Scientists discovered that gases such as hot air and hydrogen float upwards. This led to the invention of airships and balloons.

Joseph and Etienne Montgolfier: inventors of the first hot air balloons

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In 1783, Joseph and Etienne Montgolfier designed and built the first balloon to carry a basket containing people into the air. The balloon was made with paper and cloth, and the air inside the balloon was heated by smoke from a fire on the ground below. The balloon was anchored to the ground with a rope, and stayed aloft for about 15 minutes.

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The first free manned flight (there were no ropes to hold it to the ground) was on 21November 1783. The balloon flew for about 25 minutes before landing.

The brothers had previously, in 1782, launched their first hot-air balloon. They used the smoke from a fire to fill a paper-lined silk bag with hot air. A basket was attached to the silk bag. As the hot smoky air filled the bag, the balloon rose into the air.

And earlier, in 1783, they made and launched another balloon that carried a sheep, a rooster and a duck. The balloon climbed to a height of about 1.8 kilometres and travelled more than 1.6 kilometres before landing safely. It was airborne for 8 minutes. Among the spectators to this historic event were King Louis XVI of France and his wife Marie Antoinette.

How modern balloons fly

Heat makes the air inside the balloon less dense than the air outside, so the balloon floats. Getty Images

Heat makes the air inside the balloon less dense than the air outside, so the balloon floats. Getty Images

Modern hot air balloons are made from lightweight, airtight and fireproof synthetic fabric. The air inside the balloon is heated by burning gas, which is stored in tanks inside the basket. The burners which are attached to the basket, heat the air to about 100º C. The hot air makes the balloon go up. To make the balloon go down, the pilot opens the vents on the top of the balloon to slowly release the warm air. The direction of flight is controlled by the wind.

Why do they fly?

There is air inside a hot air balloon and air outside of the balloon. When the air inside the balloon is heated, the atoms in the air move faster than the atoms in the air outside the balloon. This creates energy called kinetic energy. This means there can be fewer atoms inside the balloon so the hot air becomes less dense than the air outside. The heated air causes the balloon to rise. When the air cools, or is let out, the balloon goes down.

Watch a video about how hot-air balloons fly

http://science.howstuffworks.com/transport/43-how-hot-air-balloons-work-video.htm

Airships

he first airship, fitted with a steam engine was flown by Henri Giffard from Paris in 1852. The airship could only fly forward

he first airship, fitted with a steam engine was flown by Henri Giffard from Paris in 1852. The airship could only fly forward

Airships were built from 1884 onwards to carry cargo and people. They were fitted with engines, a propeller and a rudder for steering. The most famous airships were called Zeppelins after their inventor Ferdinand von Zeppelin.

The first zeppelins had rigid aluminum frames covered with fabric inside which were several gas-filled bags. The crew were in the gondola under the nose.

The Hindenburg: the largest airship ever built

When the Hindenburg exploded, 37 people died.

When the Hindenburg exploded, 37 people died.

In 1936 the largest airship ever built, the Hindenburg, was used to carry passengers across the Atlantic Ocean. It was 270 metres long and could carry one hundred passengers. In 1937 the Hindenburg caught fire when the flammable hydrogen gases used to lift the airship exploded as it was docking in the United States. 37 people died in the accident.

Modern airships are filled with helium gas which does not explode. They are smaller and are used mainly for advertising or to carry cameras for aerial photography. They are sometimes called 'blimps'.

Read a short history of ballooning

http://www.pbs.org/wgbh/nova/space/short-history-of-ballooning.html

Watch a historic video of the Hindenburg disaster