Positive buoyancy of an airborne COTA exists when the ambient air density is ____ the density of the airborne COTA.

Positive buoyancy of an airborne COTA exists when the ambient air density is ____ the density of the airborne COTA.

• A. greater than
• B. less than
• C. equal to
• D. unrelated to

Answer: (A)

Positive buoyancy occurs when the object or plume is less dense than the surrounding air, so the buoyant force from displaced air exceeds its weight and it rises. If the ambient air density is greater than the density of the airborne COTA, the COTA is lighter than the surrounding air and will ascend due to this buoyant force. If the ambient density were lighter than the COTA, the plume would have negative buoyancy and tend to sink; if densities were equal, it would be neutrally buoyant and neither rise nor sink.

Positive buoyancy occurs when the object or plume is less dense than the surrounding air, so the buoyant force from displaced air exceeds its weight and it rises. If the ambient air density is greater than the density of the airborne COTA, the COTA is lighter than the surrounding air and will ascend due to this buoyant force. If the ambient density were lighter than the COTA, the plume would have negative buoyancy and tend to sink; if densities were equal, it would be neutrally buoyant and neither rise nor sink.