Recognizing Useful and Harmful Materials

Materials are considered useful when they serve a purpose. Materials may have durability, resistance to water, heat, or acid, flexibility,  elasticity, and hardness.

 Some useful materials may also bring hazards, For example, a broken glass jar can cause cuts or injury. Toxic substances may also be present in the things you commonly use such as paints, cleaners, fumes, gels, or powders.

 When a material already served its primary use and can be discarded, it is considered a waste. Waste can be classified as biodegradable and non-biodegradable. Generally, biodegradable materials can be decomposed by bacteria or other living things. Examples include fruit peelings, dried leaves, leftover food, paper, and the like. Non- biodegradable materials do not rot easily. Examples are plastic, styrofoam, cans, glasses, and the like.

 Waste materials are safely disposed of in a landfill. A landfill is a dumping site where waste materials are covered with layers of soil. This is done so as not to pollute the surrounding land.

Properties of Useful materials

Hardness - the ability of a material to resist pressure ( metals, wood & stones are hard)

Malleability - the ability of a material to be pounded into thin sheets

( gold, silver, and copper are materials that can be formed into different jewelry or ornaments. Iron can be hammered into thin sheets that can be used as roofs, gates, and body parts of machines.

 Ductility - the ability of a material to be drawn into thin wires ( iron, brass, and tungsten are ductile materials. They are used in electrical wiring at home nad filament of bulbs. The wires in your headphones, cell phone chargers, and electric cords of appliances are products of ductile materials.

Porosity - the ability of a material to allow water and gases to pass through it

( clothes, sponges, mops, tissue paper) Plastic and glass are nonporous.

Flexibility - the ability of a material to bend or roll without breaking easily. ( wire, rubber, cloth, and some plastics are flexible materials that can be folded, pressed, or stored in any form without breaking. Materials used in making bags, belts, clotheslines. and tents are flexible materials.

Elasticity - is the ability of a material to return to its size and shape without breaking after it is stretched, pressed, or twisted. ( rubber is an elastic material that is used for making rubber bands, and rubber belts used in some machines. rubber shoes, and stretchable bags.

Thermal conductivity - the ability of a material to transfer heat from one area to another