= Resistive magnetic entry of a falling loop
{title2=$\tau=mR/(Ba)^2$}
A rectangular loop entering a uniform <magnetic field> while only one horizontal segment is immersed has <motional electromotive force> $Bav$. Neglecting <self-inductance>, its <electric current> is $Bav/R$ and its upward <magnetic force> is $(Ba)^2v/R$. The equation $m\dot v=mg-(Ba)^2v/R$ gives exponential relaxation toward $mgR/(Ba)^2$. This entry model ends when both horizontal segments enter the field; then their net magnetic force and the rate of change of external <magnetic flux> vanish.
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