Materials Around Us: questions with answers

Objects may be made up of one material or a combination of different materials. To compare the two objects, count the different material names in each description. Repeating the same material does not add another different material.

All things are made up of materials like paper, wood, cloth, glass, metal, plastic, and clay. A word in this group is a material example. A word such as pot, dish, bowl, or storage jar names an object, not the material itself.

The comparison is about the purpose of each balls and the properties needed for that purpose. Materials are chosen depending on their properties and the purpose for which the object is to be used.

A material should be chosen according to its properties and the purpose for which the object is to be used. For a chair, the useful property here is that the material should be easy to lift or take from one place to another. So plastic is the best fit among these choices.

Different materials may be considered for the same object, but the choice should depend on the purpose. Here the important property is that the material should be lightweight. So plastic is better than stone for a chair that is easy to lift.

Materials that are difficult to compress or scratch are hard. Material Y is difficult to compress and difficult to scratch, so it is hard. Pressing and scratching are both useful tests of hardness, so neither test can be called useless.

Soft materials can be compressed or scratched easily. Hard materials are difficult to compress or scratch. Use both observations before choosing the name. Here the material is hard because it is difficult to compress and difficult to scratch.

Air allows clear viewing. Frosted glass and butter paper are translucent; wood is opaque.

Air is transparent because objects can be seen clearly through it. The wooden door is opaque because objects cannot be seen through it.

The observation gives the rule to use. A material that completely disappears in water is soluble. A material that does not disappear even after being stirred for a long time is insoluble.

Liquid P settled as a separate layer when the beaker was left undisturbed. Some liquids do not mix with water and stay as a separate layer, however long they are stirred. Liquids can be checked for mixing with water just as solids can. So the correct label is: does not mix with water and forms a separate layer.

A soluble material dissolves in water and completely disappears. An insoluble material does not mix with water and does not disappear even after being stirred for a long time. The observation the material completely disappears in water shows that the material is soluble in water.

The pan that goes down holds the heavier object, and the heavier object has more mass. No numbers are needed to compare.

Both tumblers are identical, so the water level is the useful cue. The higher water level shows a greater amount of water. The space occupied by water is its volume.

The units to measure volume are litre (L) and millilitre (mL). A bottle label shows how much liquid the bottle holds, so it uses one of these units. A label reading 5 is written as litre (L). Gram (g) and kilogram (kg) are not volume units, and 'bottle' is the container, not a unit.