00:00On the 19th of September 1783 a large crowd gathered in anticipation at the
00:11Palace of Versailles in France. Tens of thousands of people including King Louis
00:17the 16th and Queen Marie Antoinette were about to witness a duck, a rooster and a
00:23sheep named Montauciel take flight in a hot-air balloon. The balloon was invented
00:29by French brothers Joseph Michel and Jacques-Étienne Montgolfier. Their
00:35interest in ballooning followed experiments on smaller paper or fabric
00:39bags filled with hot air. Having successfully launched an unmanned hot
00:45air balloon in June 1783 a demonstration in front of the King was planned for
00:51September. Concerned about the safety of balloon flight the King suggested using
00:55two condemned criminals. The Montgolfiers instead suspended three unsuspecting
01:01animals in a round wicker basket beneath the balloon which was fashioned out of
01:06cotton canvas and paper. The balloon flight was successful soaring 600 meters
01:13into the heavens before slowly descending eight minutes later and
01:16landing 3.2 kilometers away. The duck, rooster and sheep lived to tell the tale.
01:22They were the first living beings to fly in a hot-air balloon. Successful human
01:29flights were completed later that year. Meanwhile the Montgolfiers despite
01:34inventing the hot-air balloon couldn't explain why it floated. Joseph Michel
01:41mistakenly believed he had discovered a new gas the Montgolfier gas which was
01:45lighter than air and released from burning embers. We now know the real
01:51reason hot air balloons float and it's nothing to do with an imaginary gas. Hot
01:57air balloons simply obey certain laws of physics or more precisely the air
02:02particles within hot air balloons and elsewhere in the atmosphere obey the gas
02:07laws. The gas laws tell us how the temperature, volume, pressure and amount
02:13of gas are all related. The gas laws were discovered using scientific experiments
02:19sometimes though not always with the help of balloons. Of course observing and
02:25experimenting on the world around us is common practice now but it was a
02:29controversial idea when Robert Boyle was born in Ireland in 1627 the 14th child
02:36of the very wealthy first Earl of Cork. Ideas based on reasoning were more
02:42likely to be accepted than ideas tested in experiments. Boyle disagreed with this
02:47and his vast inherited wealth allowed him to spend his life studying science
02:51and promoting the experimental method. In one of his most famous experiments a
02:57J-shaped tube was built by his assistant Robert Hooke with mercury poured into
03:03one end. At the other end of the tube a pocket of air was contained. As mercury
03:09filled the tube it exerted increased pressure on the air pocket and this
03:14reduced its volume. All else remaining equal if you squash a certain amount of
03:20gas into half its previous volume you will double the pressure that gas exerts
03:26on its container. Boyle wasn't the first to test these ideas but he was the first
03:31to publish his findings now known as Boyle's law. You can feel the effect of
03:37Boyle's law whenever you squeeze a bike tyre or squash a balloon. This makes
03:42sense when we consider that gases are entirely made up of many smaller
03:46particles, atoms or molecules constantly whizzing around. By forcing the same
03:52amount of gas into a smaller volume you can feel a higher concentration of
03:56particles bumping against or exerting pressure on the surface of the container.
04:01How fast or slow these particles move meanwhile depends on their temperature.
04:07In fact that's essentially how temperature is defined. Boyle's law
04:11assumes that the amount of gas and the temperature of that gas are kept
04:15constant. It would be more than a hundred years before the next gas law was
04:20defined, one that considers the relationship between gas volume and
04:24temperature. During the 1780s as the Montgolfiers were launching hot air
04:30balloons with the help of their fantasy Montgolfier gas, a genuine lighter than
04:35air gas was also being tested for balloon flight. On the 1st of December
04:401783, 10 days after the first manned hot air balloon flight, fellow inventor Jacques
04:46Charles launched the first manned hydrogen balloon flight. Hydrogen is less
04:51dense compared to the elements that make up the atmosphere. But what if it were
04:56also heated? Would it become even lighter? Four years after the pioneering balloon
05:02flights of 1783, Charles filled five smaller balloons each to the same volume
05:08but with a different gas. He then heated every balloon to 80 degrees Celsius and
05:13saw that they all expanded by the same amount. Although he failed to publish
05:19these findings at the time, they were later credited to him by natural
05:23philosopher Joseph Louis Gay-Lussac. Charles' law now famously describes how the
05:30volume of a sample of dry gas is directly proportional to temperature, all
05:34else being equal such as air pressure and gas amount. As well as hot air balloon
05:40flight, Charles' law can explain rising thermals of air in the atmosphere. When
05:45the Sun heats the Earth's surface it acts as a radiator and warms the air
05:49immediately above. That air expands as it warms and its lower density compels it
05:55upwards. We see this all the time. On a small scale, rising air gives us fair
05:59weather clouds, showers and thunderstorms. On a larger scale, rising air results in
06:05tropical cyclones, low pressure, weather fronts and global wind circulation. The
06:11engine that drives hot air balloons is ultimately the same engine that drives
06:15all of the planet's weather, rising bubbles of hot air governed by Charles' law.
06:20Of course the atmosphere is chaotic and complicated. As well as Boyle's law and
06:25Charles' law, there are other gas laws that help explain the relationships
06:29between air pressure and temperature, as well as the amount and volume of gas.
06:34These gas laws will be explored in part two, along with the ideal gas law, which
06:40unites all of the various relationships in one equation and is essential for
06:45predicting the weather.
06:50you
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