Chapter 14, Problem 14STP

To determine

The reason why a hot −air balloon descends when the burner is turned off while the balloon is in the air.

Explanation of Solution

Introduction:

The density of a substance is defined as the ratio of mass to volume of the substance.

  $\text{Density}=\frac{\text{Mass}}{\text{Volume}}$

The things that float on air are less dense than air. Due to low density of gas in balloon, it floats in the air.

When the burner is turned off then the temperature of balloon will go decreases and the air inside the balloon becomes cold heavy.As a result, the density of air inside the balloon becomes heavy as compare to air, which will help to descend the balloon.

Conclusion:

Thus, due to increase in density of air inside the balloon the balloon descends when burner turned off while the balloon is in air.