<p>Computer scientists, as a lot, tend to have a pocket industry of proving that this or another toy model is equivalent to Turing machines. Billiard balls can be used to implement the Fredikin gate, which is universal for computation, and thus you can program your local pool table. Magic: the Gathering is infamously Turing complete, a fun fact to bring up during draft.</p><p>Those kinds of proofs are useful because the easiest way to show something can be programmed is to do it.</p>