Chapter U3.7, Problem 1E

Interpretation Introduction

Interpretation: The reason due to which hot air rises needs to be explained.

Concept Introduction:

The density of air is related to its mass and volume as follows:

  $d=\frac{m}{V}$

Here, m is mass and V is volume.

Answer to Problem 1E

The hot air rises because it becomes less dense.

Explanation of Solution

If temperature of the air increases, the kinetic energy of the molecules in air also increases. Due to increase in kinetic energy, the gases tend to expand and volume of air increases.

The density of the air is inversely proportional to volume, as mass of the air remains the same thus, density decreases due to increase in volume.

The less dense air tends to float over more dense or cold air therefore, the hot air rises.

Conclusion

Thus, the hot air rises because it becomes less dense.