2. Hot-Air Balloons hot-air balloon – a large balloon that rises with the aid of hot air

3. Hot-Air Balloons The first hot-air balloon was designed and built in 1783 by the Montgolfier Brothers in Paris, Francis. In 1870, with the Prussian Army surrounding Paris, the French smuggled people and messages out of the city using hot-air balloons.

4. Hot-Air Balloons: How They Work hot air is less dense than cold air – density is the mass of an object divided by the volume of the object – heat speeds up the motion of the air particles so that fewer particles of hot air occupy the same amount of space – with fewer particles, the hot air has less mass, and is therefore lighter than an equal amount of colder air the hot air balloon itself is heavier than the air, however, the hot air within the balloon is less dense than the colder air around them, so the air within the balloon lifts the balloon and basket off the ground

5. Other Gases Used in Balloons balloons can also use hydrogen and helium to float – because hydrogen and helium are lighter than air and will float airships – gas filled balloons with a motor and propeller

6. Airships large, cigar-shaped airships, known as zeppelins, were commonly used during WWI they used hydrogen, which is highly combustible, in the balloon

7. Airships Not always a good idea!

8. Airships Nowadays, airships use helium, which is much safer.

9. The Breitling Orbiter 3 In 1999, Dr. Bertrand Piccard and Brian Jones were the first to fly a hot-air balloon around the world non-stop. It took only 3 weeks.