What is the central idea of the passage?

A porous clay jar cools its contents through evaporation, but its performance depends on the wall and surrounding air. (The passage explains the seepage-and-evaporation mechanism, then examines how humidity, airflow, glaze, and wall structure limit it.)

Why would the jar usually cool better in dry, moving air than in still, humid air?

Dry, moving air can accept and carry away more vapor, allowing evaporation to continue. (The text says humidity slows evaporation and airflow carries vapor away, so dry movement preserves the conditions for energy-removing evaporation.)

In this passage, what does “porosity” refer to?

The degree to which a material contains tiny connected openings (The porous wall contains connected spaces that let water seep outward, so porosity describes the presence and openness of those passages.)

According to the passage, what does glaze do to the cooling process?

It blocks the pores needed for water to seep outward. (The third paragraph explicitly states that glaze blocks the pores that make seepage, and therefore evaporation, possible.)

Why a Clay Jar Cools Water: Level 5 Reading Comprehension Questions

An unglazed clay jar can cool the water inside it without a motor or a block of ice. The explanation begins in the jar's porous wall. Tiny connected spaces let a small amount of water seep toward the outer surface. When water seeps through the clay, it spreads into a thin film exposed to the surrounding air.

Some molecules in that film move fast enough to escape as vapor. To escape, they take energy with them, leaving the remaining water and the jar slightly cooler. This transfer of energy is evaporative cooling, the same general process that makes damp skin feel cool in a breeze. Air movement helps by carrying away vapor near the surface, allowing more liquid water to evaporate.

The effect has limits. If the surrounding humidity is high, the air already contains abundant water vapor, so evaporation slows. Glaze also blocks the pores that make seepage possible. A very thick jar may move water too slowly, while a crack may release it too quickly. For that reason, potters must balance strength with porosity rather than simply making the wall as open as possible.

The jar does not manufacture cold; it exchanges a small amount of water for a loss of thermal energy. That distinction explains both its usefulness and its dependence on dry, moving air. A community workshop demonstrating the jar is therefore teaching material science, weather, and careful design through one quiet vessel.

Comprehension questions