CoachAll matter is made of molecules: unimaginably small particles, far below what any eye or school microscope can see. A single drop of water holds more molecules than there are drops of water in all the seas. Each pure substance is built of its own kind of molecule — water of water-molecules, iron of iron’s own particles — and a substance’s molecules are all identical.
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Example 45.4 (Six years of rules, one explanation)
Run the old rules through the model. Solids keep their shape: every molecule holds its post. Liquids take the container’s shape and lie level: the sliding crowd slumps until no molecule can slide lower. Gases fill all the room offered: nothing holds the flyers back. The perfume crossing the room: gas molecules flying, colliding, spreading. Sand pouring like a liquid: not molecules sliding, but grains — each grain itself a tiny orderly solid of trillions of molecules.
Example 45.7 (Squeezed air at work)
The bicycle pump squeezes room-fulls of air into the tire — possible only because air is mostly emptiness. The squeezed crowd, molecules hammering the tire walls faster and thicker, holds the bicycle up: a gas’s push is its molecular hailstorm. Divers’ tanks pack an afternoon of breathing into a steel bottle; the incompressible brake fluid, meanwhile, carries your foot’s push to the wheels undiminished — each state hired for its own talent.
Example 45.8 (The doors, molecule by molecule)
Warm a solid and its trembling molecules shake harder; at the melting point the shaking bursts the orderly stack — the crowd begins to slide: melting. Warm the liquid further and the fastest molecules tear free of the crowd’s grip entirely and fly: evaporation — and at the boiling point the escape becomes a stampede from within the liquid itself. Cooling runs the film backward: flyers caught (condensation), sliders locking into ranks (solidification). The six doors of last year are one story of molecular grip against molecular shaking.