How Things Work Chiildcraft Volume 7 Author:How & Why Library There's more to a door than you think. — Pipes you see, pipes you don't. — It's heat. — Clocks & watches. — Things that make sounds. — Things that make music. — Mirrors, lenses and prisms. — Things that help us extend our reach. — Batteries, cells and generators. — Plugs, sockets and switches. — Saws, hammers and other tools. — Machines that make work easi... more »er.