So simple, and yet so chaotic:
The above image describes the path of a Double Pendulum: two rigid rods with weights at one end, attached end-to-end. (I couldn't find the source of this animation, if you know who made it please let me know in the comments.) Given enough of a push, the path of the pendulum is chaotic and impossible to predict. The slightest change in the initial position of the pendulum or the forces on it (from the push, the atmosphere, or friction from the bearings) will completely change its path in the long term. The animation (being pre-rendered) is deterministic, but here's a long-exposure trace on a real-world double-pendulum (via Wikipedia).
While double pendulums are hard to predict in the long-term, it is possible to predict their short-term behaviour, as this robot balancing a triple pendulum demonstrates. Perhaps one day this technology will be put to practical use, like this:
Yes, the ad is fake, but the application isn't infeasible! That's all for this week, enjoy your weekend and we'll be back on Monday.