Hot air balloon
Hot air balloons work by heating the air inside the balloon, usually with a fire of some kind. Hot air weighs less than the same volume of cold air (it is less dense), which means that hot air will rise up or float when there is cold air around it, just like a bubble of air in a pot of water. The bigger the difference between the hot and the cold, the bigger the difference in density, and the stronger the balloon will pull up. This means that balloons can carry more weight on a cold day, or if the air inside the balloon is made very hot.
Hot air balloons construction has many different factors:
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