Classifying Objects by Properties

Scientists sort objects into groups all the time. This is called classifying. When we classify, we choose one property — like color, size, shape, or texture — and use it to sort everything into groups.

What is classifying?

• Classifying means putting objects into groups based on a shared property.
• The same set of objects can be classified in many ways — by color, by size, by shape, or by texture.
• Example: A library classifies books by subject. A grocery store classifies food by type. Scientists classify materials by properties.

The property: Hard vs Soft

• A hard material resists being scratched or squeezed — it keeps its shape when you press it. Examples: rock, metal, glass, brick, wood.
• A soft material changes shape easily when pressed or squeezed — it compresses. Examples: cotton, foam, sponge, feather, clay, fabric.
• Test: press your finger against the object. Does it dent? → soft. Does it stay rigid? → hard.

Why does classification matter?

• Classifying helps scientists find patterns — all hard materials tend to be good for building; soft materials tend to be good for cushioning.
• Engineers choose materials by their classification: a bridge needs hard materials; a pillow needs soft ones.

Tricky cases

• Wood — can feel smooth and semi-soft on the surface, but a wooden plank is classified as hard because it does not compress.
• Rubber — flexible but also quite resistant; some rubbers are classified as hard, others as soft depending on the type.