CoachAir is the invisible stuff all around us. It has no color, no smell of its own, and light passes straight through it — which is why we forget it is there. But it is real stuff, as the experiments of this chapter will prove, and it is precious: every breath you take is a gulp of it.
Examples
Example 10.2 (Try it: catch some air)
Open a plastic bag wide, sweep it through the room, and twist it shut. The bag stands puffed up like a cushion — squeeze it: it pushes back! Something is clearly trapped inside. Open a corner and squeeze again: you feel the invisible prisoner stream out over your fingers. An “empty” bag full of nothing could not push back.
Example 10.3 (Where air shows itself)
Air is invisible, but its tricks are not: it wobbles as shimmering above a hot road, it lifts kites, it rustles the leaves, and it makes bubbles wherever it escapes underwater. Blow through a straw into your glass: every silver bubble is a little parcel of air on its way up.
Example 10.5 (The glugging bottle)
Push an “empty” bottle mouth-down into the basin and tip it slightly: glug, glug, glug — big silver bubbles race to the surface, and water takes their place inside. The bottle was full of air; the water can only move in as fast as the air moves out. That glug at the kitchen sink is the sound of air and water swapping rooms.