Dear Brothers Magliozzi, Speculating over a recent listener letter postulating a slowdown of the earth's rate of rotation due to the hypothetical billboard-induced aerodynamic drag, you were heard to wonder what causes the earth to spin in the first place.
Nothing currently causes the earth to spin.
True, something or someone must have set the planet spinning at the start of its existence, but these days it just keeps on spinning simply out of inertia, the same phenomenon Isaac Newton spent many of his days dreaming about and, more relevantly, the same phenomenon that causes Tom to be unable to rise from the couch he slept on most mornings. But the ultimate cause of all wind must be assigned to the sun, whose blessed rays provide thermal energy to the air, enabling it to move around. In fact, the sun, through the miracle of photosynthesis and all the vegetable and animal life sustained thereby, makes possible that other kind of wind which no doubt emanates from the posterior regions of certain public radio personalities after dining at a certain restaurant known as The Tasty. Such is the wonder of universe. Here's some of the good stuff that's come in recently.