How does a hot air balloon work?

Why does a balloon fly? A balloon works according to a basic law of physics — warm air is lighter than cold air. This means that any “bubble” of warm air in the atmosphere will always rise. By adjusting the amount of warm air and the temperature difference between the air inside the balloon and the air outside, the pilot can easily control the altitude. Thanks to modern technology and perfectly refined burner and fuel systems, temperature control — even in very large balloons — can be achieved with an accuracy of up to 0.5 degrees. This allows for precise control of the flight altitude.
However, direction and speed are a different story. Here, we still rely on the forces of nature — our knowledge of meteorology helps us predict wind directions and speeds at different altitudes.