Balloon

A balloon is a flexible bag or cloth filled with air, gas, or breath that then takes on a rounded shape. Common balloons are small, made from latex rubber, and used at celebrations, festivals, and children's games. There are also large balloons that can carry people or equipment, known as hot-air balloons.

A balloon works on the principle of density difference between the gas inside and the weight of that gas compared to the outside air. If the gas inside is lighter than the air—such as helium or heated air—the balloon rises. If filled with ordinary air, the balloon does not rise but simply takes on a rounded form.

Types

Balloons sold on the market are usually made from latex, a rubber derived from the rubber tree. There are also balloons made from thin film (foil or Mylar) that resists gas escape, allowing them to remain inflated for longer periods. Large weather balloons used in atmospheric research are constructed from lightweight material that contains the gas.

Hot-air balloon

A hot-air balloon has a large bag (envelope) and a burner that heats the air inside. Hot air is lighter than the cold air outside, which provides the lift. The pilot changes altitude by increasing the flame or opening a vent at the top to let hot air escape. Wind direction determines the horizontal course at different atmospheric levels.

Scientific use

Weather balloons carry small instruments (radiosondes) that measure temperature, humidity, and air pressure as they rise. This data is transmitted by radio to weather stations. Very large balloons that reach the upper atmosphere are also used in astronomical research and remote sensing.