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seen Feb 22 at 9:32

Jan
16
comment How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates?
Of course you've assumed here that the perihelion of the orbit is on the x axis. But then, the general case can be obtained just as easily by using the addition formula for $\cos(\phi-\phi_0)$.
Jan
15
awarded  Teacher
Jan
15
answered In the dual-slit experiment, can the time it takes for a photon to arrive reveal the path it took?
Jan
15
comment Why does kinetic energy increase quadratically, not linearly, with speed?
Your argument is wrong: When the machine is standing on the car and trying to accelerate the ball, it not only put a force on the ball, there's also the recoil force onto the machine. The machine is fixed on the car, therefore the recoil force slows the car. That is, the car loses kinetic energy. Where does that kinetic energy go to? Well, it goes to the ball!
Jan
15
awarded  Supporter
Jan
15
comment Why can't General Relativity be written in terms of physical variables?
Wouldn't the connection coefficients (Christoffel symbols) be the proper analog of the vector potential, rather than the metric tensor?