Ch 4 teaches students to classify materials based on their properties like appearance, hardness, solubility in water, transparency, and whether they float or sink.
Materials can be grouped by: lustre (shiny vs dull), hardness (hard like iron vs soft like sponge), solubility (sugar dissolves in water, sand does not), transparency (transparent, translucent, or opaque), and ability to float or sink.
Transparent materials let light pass through completely (glass, water). Translucent materials let some light through (frosted glass, oiled paper). Opaque materials block light completely (wood, metal).
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Transparent materials let all light pass through — you can clearly see objects on the other side (e.g., glass). Translucent materials let some light through but scatter it — objects appear blurry (e.g., frosted glass, oiled paper).
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