Physical Properties of Materials

We generally use a tumbler to keep liquid. Therefore, would it not be silly, if we were to make a tumbler out of cloth. What we need for a tumbler is glass, plastics, metal or other such material that will hold water. Similarly, it would not be wise to use paper-like materials for cooking vessels.

Using a cloth as a tumbler 

We see then, that we choose a material to make an object depending on its properties, and the purpose for which the object is to be used. Different types of materials have different properties such as appearance, solubility, transparency, conductivity and behaviour towards magnet etc.

Lets study these properties one by one.

1.0Appearance

Materials usually look different from each other. Mud looks different from wood. Wood looks different from plastics. Plastics look different from copper. Copper looks different from iron or aluminium.

However, there might be some similarities between copper, iron and aluminium that are not in the plastics, wood or mud.  

Copper, aluminium and iron, the sand-papered surface is shining. The special kind of shine present on natural materials or shine appears when they are freshly cut or sand papered is called lustre.  The materials which have natural shine on their surface or the shine appears when they are freshly cut or sandpapered are called lustrous materials. Due to lustrous nature of metals of gold, silver, copper, and platinum are used in making jewellery.

(a) Among the solids, all metals have a lustre. Generally, this lustre is silvery white, except gold and copper which have a yellow and reddish lustre respectively. Graphite (a physical form of carbon) and iodine crystals have lustre. Similarly, gems and pearls are lustrous.

(b) Amongst the liquids, mercury (it is a liquid metal) is lustrous. 

(c)All gases are non-lustrous.

2.0Hardness

You must have experienced that if you press a piece of foam with your thumb it gets pressed, but a piece of stone or wood does not get pressed. You can say that a piece of wood or stone is harder than a piece of foam. However, how shall we find which amongst wood or stone is harder?

The best way of finding it out is to scratch the wood against the stone. If the wood gets scratched by stone, then the stone is harder than the wood. When the surfaces of two different materials are rubbed against 

each other, then the surface which scratches is said to be hard and the property is called hardness of the material.

Conversely, the surface which gets scratched is said to be soft as compared to the scratching surface.

For example,

(a) Diamond is the hardest naturally occurring substance. Among the different kinds of diamonds, black diamond is the hardest. 

(b) Glass is also a hard substance, still diamonds can be used to scratch glass and hence are used for cutting glass.

(c) Talc obtained from soapstone is the softest substance. Soapstone is a magnesium rich metamorphic rock from which talc is obtained.

3.0Soluble or Insoluble in Water

It is a common experience that when we put a spoonful of common salt or sugar into a tumbler filled with water and stir the contents, the sugar or the common salt completely disappears.

Soluble substances: The substances which completely dissolve in water are called soluble substances. They form a uniform mixture with water called homogeneous mixture.

For example, Sugar, Common salt, Washing soda etc.

Solubility: The property of substance due to which it dissolves in water is called solubility.

Insoluble substances: The substances which do not dissolve in water are called insoluble substances. They form a non-uniform mixture with water called heterogeneous mixture.

For example, sand, chalk, etc

Solubility of Liquid Substances in Water

Most of the liquids are insoluble in water. However, liquids such as alcohol, vinegar, lemon juice etc., dissolve in water.

The liquids which dissolve in water are called miscible liquids.

The liquids which do not dissolve in water are immiscible liquids. 

Liquids such as kerosene oil, coconut oil, petrol, ether, benzene, etc., are not miscible with water. However, they are easily miscible with one another. For example, coconut oil is easily miscible in kerosene oil, petrol, ether, and benzene.

Solubility of Gases in Water

Most of the gases are insoluble in water. For example, nitrogen, hydrogen, and carbon monoxide are insoluble in water. However, some gases are soluble in water.

Oxygen gas is slightly soluble in water. It is the oxygen dissolved in water which enables the fishes and other aquatic animals to breathe with the help of their gills.

Carbon dioxide gas is slightly soluble in water. It is the dissolved carbon dioxide gas in water, which acts as a source of food for water plants. The water plants convert the carbon dioxide gas into their food with the help of chlorophyll and sunlight.

Thus, the materials can be classified on the basis of their solubility in water.

4.0Objects May Float or Sink in Water

The substances like sand and chalk powder sink in water, whereas materials like coconut oil and kerosene oil float on the surface of water.

It is because the substances heavier than water sink in it. Whereas the substances lighter than water, float in it. Thus, we can group materials on the basis of sinking or floating in water. 

(a) Stone, key, coin, and the brass screw sink in water. Thus, they can be grouped as substances heavier than water.

(b) Wax, plastic ball, wood, leaf, and ice float on the surface of water. Thus, they can be grouped as substances lighter than water.

5.0Transparency

Transparency is another property of materials which is used to distinguish them.

(a) Look through the clear glass window pane of your bedroom. You will be able to see things clearly outside your bedroom, in spite of the fact that there is solid glass in between you and outside. Such materials through which you can see are called transparent materials.

(b) Now place a white sheet of paper on the glass window pane and look through it. You will notice that you cannot see anything through paper. Such materials through which you cannot see are called opaque materials.

(c) Now remove the paper and in the middle of it. Pour a few drops of any kind of oil. When the oil spreads on the paper, place it on the glass window pane and look through it. You will notice that the objects outside are faintly visible. Such materials, through which you can see partially, are called translucent materials. 

Transparent: A material through which you can see clearly is called transparent material. It happens so because light can pass through it. 

Transparency: The property of a material through which you can see clearly is called transparency.

For example, 

Keeping eatables in transparent jars, makes it easy to see them

(i) Solids such as glass, diamond, gems and certain kinds of plastics are transparent materials. 

(ii) Most of the liquids, such as water, kerosene oil, alcohol, sea water, etc., are transparent materials.

(iii) All gases, such as oxygen, hydrogen, nitrogen, air, etc. are transparent materials.

Opaque: A material through which you cannot see is called opaque material. Through it light cannot pass. 

For example,

Solids, such as metals (all kinds), wood, paper, stones, etc, are opaque materials. 

Opacity: The property of materials through which you cannot see is called opacity.

Translucent: A material through which you can see partially is called translucent material. Light can pass through it but we cannot see clearly through it.

For example,

Ground glass, frosted glass, tissue paper, butter paper, oiled paper, muddy water, fog, mist, dust laden air are translucent materials.

Thus, on the basis of seeing through a particular material, the substances can be grouped as transparent, opaque and translucent.

6.0Conductivity

Conductors: Conductors are the materials or substances which allow electricity to flow through them. They conduct electricity because they allow electrons to flow easily inside them from atom to atom. Also, conductors allow the transmission of heat or light from one source to another.

Metals, humans, earth, and animals are all conductors. This is the reason we get electric shocks! Moreover, the human body is a good conductor. So it provides a resistance-free path for the current to flow from wire to body.

Conductors have free electrons on its surface which allow current to pass through easily. This is the reason why conductors are able to conduct electricity.

Electrons: An electron is a charge particle it is negatively charged sub atomic particle.

Examples of Conductors

• Material such as silver is the best conductor of electricity. But, it is costly and so, we don’t use silver in industries and transmission of electricity.

• Copper, Brass, Steel, Gold, and Aluminium are good conductors of electricity. We use them in electric circuits and systems in the form of wires.

• Mercury is an excellent liquid conductor. Thus, this material finds use in many instruments.

• Gases are not good conductors of electricity because the atoms are quite far away. Thus, they are unable to conduct electrons.

Insulators: Insulators are the materials or substances which resist or don’t allow the current to flow through them. In general, they are solid in nature. Also, insulators are finding use in a variety of systems. As they do not allow the flow of heat. The property which makes insulators different from conductors is its resistivity.

Wood, cloth, glass, mica, and quartz are some good examples of insulators. Also, insulators are protectors. They give protection against heat, sound and of course passage of electricity. Furthermore, insulators don’t have any free electrons. It is the main reason why they don’t conduct electricity.

Examples of Insulators

• Glass is the best insulator as it has the highest resistivity.

• Plastic is a good insulator and it finds its use in making a number of things.

• Rubber is a common material used in making tyres, fire-resistant clothes and slippers.

This is because it is a very good insulator.

7.0Malleability, Ductility, Brittleness

Malleability is a physical property of metals that defines their ability to be hammered, pressed, or rolled into thin sheets without breaking. In other words, it is the property of a metal to deform under compression and take on a new shape.

The physical property of a metal that can be drawn into the thin wire is called ductility or ductility is the property of metal associated with the ability to be hammered thin or stretched into wire without breaking. The non-metals are generally not rolled into wires because they are formed of weak attractive forces and thus can be easily broken if any external force is applied. This property is not brittle.

8.0Also Read