When the air under the envelope is heated, the balloon lifts, Which of the following statements is true?
A. Hot air balloons use radiation to rise
B. Hot air balloons use conduction to rise
C. Hot air balloons use convection to rise**
D. Hot air balloons use air resistance to rise
Right!
c.Hot air balloons use convection to rise**
To determine which statement is true, we need to understand the process of how a hot air balloon rises. The correct answer is C. Hot air balloons use convection to rise.
Explanation:
Hot air balloons work on the principle of convection. Convection is the transfer of heat through the movement of a fluid (in this case, air) caused by differences in temperature. Here's how it works:
1. Heating the air: The burner at the bottom of the balloon generates a flame, which heats the air inside the envelope (the fabric part of the balloon).
2. Expansion of air: As the air inside the envelope is heated, it expands and becomes less dense. This decrease in density makes the heated air lighter than the surrounding cooler air.
3. Buoyancy: The lighter, heated air inside the envelope is now buoyant and starts to rise above denser, cooler air. This is because hot air is less dense and creates an upward force known as buoyancy.
4. Vertical motion: As the hot air rises, it displaces the cooler air above it, creating an upward airflow. This upward airflow is known as convection.
5. Sustained lift: The upward convection current continues to lift the balloon as long as the burner is providing heat, and the temperature difference between the inside of the envelope and the outside air is maintained.
Based on this explanation, we can conclude that hot air balloons use convection to rise.