Materials Around Us - Observing Objects Around Us

Objects are the things we see around us (e.g., chairs, books, toys). These objects are made of one or more substances called Materials (e.g., wood, plastic, metal).

Classification is the systematic grouping of objects based on similarities and differences in their properties. This helps in identifying and studying objects easily.

Appearance (Lustre): Some materials shine and are called lustrous. Metals like $\text{Gold (Au)}$, $\text{Silver (Ag)}$, and $\text{Iron (Fe)}$ exhibit lustre. Materials that do not shine are called non-lustrous.

Hardness: Materials that can be easily compressed or scratched are called Soft (e.g., Cotton). Materials that are difficult to compress are called Hard (e.g., Iron, Diamond).

Solubility: Substances that dissolve completely in water ($H_2O$) are called Soluble (e.g., Sugar, Salt/$\text{NaCl}$). Substances that do not dissolve are called Insoluble (e.g., Sand, Chalk powder).

Buoyancy (Float or Sink): Objects with a density $\rho$ less than the density of water will float, while those with a higher density will sink.

Transparency: Materials like glass that allow light to pass through completely are Transparent. Materials that do not allow any light to pass are Opaque (e.g., Wood, Metal). Materials that allow light to pass partially are Translucent (e.g., Oiled paper).