Chapter 13, Problem 69A

Interpretation Introduction

Interpretation: Changes happening when a solid is heated to its melting point is to be explained.

Concept introduction:

The process of evaporation happens on the surface of a liquid since it transitions into the gas phase. Energy must be used to overcome the interactions between the particles in a liquid to allow them to be pulled apart and transformed into liquid.

Answer to Problem 69A

Because perspiration removes excess heat from the body.

Explanation of Solution

On a hot day, perspiration or sweating keeps our bodies cool because evaporation generates cooling. Therefore, when someone perspires or sweats, the sweat also evaporates by absorbing heat from the body's heat, keeping the skin's surface cold.

After perspiring, you start to cool down as your extra body heat is utilized to turn the sweat's beads into vapor.