When you heat the air inside the balloon, the molecules move faster and spread farther apart which means that there are fewer molecules inside the balloon than outside making it lighter. To keep the molecules far apart, propane burners keep the air hot as the balloon rises. The only way to steer the balloon is to use the wind. The wind’s directions change between altitudes so you move upwards and downwards to move left and right. To move up, you provide more heat, when you want to move down, you open a hatch on the side of the balloon to let hot air out.

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