How and why do hot air balloons float?
The balloons are filled with hot air. Hot air ls less dense than cool air. As you heat air, you are adding energy. The energy causes the molecules to move faster and bump into each other more frequently and with more force. This causes the air to spread out or expand. There is the same amount of air (mass) but it occupies more space (volume). This is what makes hot air less dense than cool air. Therefor, the hot air in the balloon will cause the balloon to rise and float. If you have ever noticed a hot air balloon in flight, you may have seen someone in the basket firing a burner system. This is because the air in the balloon will lose its heat to the surrounding cooler air and the balloon will begin to sink. To keep the balloon aloft, hot air must be replenished.
