CoachWind is air on the move. Still air brushes nobody; moving air pushes whatever stands in its way — gently on a breezy day, hard enough in a storm to bend trees.
示例
Example 10.8 (Air at work)
Moving air does real jobs: it fills the sails of boats, spins wind toys, dries the laundry, and carries kites. You make wind yourself every time you blow out a birthday candle — your breath is a small private gust, strong enough to push the flame right off its wick.
Example 10.9 (Try it: the balloon jet)
Blow up a balloon and hold its neck shut. Inside, squeezed air is waiting. Let go: the air rushes out backward, and the balloon shoots forward across the room, wobbling wildly. The escaping air pushes the balloon — a tiny cousin of the way squeezed-out gas pushes real rockets.