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"head" in the name refers to the Mathematica concept. That was the first account I created. I kept the name.


Sep
26
answered Ball Bearing Inside a Hollow, Spinning Rod: where is the logical flaw?
Sep
26
answered Harmonic oscillator differential equation solution
Sep
24
awarded  Autobiographer
Sep
18
answered Can a bullet really fly through space forever?
Sep
13
revised Inconsistency between Helmholtz and Gibbs Free Energies
fixed an equation
Sep
1
answered Electric Field and Calculus: What is the physical significance of infinitesimal $dA$ in the equation of Gauss's Theorem?
Aug
22
reviewed Leave Open Is light so important in special relativity?
Aug
22
reviewed Close Speed greater than light in circular motion
Aug
22
reviewed Leave Open How to calculate the intensity of the interference of two waves in a given point?
Aug
22
reviewed Leave Open Why doesn't the light from galaxies appear stretched?
Aug
13
revised How to understand Feynman's reasoning about perpetual motion?
added 255 characters in body
Aug
13
comment How to understand Feynman's reasoning about perpetual motion?
@Bardo Good question, I should have explained. You would have that extra lifted weight in the final state. Then you lower that weight and get the 'free' energy as you say. At this point you are back in the initial state, and you can repeat the procedure to lift the weight back up. So by repeating this process, you can get as much 'free' energy out of the system as you want. I have edited my answer to include this information.
Aug
11
comment Story about a mathematician, a dinner party, and the three-body problem
It sounds like you (Yoav) are talking specifically about lagrangian points. I haven't heard the story though.
Aug
11
reviewed Leave Open Distance along projectile motion
Aug
8
comment Does a 4-current J determine a unique maxwell-faraday F tensor up to isometry?
The idea of advanced and retarded solutions is important here too. You can imagine a current density that is a delta function in space time. Then when the current appears and disappears you have a sphere of em radiation going out at the speed of light. But then you can also time reverse this solution to see a sphere of radiation moving inward at negative time, until a current appears and disappears to kill the radiation at time zero.
Aug
6
comment Rotating platform with pulleys and stacked blocks
Since $A$ and $B$ are connected by a rope, one will start moving as soon as the other does. Thus they are both on the verge of slipping at the same time.
Aug
6
reviewed Close Mass term in the Lagrangian
Aug
1
comment Magnetic field above center of current-carrying loop
Hint to Hint: Consider the case $z=0$, i.e., $\alpha = 0$.
Jul
31
reviewed Close Airplane on a treadmill
Jul
31
reviewed Close Is the second law of thermodynamics a real law?