gas tank, plastic, wood
It can be, but usually not. Helium is a bit expensive, and it'd cost too much for most balloonists to use it. It's cheaper to use a hot air balloon. helium is lighter than air. hence balloons filled will helium will float in air.
There are traditional hot air balloons, special-shaped hot air balloons (such as animals, objects, or characters), and solar-powered hot air balloons that use solar energy to heat the air inside.
Hot air balloons typically use propane gas as a fuel source for the burner that heats the air inside the balloon envelope. The propane is burned to heat the air, which causes the balloon to rise.
'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 air. A craft that can be in the air is usually used (couldn't use a ship eh?) such as an aeroplane or helicopter. During the first world war airships and reconnaissance balloons were used. Weather balloons and satellites can be used nowadays.
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.
Yes
Yes
The first use of hot air balloons was in the American Civil War for surveillance of troop movements.
Helium gas is commonly used to fly balloons due to its lighter-than-air properties. It is non-flammable and safe for use in balloons to provide the lift needed for them to float in the air.
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You may use airplanes or balloons (aeronautics).