This makes the air lighter, or less dense, so it rises. As air cools, it becomes heavier, or more dense, and sinks. As warm air rises, air from cooler areas flows in to take the place of the heated air. This process is called convection and causes air to move. The differential heating of the Earth's surface and the resulting convection is what causes wind on this planet.
Wind circles the Earth and plays an important role in determining weather conditions.
The hot air inside is lighter or less dense than the cooler air outside the balloon. As the hot air rises, it carries the balloon upward. When the gas flame is turned down, the air cools and the balloon sinks back to the ground. Coastal winds blow landward during the day and seaward at night. On a sunny day, the sand warms quickly.