The card will likely be reprogrammable using NFC to 'become' whichever card you choose.
Several large banks have had this in the works for a while, but it seems like Google will beat them to it.
In the simple case of just two metronomes on a single moving plane, the tendency for sync is governed by a non linear differential equation. The math gets rather complicated:
http://salt.uaa.alaska.edu/dept/metro.pdf