matthen:

Surprisingly such a simple system as a mass on a spring can exhibit very curious behaviour.  There are two motions interacting here, the side to side swing of a pendulum, and the up and down bounce of a spring.  If the bouncing is set to be twice as fast as the swinging then the system will swap between the two motions, regularly transferring up-down energy into swinging and vice versa. [video] [more] [code]

Interesting and informative. I mean, interestingly educational… wait, also, capturing; before I rebloged this post, I starred at this bouncing ball for like 15 minutes.