Why do hot air balloons float in the air?

• A. The balloon material repels gravity, allowing it to float.
• B. The heated air inside the balloon is less dense than the cooler air outside, causing the balloon to rise.
• C. The hot air inside the balloon creates a vacuum that lifts the balloon.
• D. The balloon is filled with helium, which is lighter than air.

Answer: (B)

Verified step by step guidance

1. Understand the principle of buoyancy, which states that an object will float if it is less dense than the fluid (in this case, air) surrounding it.
2. Recognize that heating the air inside the balloon causes the air molecules to move faster and spread apart, decreasing the density of the air inside the balloon compared to the cooler air outside.
3. Apply the concept that the less dense hot air inside the balloon creates an upward buoyant force because the cooler, denser air outside pushes the balloon upward.
4. Note that the balloon material itself does not repel gravity; rather, the difference in air density is what causes the balloon to rise.
5. Conclude that the balloon floats because the heated air inside is less dense than the surrounding cooler air, not because of a vacuum or helium gas.