Let the position of your vagina in R-cubed be a function of time, v(t), and the position of my penis in R-cubed be a function of timed, p(t). Now let v(t)=(c1,c2,c3+Sin(f(t))) and p(t)=(c1,c2,c3+Cos(f(t)), where c1, c2 and c3 are constants determined by the location of the sex act, and f(t) is a continuous map that describes the intensity of our sex as a function of time.
Note that our synchronized orgasm occurs when f'(t) = 0.