Yes, this is why the concept of energy is given such a prominent position in physics. It is a great tool for predicting what might happen even when the detailed

Yes, this is why the concept of energy is given such a prominent position in physics. It is a great tool for predicting what might happen even when the detailed mechanism is unknown or seemingly impossible. I haven't yet taken the time to understand the details of these explanations, but when I heard about this cart I immediately thought "hmm, the wind is blowing, there's energy all around, so some tricky person can probably figure out how to make use of that energy; hence, it's plausible". Of course, the flip side of this principle is that physicists can be driven to spend years and years and years trying to extract energy that is obviously there, but that has no known mechanism for getting it out. The classic example is nuclear fusion. Everybody knows it's energetically favorable; nobody knows how to get over or under the activation barrier in any useful way, other than "build something the size of a star".