Recent content by adphysics

I know. I'm just having trouble understanding how, say, the Lorenz gauge is actually related to the simultaneous gauge transforms shown above. In all the derivations I've encountered of the wave equations for E and B using the Lorenz gauge, like this one...

Sorry, I should have been more clear. That part I understand. I understand why, if we begin with E=-grad(phi)-dA/dt and make the simultaneous gauge transforms, we have the same electric field. What I don't understand is the following: Take the divergence of the electric field: div...

I understand the concept of a gauge transform, and I understand why it is that the magnetic field would be unchanged with the addition of the gradient of an arbitrary scalar potential onto the magnetic vector potential A, and I understand why the electric field E would be invariant under the...

Oh, yeah. The engine is on the back of the rocket, so it accelerates with the rocket, so if an engine ejects exhaust at a velocity v, then this is what is observed from the rocket's point of view. Now I feel somewhat embarrassed, but at least the rocket equation makes sense now.

Oops. So assuming a constant mass flow rate the propellant exerts a constant force on the rocket so the rocket's acceleration increases as follows: a(t)=F[1/m(t)] where F is a constant (until fuel runs out) where m(t) is the mass of the rocket at time t. m(t)=m(initial)-bt where b is a...

In deriving the rocket equation, there is one part I don't understand. The velocity of exhaust with respect to the body is assumed to be constant, where: v(exhaust wrt body)=v(exhaust wrt inertial)-v(body wrt inertial) So assuming a constant mass flow rate, the rocket propellant exerts a...