your voice on tape and which also operates as a loudspeaker; a one-way balloon valve; a metal detector; a box with a combination lock; a burglar

alarm; an electric motor; a simple computer; musical instruments that play in tune; and a kite that flies.

There are also working models that you can build to understand the principles that make things work. These include a model escalator with steps that move;

a model autopilot that can sense its direction of movement; a bar-code reader that reads codes in the same way as a real one; a model aqualung that supplies air in the same way as a real aqualung

used by divers to breathe underwater; a

model rocket that takes off; and a model disk drive that stores information like the disk drive in a computer.

These are only a few of the many

experiments in this book. Some are simple enough for you to do on your own, while

others are more complex and may require help. Carry

them out carefully and you

will find out about all kinds

of things that you use or see

every day-from cars to

computers, from toasters to

television, and from simple levers

to mighty skyscrapers.  0  0