In the original Karate Kid movie, the kid who wants to learn karate is frustrated by his teacher’s insistence that he spend his time painting fences and waxing cars. Only later is it revealed that the student had learned the fundamental moves without realizing it, blocking punches with “wax on, wax off.” Similarly, the deepest mysteries of physics are taught in Physics 101, but they’re hard to recognize in everyday objects like bicycle wheels and spinning tops.

One of these deep principles is the conservation of angular momentum. Angular momentum is the amount of rotation an object has, taking into account its mass and size, and it is curiously constant. A spinning figure skater has a constant angular momentum as she contracts her arms and twirls faster because a fast-spinning small object has as much angular momentum as a slow-spinning large object. A cloud of interstellar dust, stately drifting in…