How do balloons float?

Описание: Balloons float because they are filled with a gas that is *lighter than the surrounding air**, creating **buoyancy**. Earth’s air is mainly nitrogen and oxygen, which have weight. When a balloon is filled with a lighter gas such as **helium* or *hydrogen**, or when a **hot air balloon* heats the air inside it, the balloon becomes less dense than the air outside. According to **Archimedes’ principle**, any object in a fluid (and air behaves like a fluid) experiences an upward force equal to the weight of the air it displaces. If the balloon is lighter than the air it displaces, it rises.

With helium balloons, the helium molecules are lighter than air molecules. This makes the balloon weigh less than the air around it, so the buoyant force pushes it upward. Eventually, helium balloons fall when helium slowly leaks through the balloon material or when the gas cools and becomes denser.

Hot air balloons work differently. A burner heats the air inside the balloon, making it expand and become less dense. Warm air rises, so the balloon lifts off the ground. When the air cools or heat is reduced, the balloon becomes heavier, and it slowly sinks.

In short, balloons float because **lighter, less-dense gas rises above heavier surrounding air**.