A sealed hot air balloon is capable of rising to high altitudes when it is initially released. As the air in the balloon cools, however, it eventually comes back down to the ground because
A) what goes up must come down.
B) objects heavier than air can only fly through the air with the help of a motor.
C) the object comes down when the air in it eventually leaks out.
D) objects can only float in a fluid if their density is less than that of the fluid.
Fill in the Blank Questions

Question

Quizplus · Accepted Answer

The principle that allows hot air balloons to rise is that warm air is less dense than cooler air. As the air inside the balloon cools, its density increases. When the density of the air inside the balloon becomes greater than the density of the surrounding air, the balloon loses its buoyancy and begins to descend. This is because objects (or substances) can only float in a fluid (gas or liquid) if their density is less than that of the fluid.

A Sealed Hot Air Balloon Is Capable of Rising to High