Class 6 Science Chapter 2 Important Questions

It helps to collecting information and gaining systematic knowledge of things as possible. It helps in dividing materials in groups makes it convenient to study their properties. It is convenient to work with all materials or members of a group after knowing their properties.

We see around us, chair, bullock cart, cycle, cooking utensils, books, clothes, toys, water, stones and many other objects.

Objects that are made of plastics such as buckets, lunch boxes, toys, water containers, pipes and many objects. Objects that are made of wood such as chair, table, plough, bullock cart and its wheels, matchbox, and many objects.

All objects around us are made of one or more materials. These materials may be chair, table, plough, bullock cart and its wheels. All objects are made up of wood. And books, notebooks, newspaper, toys, calendars are made up of paper.

First, we grouped objects in many different ways. We then found that objects around us are made of different materials. At times, an object is made of a single material. An object could also be made of many materials. And then again, one material could be used for making many different objects.

We should keep in mind that we generally use a tumbler to keep a liquid. Therefore, it would be silly, if we were to make a tumbler out of cloth. We need for a tumbler is glass, plastics, metal or other such material that will hold water.

Collect small pieces of different materials – paper, cardboard, wood, copper wire, aluminium sheet, chalk. Separate the shiny materials into a group. Now, cuts each material into two pieces and look at the freshly cut surface. Some of these materials are appear shiny. Include these objects also in the group of shiny materials. Instead of cutting, you can rub the surface of material with sand paper to see if it has lustre. Materials that have such lustre are usually metals. Iron, copper, aluminium and gold are examples of metals. Therefore, we can differentiate the materials, according to the lustre.

When you press different materials with your hands, some of them may be hard to compress while others can be easily compressed. Take a metal key and try to scratch with it, the surface of a piece of wood, aluminium, a piece of stone, a nail, candle, chalk, any other material or object. You can easily scratch some materials, while some cannot be scratched so easily. Materials which can be compressed or scratched easily are called “soft” while some other materials which are difficult to compress are called “hard”. For example, cotton or sponge is soft while iron is hard.

Water which is known as “universal solvent” as it can dissolve maximum materials.

The name of the gas is oxygen which dissolved in water and very important for the survival of animals and plants that live in water.

Objects that float in water: plastic, wood, oil, sponge, petrol, kerosene, wax, ships etc.
Objects that sink in water: rock, marble, steel, iron, copper, nickel, sand, mercury etc.

Transparent: Those substances or materials, through which things can be seen, are called transparent. Glass, water, air and some plastics are examples of transparent materials.
Shopkeepers usually prefer to keep biscuits, sweets and other eatables in transparent containers of glass or plastic, so that buyers can easily see these items.

Take a sheet of paper and look through it towards a lighted bulb. Now, put 2-3 drops of some oil and spread it on the sheet of paper. Look again towards the lighted bulb through that portion of the paper on which the oil has been spread. You will be find that the bulb is more clearly visible than before. But, not clearly through the oiled paper.
Generally, the materials through which objects can be seen, but not clearly, are known as translucent material.

Opaque: Card-board, Bricks, Plywood, Mirror, Stone.

Transparent: Air, Water, Glass

Translucent: Oily paper, Polyethene, Frosted glass.

As we know that in everyday life, we often group materials for our convenience. At home, we usually store things in such a manner that similar objects are placed together. Such an arrangement helps us to locate them easily.
Similarly, a grocer usually keeps all type of biscuits at one corner of his shop, all soaps at another while grains and pulses are stored at some other place. Materials differ in their appearance and the way they mix in water or other liquids. They may float or sink in water or may be transparent, opaque or translucent. Materials can be grouped on the basis of similarities or differences in their properties.
There is another reason why we find such grouping useful as dividing materials in groups makes it convenient to study their properties and also observe any patterns in these properties.

Some metals often lose their shine and appear dull, because of the action of air and moisture on them.
Some metals as a result of oxidation with the atmospheric oxygen form oxides and by which their appearance becomes dull.

(a)
Round shape: basketball, orange, globe, apple, earthen pitcher
Other shape: Water, sugar
(b)
Eatable: Water, orange, sugar, apple
Non-eatable: Basket-ball, globe and earthen pitcher

Oxygen gas dissolves in water i.e. oxygen gas is soluble in water. The plants and animals which live in water use the oxygen dissolved in water for respiration. Thus, oxygen gas dissolved in water is very important for the survival of animals and plants that live in water.

Cotton ball initially floats on water but after few minutes (i.e. 10 min. to 15 min.), its sinks because it absorbs water.

Generally, when we are playing hide and seek, we choose an opaque place to hide because an opaque material does not allow light to pass through them due to which the object or person behind them cannot be seen.
If we choose transparent materials to hide, person can be seen easily because transparent materials, allow almost all the light to pass through them. Therefore, in the hide and seek game we would always prefer to choose an opaque place to hide.