Why do hot air balloons rise? What principle to use

　　The basic principle is thermal expansion and contraction. After the air is heated, the specific gravity will become lighter and rise upwards, because air is a mass substance. The same volume of air has different temperatures, and their density and mass are also different. After the air in the balloon is heated, the density becomes smaller, and the mass is lighter than the cold air of the same volume outside the balloon. Therefore, the balloon generates buoyancy and takes off. For aircraft, this buoyancy is called lift. When the burner heats the air in the balloon, the air in the balloon expands and the density becomes smaller. After the expansion, the excess air is discharged from the bottom of the balloon, and the balloon can then rise. The flight of hot air balloons is based on the principle of lift generated by hot air lighter than cold air and aerostatics. The gas temperature in the balloon is adjusted by ignition of the burner, the length of the time and frequency interval of the fire extinguishing, thereby controlling the rise and fall of the hot air balloon. The different wind directions of different height layers are used to control and adjust the direction of progress. The flight speed of the hot air balloon is roughly the same as the wind speed. The hot air balloon is heated by the balloon, hanging basket and heating.

　　The functions of hot air balloons are as follows:

　　1. The role in military aspects

　　Hot air balloons were initially used for communications and reconnaissance in the military. Due to the good performance of hydrogen balloons and long time of stagnation, they are widely used. However, hydrogen balloons have the disadvantages of being flammable and explosive, so more stable and safer helium balloons appeared in the 1920s. Hydrogen and helium balloons are mostly used in high-altitude scientific exploration.

　　2. Role in sports and tourism

　　Because the hot air balloon is simple to operate and has low requirements for takeoff and landing sites, it can be used for aviation sports and sightseeing, becoming a fashionable and healthy outdoor leisure sports. It allows tourists to see the panoramic view below from high altitude and photograph the beautiful scenery while also bringing a sense of comfort in drifting from high altitude.

　　The composition of hot air balloons

　　1. Hanging basket

　　The hanging basket is made of rattan and can relieve the impact when landing. Four special liquefied gas cylinders for hot air balloons are placed at the four corners of the hanging basket, and the meter is placed. The hanging basket is also equipped with a temperature gauge, altimeter, lifting gauge and other flight instruments.

　　2. Instruments

　　Altimeter: Altitude indicator; Lifting speed gauge: Shows the rising and falling speed; Thermometer: Indicates the air temperature in the balloon.　

　　3. Burner

　　The burner is the heart of the hot air balloon, and it burns compressed gas with energy 150 times larger than that of a general household gas furnace. The ignition burner is the fire of the main burner, which causes the internal air to heat up quickly to generate lift. In addition, there are two combustion systems on the hot air balloon to prevent failures in the air.

　　4. Ball

　　The balloon is a balloon's fabric part that carries hot air and is resistant to high temperatures. It is usually made of colorful nylon fabric. It is standard in the shape of water droplets. It can also be made into various special-shaped balls. The air contraction port is located on the top of the fabric, and the balloon can control the release of hot air.

　　It covers the air-contraction panels, sometimes called top hats, are the top of the umbrella, or spring top. The hot air balloon after opening is like a parachute, and the partially open parachute valve is a conventional method used to cool the air inside the balloon.