The heat source for filling the envelope with hot air.

The heat source for filling the envelope with hot air.

• A. Burner
• B. Altimeter
• C. Balloon
• D. Wave

Answer: (A)

To lift a hot-air balloon, you heat the air inside the envelope. The heat source is the burner, which produces a flame to warm the air inside the envelope. As the air gets hotter, it becomes less dense than the surrounding cooler air, creating buoyant lift that fills and inflates the envelope. The altimeter is just a tool to measure altitude, not to heat. The balloon refers to the fabric envelope that contains the hot air, not the heat source. A wave has no role in filling the envelope with hot air.

To lift a hot-air balloon, you heat the air inside the envelope. The heat source is the burner, which produces a flame to warm the air inside the envelope. As the air gets hotter, it becomes less dense than the surrounding cooler air, creating buoyant lift that fills and inflates the envelope. The altimeter is just a tool to measure altitude, not to heat. The balloon refers to the fabric envelope that contains the hot air, not the heat source. A wave has no role in filling the envelope with hot air.