yes they use altimeters and gps's
Hot air is used for hot air balloons.
Hot air balloons use the fact that hot air rises as a way to make balloons fly. When the air inside the balloon is heated, it rises, and this creates lift which is used to make the balloon fly.
Fire and, well, hot air.
'Hot air' balloons don't use hydrogen. They use hot air. Balloons that use hydrogen are not referred to as 'hot air' balloons. The only balloons that can accurately be referred to as 'hot air' balloons are the members of the balloon population that derive their lift/buoyancy from the presence of hot air. Of course, if a balloon used no hot air, then it could freely be referred to as a 'hydrogen' balloon, a 'helium' balloon, a 'water' balloon, etc., depending in congruent harmony with the nature of whatever substance had been chosen with which to inflate it it in order to maintain its fulsome shape.
The first use of hot air balloons was in the American Civil War for surveillance of troop movements.
Yes
Yes
hot-air balloons and birds in flight.
bbksu
Hot air balloons use hot air. They have a burner to heat the air. Hydrogen balloons were too dangerous because hydrogen is highly flammable, even static electricity could cause an explosion. Helium is safer because helium is not flammable.
Hot air balloon pilots use propane to heat their balloons. It's inexpensive, very easy to obtain, and works.
Balloons can be filled with air (don't float), or with hydrogen or helium (float because the gas is less dense). Hot air balloons use burners to heat the air so that it becomes slightly less dense than the cooler air around it, providing some lift.