Hot-air balloons are used as entertainment in tourist spots in Egypt, Turkey and many other countries. For the balloon to rise in the air, the balloons are filled with hot air at 90o C. Since the hot air’s density is less than the cold air’s density in the surrounding area, the balloons rise and float into the air. If they have to be kept at a particular height, the burner below the mouth of the balloon is put off. If it has to be elevated to greater height, it is started again. The balloon must have a minimum size so that it can overcome the force of pull of gravity of the Earth.
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