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Science: Class 6 — Chapter 6: Materials Around Us

6.1 Observing Objects Around Us
  • Material: Any substance used to create an object is referred to as a material (e.g., paper, wood, cloth, glass, metal, plastic, clay).
  • Objects around us are made of different materials, and a single material can be used to make many different objects.
6.2 How to Group Materials?
  • Classification: The method of arranging objects into groups based on common properties (such as shape, colour, hardness, or material type).
  • Classification helps in systematically studying and observing patterns in the properties of things.
6.3 Properties of Materials

6.3.1 Appearance (Lustre)

  • Lustrous: Materials that have a shiny appearance, typically metals (e.g., iron, copper, aluminium, gold). Some metals may lose lustre due to exposure to air and moisture.
  • Non-lustrous: Materials that do not have a shiny surface (e.g., paper, wood, rubber, jute).

6.3.2 Hardness

  • Soft: Materials that can be easily compressed or scratched (e.g., eraser, sponge, candle, chalk).
  • Hard: Materials that are difficult to compress or scratch (e.g., stone, iron, wood). Hardness is a relative property.

6.3.3 Transparency

  • Transparent: Materials through which things can be seen clearly (e.g., glass, water, air, cellophane paper).
  • Opaque: Materials through which you cannot see at all (e.g., wood, cardboard, metals).
  • Translucent: Materials through which objects can be seen, but not clearly (e.g., butter paper, frosted glass).

6.3.4 Solubility in Water

  • Soluble: Materials that completely dissolve and disappear when mixed in water (e.g., sugar, salt, glucose).
  • Insoluble: Materials that do not mix or disappear even after stirring for a long time (e.g., chalk powder, sand, sawdust).
  • Some liquids (like vinegar) and gases (like oxygen) dissolve in water, which is crucial for aquatic life.
  • ORS (Oral Rehydration Solution): Prepared by mixing six teaspoons of sugar and half a teaspoon of salt in one litre of boiled and cooled water.

6.3.5 Mass and Volume

  • Mass: A property that quantifies the amount of matter present in an object, determining how heavy or light it is. Measured in grams (g) and kilograms (kg).
  • Volume: The space occupied by matter. Measured in litres (L), millilitres (mL), or cubic metres (m³).
6.4 What is Matter?
  • Matter: Anything that occupies space and has mass is called matter. All materials are types of matter.
  • SI Units: The standard unit of mass is the kilogram (kg). The SI unit for volume is the cubic metre (m³), where 1 m³ = 1000 L.
Historical & Traditional Insights
  • Ancient Pottery: Dates back 7,000 to 8,000 years in the Ganga plains (Lahuradewa) and Baluchistan (Mehrgarh). Developed advanced techniques during the Harappan Civilisation using baked clay (terracotta).
  • Ayurvedic Classification: Ayurveda describes physical matter using 20 properties (guṇa), arranged in 10 pairs of opposites (e.g., heavy/light, cold/hot, solid/liquid, soft/hard).