Unit 8: Fluids

Introduction

Fluids are substances that flow and conform to the shape of their container. This unit explores the internal structure and density of fluids, which are fundamental to understanding pressure, buoyancy, and fluid dynamics.

Key Concepts

• Fluids: Substances that flow (liquids and gases) and lack a fixed shape.
• Density (ρ): A measure of mass per unit volume: \[ \rho = \frac{m}{V} \] where ρ is density (kg/m³), m is mass (kg), and V is volume (m³).
• Comparing Densities:
  • Water: 1000 kg/m³ (standard reference)
  • Air: 1.2 kg/m³
  • Metals: Densities vary (e.g., iron 7874 kg/m³).
• Specific Gravity: The ratio of a substance’s density to the density of water: \[ SG = \frac{\rho_{\text{substance}}}{\rho_{\text{water}}} \]
• States of Matter in Fluids:
  • Liquids: Definite volume but take the shape of their container.
  • Gases: Expand to fill their container and are compressible.

Mathematical Routines

• Use ρ = m/V to calculate density.
• Compare densities using specific gravity.
• For floating objects, apply Archimedes' principle (covered in later sections).

Creating Representations

• Diagrams: Draw density comparisons for different materials.
• Graphs: Plot mass vs. volume to determine density (slope = ρ).

Scientific Questioning & Argumentation

• Why do objects with higher density than water sink?
• How does specific gravity help identify unknown substances?

Use density equations and experimental data to support your answers.

Practice Activities

Summary & Exam Preparation Tips

• Fluids include liquids and gases, which flow and take the shape of their container.
• Density is given by ρ = m/V and is crucial in determining sinking or floating.
• Specific gravity compares a substance’s density to water’s density.
• Knowing water’s density (1000 kg/m³) simplifies many fluid problems.