Sorting becomes easier when materials are grouped by common properties such as use, state, whether they spoil quickly, and storage needs.
A useful sorting method is to group edibles by use and properties: cereals and pulses together, spices together, oils together, fresh fruits and vegetables separately, and perishable items in the refrigerator. Dry items should be kept in labelled, airtight containers. Items used often can be kept in front, while rarely used items can be kept behind.
Matter is anything that has mass and occupies space. A soluble material mixes completely in water. Transparent materials allow clear vision through them. Lustre means shine.
(i) T R E M A T - MATTER - (b) Occupies space and has mass; (ii) U L S B E L O - SOLUBLE - (d) Mixes completely in water; (iii) T N E R P A S N A R T - TRANSPARENT - (a) Objects can be seen clearly through it; (iv) E R U S T L - LUSTRE - (c) Shiny surface.
Since objects can be seen clearly through transparent materials, they are useful for storage containers.
Transparent containers allow us to see what is stored inside without opening them. They also help us check the quantity, colour, condition and cleanliness of the material quickly.
Wood blocks light, while glass generally allows clear vision. Aluminium foil is shiny, but an eraser is not. Sugar is soluble in water, while sawdust is insoluble. Matter occupies space and has mass.
(i) False. Wood is opaque while glass is transparent. (ii) True. (iii) True. (iv) False. An apple is matter because it occupies space and has mass.
The choice depends on material properties. Hard materials keep shape under load, lightweight materials are easy to move, poor heat-conducting materials feel less cold, and smooth/non-absorbent materials are easier to clean.
(i) Hardness: iron, wood, cement and stone. (ii) Lightweight: plastic and bamboo. (iii) Does not feel very cold during winters: wood, plastic and bamboo. (iv) Can be cleaned regularly and made to look new even after long use: plastic and iron.
The important properties are strength, hardness, whether the material leaks water, ease of cleaning, durability, weight and safety for the type of waste collected.
For food waste, a plastic or metal container with a lid is suitable because it should be washable, non-leaking and not easily affected by wet waste. For broken glass, a strong metal or thick plastic container is suitable because it should resist cuts and not break easily. For wastepaper, a cardboard, plastic or metal container can be used because the waste is dry and light.
- i. transparent, opaque
- ii. translucent, transparent
- iii. opaque, translucent
- iv. transparent, translucent
Air allows us to see clearly through it, so it is transparent. A wooden door does not allow us to see through it, so it is opaque.
(i) transparent, opaque
Hard materials do not easily change shape on pressing, while soft materials do. Soluble materials mix completely in water, while insoluble materials do not.
Material X can be sugar or salt crystals, and material Y can be cotton, sponge or rubber. Material X is hard because it is rigid and does not change shape easily when pressed. It is also soluble in water because it dissolves completely. Material Y is soft because it changes shape easily when pressed, and it is insoluble in water because it remains unchanged.
The clues point to material properties: lustre, compressibility, hardness, solubility, translucency and matter that may be invisible.
(i) (a) A metal such as aluminium or iron. (b) Sponge or foam. (c) Sugar or salt. (d) A translucent material such as butter paper. (e) Air. (ii) Example: I am transparent, hard and used in windows. Who am I? Glass.
Glucose dissolves in water and vinegar mixes with water. Mustard oil does not dissolve in water, and wheat flour does not dissolve completely in water.
Soluble pairs: glucose in water; vinegar in water. Insoluble pairs: mustard oil in water; wheat flour in water.