integrate the equations...
6. ### Fluid model question

I have a specific question about fluid analysis that is bugging me. I am no expert in this field but very interested in it. Lets's say we want to model a flow where air expands out of an air reservoir across a valve into a cylinder and applies a pressure force on an airtight piston, which...
7. ### Introducing LaTeX Math Typesetting

\lim_{\substack{x\rightarrow 0\\}} f(x,y)
8. ### Find the distance/height, impact ,etc of the tsunami?

Perhaps you are looking for something like this: http://mathworld.wolfram.com/news/2005-01-14/tsunamis/
9. ### Drag Equation Derivation:

All I wanted to show is that there is a way to come up with the drag formula, nothing more. Perhaps someone knows the true origin, if I didn't capture it. This formula works amazingly well for what it's intended, and it's used quite often for simple models on a level where students don't know...
10. ### Drag Equation Derivation:

Okay, I'll do the derivation in terms of energy because it's easier than with momentum and doesn't even involve calculus. Let's start with the kinetic energy of the fluid in front of the body: E=\frac{1}{2}m v^2 The mass is given by the area times an arbitrary length times the density...
11. ### Drag Equation Derivation:

Actually, there is a derivation for the drag formula. You have to write down the momentum contained in a fluid element and differentiate with respect to time, after which you integrate over dV. This will give you the formula without the drag coefficient, which is plugged into the formula...
12. ### Rail Gun physics, need assistance

Recoil does not depend on the mechanism used to accelerate the projectile. Whenever you accelerate something, there is a force in the direction of acceleration. This is the force the gun exterts on the projectile. There is an equal and opposite force acting on the gun, which accelerates the...
13. ### Fighter aircrafts have the jet engines buried inside the fuselage

The moment of inertia along the longitudinal axis is also kept small by placing the engine inside the fuselage, increasing maneuverability. Another benefit would be lower air resistance.
14. ### How much money is sufficient for you?

Foreigners are usually treated good. There are some folks who are prejudiced when it comes to foreigners but I believe they are the minority. Italian, Portuguese and Spanish people have established a good presence in Switzerland. After all, 21.6% of the Swiss inhabitants are foreigners. I've...
15. ### How much money is sufficient for you?

Well, I must say I can't complain about life over here. For young people, finding a good job without degree can be difficult. Also, living costs are said to be very high. You can have a hard time finding a nice apartment with 4 rooms for less than 1200\$ a month. Decent restaurants are also...