How do balloons work?

Hot air rises. The envelope traps a large
bubble of hot air. If the air in the envelope
is heated by a burner, the balloon will rise.
If the air in the envelope is allowed to
cool or if the hot air is "vented" (allowed
to escape) from the top or the side of
the envelope, the balloon will descend. An
altimeter (to measure altitude), a rate-of-climb
meter, and an envelope temperature
gauge are the only instruments used in the
balloon. Amazingly, the pilot can control the
altitude of the balloon within a matter of inches!

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