Early flying machines were lifted high into the air by buoyancy. Much like a fish floats in water these giant craft floated in air. On June 1783 the Montgolfier brothers were the first to create a hot air balloon that carried people some 9 km over Paris.

Commercial flights soon began with the advent of giant airships filled with hydrogen gas. Hydrogen is lighter than air but is extremely flammable. The later property of hydrogen proved to be a significant set back to early commercial travel.

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1) What is buoyancy?

2) Explain how buoyancy is generated in a hot air balloon

3) Explain how the flying vehicles shown here rise into the air. In your explanation use the following words.
buoyancy, gravity, density