(a) Same
Same materials can be used fpr made up more than one things.

(a) depending on its properties
We choose a material to make an object depending on its properties.

(a) iron
Books, notebooks, calendar and newspapers etc, are made by paper.

(a) shining
Iron, aluminium and gold have shining appearance.

(b) lustrous materials
Materials which have lustre are called lustrous materials.

(b) non-lustrous
Wood and stone is non-lustrous materials.

(a) surface
We see lustre on the freshly cut surface.

(d) sugar
Sugar is dissolve in water.

(a) due to oxygen gas dissolved in water
Aquatic animals survive in water due to oxygen gas dissolved in water.

(a) wood
A wood is an object that floats in water.

(b) crystals
Crystals sinks in water.

(a) vinegar
Vinegar mixes well in water.

(c) glycerin
Glycerin does not mix well in water.

(a) soluble
The substances dissolves in water are soluble substances.

(b) insoluble
The substances do not dissolves in water are insoluble substances.

(c) lustre
Some materials have special shine on them which is called lustre.

(a) hard
Materials which are difficult to press are called hard.

Important Questions

Objects around us

Question 1.
What do you mean by classification?
Answer:
Classification is the grouping or sorting together of things possessing similar or dissimilar characteristics or properties.

Question 2.
What is the need for classification?
Answer:
Classification is essential for:

• identification of objects.
• sorting of objects.
• locating things.
• understanding similarities and dissimilarities among objects.
• making the study of objects easy and more meaningful.

Question 3.
Why is mercury used in making thermometers?
Answer:

• Mercury is liquid at room temperature.
• It is a good conductor of heat.
• Mercury has lustre, so, it is easy to read the temperature shown by the level of mercury.

Question 4.
On what basis are the various objects grouped?
Answer:
The grouping of various objects can be done on the basis of following characters:

• size
• shape
• colour
• hardness
• solubility in water
• attraction towards magnet
• conduction of heat
• transparency, etc.

Question 5.
Why do we need the grouping of objects?
Answer:
Grouping the objects helps us to arrange them in a systematic manner. The objects when grouped are easy to handle. When grouped, it is easy to know the properties of an object clearly. Grouping also makes easy to compare two objects.

Question 6.
How does the grouping of objects help the shopkeeper?
Answer:
The grouping of objects in proper way makes it easier to work. When we go to purchase some things, the shopkeeper locates it easily, because there are separate shelves to put various items and similar things are kept at one place. If he randomly places all of these, he would never be able to find them so quickly and easily.

Question 7.
Name the various materials from which following things can be made:
Shoes, chair, coins, utensils, clothes.
Answer:

• Shoes: Leather, rubber, plastic, canvas
• Chair: Wood, metal, plastic, concrete
• Coins: Copper, silver, gold
• Utensils: Iron, copper, aluminium
• Clothes: Cotton, wool, silk, rayon, nylon.

Question 8.
Name any four materials that can be used to make school bags.
Answer:
Cloth (of cotton, jute, nylon, etc.), plastic, metal or alloy.

Question 9.
List any three solutions that are used in your home.
Answer:
Salt solution, sugar solution, cold drinks, lime juice, etc.

Question 10.
Why is water important for our body?
Answer:
Water can dissolve a large number of substances, so it is needed by the body. It is also major part of our body cells.

Activity 2
Table 4.2 lists some common materials. You can also add more materials in Column 1 that are known to you. Now, try and think of everyday objects you know, that are made mainly of these materials, and list them in Column 2.

Table 4.2: Different types of objects that are made from the same material

Properties of materials

Question 1.
List five each opaque and transparent materials.
Answer:
Opaque materials:

• Wood
• Iron
• Cardboard
• Brick
• Gold.

Transparent materials:

• Water
• Glass
• Air
• Cellophine plastic, and
• Fibre glass.

Question 2.
List five objects that are made from transparent materials.
Answer:

• Beaker,
• Test tube,
• Conical flask,
• Glass jug, and
• Glass doors.

Question 3.
List five liquids that are transparent.
Answer:

1. Water
2. Hydrochloric acid
3. Alcohol
4. Acetone, and
5. Petrol.

Question 4
List five objects that are made from an opaque material.
Answer:

1. Books
2. Blackboard
3. Cardboard
4. Wall, and
5. Wooden furniture.

Question 5.
Why is water called universal solvent?
Answer:
The property of water to dissolve large number of materials makes it a universal solvent.

Question 6.
List three liquids which are miscible in water.
Answer:

1. Milk
2. glycerine, and
3. soft drinks.

Question 7.
List three liquids which are immiscible in water.
Answer:

1. Edible oil
2. kerosene oil, and
3. petrol.

Question 8.
State conditions when pure water can lose transparency.
Answer:
Water on cooling, freezes to form ice which is not transparent.

Question 9.
List the following substances as soluble and insoluble in water.
Sand, salt, sugar, paint, chilli powder, desi ghee, blotting paper.
Answer:
Water soluble substances: Salt, sugar.
Water insoluble substances: Sand, paint, chilli powder, desi ghee, blotting paper.

Question 10.
Show that sugar, common salt and washing soda are soluble while chalk powder, iodine and sand are insoluble in water.
Answer:
Take six test tubes, fill each of them about half with water. Keep each of them in a test tube stand. Add a pinch of each of six substances in separate test tubes. Shake well and allow to stand for few minutes. Common salt, sugar and washing soda dissolve while iodine, chalk powder and sand do not dissolve.

Question 11.
Describe a method to prove that water is a transparent material.
Answer:
Take a white sheet of paper, one sketch pen, one clean beaker and a small quantity of clean water. Now on white sheet mark a symbol (say “X’). Now put the empty beaker over the marked symbol. We can see it properly. Now put water in the beaker. Observe the same mark. The mark is again visible. This observation proves that water is transparent.

Question 12.
Why is a tumbler not made with a piece of cloth?
Answer:
This is because we generally use a tumbler to keep a liquid. A tumbler made of a piece of cloth cannot be used to keep water. So, a tumbler is made with a material which has a property to hold the liquid.

Question 13.
Explain with example rough and smooth surfaces.
Answer:
Rough surface: Materials which have uneven surface or ridges can be termed as a rough surface, e.g., coal.
Smooth surface: Materials which are plain and have an even surface are termed as a smooth surface, e.g., marble.

• Appearance
• Hardness
• Solubility or insolubility
• Float or buoyancy
• Transparency.

Question 14.
Name two gases each which are soluble and insoluble in water. «
Answer:
Gases soluble in water are oxygen and carbon dioxide. Gases insoluble in water are hydrogen and nitrogen.

Question 15.
Write any four properties of materials.
Answer:
Four properties of materials are:

1. Appearance
2. Hardness
3. Solubility or insolubility
4. Float or buoyancy
5. Transparency.

Question 16.
What are the similarities between iron, copper, aluminium?
Answer:

• They all have lustre.
• They all are metals.
• They are hard.

Activity 3.
Collect small pieces of different materials—paper, cardboard, wood, copper wire, aluminium sheet, chalk. Do any of these appear shiny?
Now, observe as the teacher cuts each material into two pieces and look at the freshly cut surface (NCERT Fig. 4.3). What do you notice? Does the freshly cut surface of some of these materials appear shiny?
Yes. Copper wire.

Activity 4.
Collect samples of some solid substances such as sugar, salt, chalk powder, sand and ; sawdust. Take five glasses or beakers. Fill each one of them about two-thirds with water. ) Add a small amount (spoonful) of sugar to the first glass, salt to the second and similarly, | add small amounts of the other susbtances into the other glasses. Stir the contents of each of them with a spoon. Wait for a few minutes. Observe what happens to the substances added to water (Fig.). Note your observations as shown in Table 4.3.

Activity 5.
Collect samples of vinegar, lemon juice, mustard oil or coconut oil, kerosene or any other liquid. Take a glass tumbler. Fill it up to half with water. Add a few spoonfuls of one liquid to this and stir it well. Let it stand for five minutes. Observe whether the liquid mixes with water (see figure). Repeat the same with other liquids, as many different liquids as are available to you. Write your observations in Table 4.4.

Table 4.4: Solubility of some common liquids in water