Last week's Dr Who episode "Kill the Moon" infected me with stupid, and now I am compelled to try to calculate the speed at which the dragon wags it's tail. Observational data: 1) Earth's moon had grown to have Earth gravity at this point, so I am assuming that it was also the size of the Earth when it turned into a puff cloud and vanished. 2) The dragon took about 1 second to flap it's tail half the distance that appears to be equal to the diameter of the Earth. Looking up the size of Earth, I get (13000/2)/1= 6500 kps. Obviously I've never tried anything quite like this before, how badly did I do?