Chapter 15, Problem 91A

Interpretation Introduction

Interpretation: To explain the reason behind when pond water begins to mix when the ice melts.

Concept Introduction: On cooling a liquid, the density of the liquid increases gradually due to the movement of liquid molecules as they come to each other. If the process of cooling continues, the liquid solidifies into a solid, thereby having a greater density than the density of a liquid.

Due to this reason, the solid sinks into its own liquid as the density of the solid is greater than that of the liquid.

Answer to Problem 91A

In spring, when the ice melts and the temperature of the surface water increase to $\text{4°C}$ , it becomes heavier than the water below it and sinks.

Explanation of Solution

In spring, when the ice melts and the temperature of the surface water increase to $\text{4°C}$ , it becomes heavier than the water below it and sinks.

The surface water’s downward movement forces water inside the deeper parts of the lake.

Conclusion

In spring, when the ice melts and the temperature of the surface water increase to $\text{4°C}$ , it becomes heavier than the water below it and sinks.