The Amazing World of Solutes, Solvents, and Solutions | Class 8 Science Notes

9.5.3 Effect of pressure on density

This section describes how pressure influences density differently depending on the state of matter. For gases, increasing pressure compresses the particles closer together, reducing volume and increasing density significantly. Liquids are nearly incompressible, so pressure has a minimal effect on their density. Solids are even less affected by pressure due to their tightly packed particles, and changes in their density are usually negligible. The section also explains the special case of water and ice: ice floats on water because it is less dense. Water has its highest density at 4 °C; as it freezes at 0 °C, it expands due to a change in molecular structure, decreasing density. This property is crucial for aquatic life, as floating ice insulates water below, allowing fish and other organisms to survive in cold climates. The section encourages students to think about density by experimenting with sinking and floating eggs in water.

📊 Diagram: Fig. 9.23: Ice floats on water; Fig. 9.24: Raw whole egg sinks in water

🧪 Activity: Think like a scientist: Observing sinking and floating of eggs in water and saltwater.

🔗 Connection: Summarizes key concepts and introduces review questions in the summary section.