Hot Air Balloons do!  See lots of them at Plano's Balloon Festival September 21-23, 2007.  Signs posted by Sci-Tech Discovery Center at the festival will provide explanations for the science behind hot air balloons.

Heating the air inside a balloon makes it less dense than the outside air, allowing it to lift off. A balloon stays afloat in air, like a boat in water, because its volume, shape and lighter air provide an upward force, or buoyancy. 

Air is always moving even though it might not seem windy.  Air molecules move at over 1,000 miles per hour.

The sun’s light scatters as it shines through the atmosphere.  Blue light scatters more than other colors because of its shorter wavelength.  Why don’t we see violet since it is the shortest in the visible spectrum?  Our brains interpret blue better.

Pilots fly balloons in the morning or evening because the air is more stable.  Heat absorbed during the day by things on Earth can cause unstable wind in the middle of the day.

Propane burners heat the air inside a balloon to make it lighter than the outside air.  A typical hot air balloon holds 65,000 cubic feet of air heated to about 212° F.

Hot air balloons don’t have steering wheels.  Instead, pilots either release hot air to descend - or heat more air to climb - to a wind current blowing in the direction and speed they prefer.