All the objects around us are made of something. They look different, they are different on touch, they behave differently. Let's take some objects in our hands and make a small observation. We will try to find some differences between them. For instance, let's take for observation a pillow and a pen. What can we tell about each of them? The pillow is soft, you can easily squeeze it; it is smooth, and not so heavy. Now, take the pen. It is lighter than the pillow. It is hard, you can not easily squeeze it, or if you try to squeeze it harder, you might break it. Can you break the pillow if you squeeze it? Well no. So, why these objects are so different? It is because they are made up of different materials.
Actually, all objects can be made up of many different materials.
What does this mean? For example, the table can be made of wood, so wood is the material. But the same object (the table) can be made up of other materials, like plastic or metal. Or the windows are made up of glass, so the material that is used to make windows is glass.
If we continue to observe, we can conclude that objects have many differences, some of the objects are soft, some are hard, some breakable, some heavy, or some objects are transparent, some of them are shiny...we can continue this list a lot.
In this lesson, we are going to learn about MATERIALS, and we will discuss:
- What are materials?
- Examples of materials.
- Natural VS Man-made materials.
- How are materials grouped?
- Properties of materials.
What are materials?
From the above, we can conclude that material is a substance or mixture of substances that constitute an object. Examples of materials include wood, glass, plastic, metals, paper, rubber, leather, cotton, silk, sand, sugar, wool, and so on.
Objects can be made up of one material. For example, the notebook, which is made up of paper. Or a wooden table, made up only of wood.
Objects can be made up of a combination of two or more materials. The pen is made up of metal, plastic, and ink.
One material could be used for making many different objects:
| MATERIAL |
OBJECTS |
| wood |
tables, chairs, doors, yard fences, house floor |
| paper |
books, notebooks, newspaper, boxes, food packages |
| cotton |
clothes, blankets, towels, curtains |
| glass |
windows, drinking glasses, cups, bowls |
| plastic |
bottles, containers, toys, helmets |
| rubber |
tires, balloons, rubber boots |
| leather |
footwear, automobile seats, clothing, bags, sofas |
| metal |
jewelry, cutlery, wires, building constructions |
These lists can be much longer.
Natural VS Man-made materials
All the materials that we use to make objects can be natural or man-made.
Natural materials are found naturally on our planet. They come from our Earth directly (from its plants and animals). They include water, wood, silk, wool, gold, rocks, minerals, leather, cotton, copper, iron, etc.
Man-made materials, unlike natural materials, are a type of materials that don't occur naturally and are made by humans. Man-man materials include glass, plastic, cement, paper, sugar, etc.
Groups of materials
To better understand, materials are generally divided into four main groups. They are:
- Metals, which are composed of one or more metallic elements, such as iron, copper, titanium, nickel, gold, and so on, and nonmetallic elements (carbon, nitrogen, oxygen) in small amounts;
- Polymers, which are materials made of long, repeating chains of molecules. They have unique properties, depending on the type of molecules being bonded and how they are bonded. Polymers include rubber and plastic materials. Nylon, polyester, Teflon, silicone, belong to this group. Also, cotton, wool, and silk.
- Ceramics, which are inorganic non-metallic solids, made up of either metal or non-metal compounds that have been shaped and then hardened by heating to high temperatures. Clay, bricks, tiles, glass, and cement are probably the best-known examples.
- Composites, which are a combination of two materials with different physical and chemical properties. When they are combined they create a material that is specialized to do a certain job, for example, to become stronger, lighter, or resistant to electricity.
Properties of materials
The following are the properties of materials.
- Roughness or smoothness. Rough materials have an irregular and uneven surface, with bumps or ridges, and are not smooth to touch. Like the asphalt. Materials having smoothness on their surface are smooth materials. Silk, glass, metals are examples of smooth materials.
- Hardness or softness. Those materials which cannot be easily compressed, cut, bent, or scratched are called hard materials. Examples: Iron, glass. Those materials which can be easily compressed, cut, bent, or scratched are called soft materials. Cotton fabric and wool are examples of soft materials.
- Transparency, translucency, or opaqueness. Materials like air, water, and clear glass are called transparent. When light encounters transparent materials, almost all of it passes directly through them. Materials like frosted glass and some plastics are called translucent. These materials allow some light to travel through them. Wood, stone, ceramic are common examples of opaque materials, and they are the most common type of material. These objects allow no light to pass through them.
- Physical state (solid, liquid, or gas). Materials depending on their state of matter can be solids, liquids, or gas.
- Appearance (lustrous or non-lustrous). Lustrous materials are those materials that have shiny surfaces. Lustrous materials include metals like silver, gold, copper, iron. Non-lustrous materials are those materials that do not have shine on their surfaces. Non-lustrous materials include wood, clay, cotton, etc.
- Solubility or insolubility in water. Soluble materials are those that easily dissolve in water, and include sugar, salt. Insoluble materials do not dissolve in water. Examples are wood, plastic, cotton, etc.
- Heaviness or lightness with respect to water. Materials that are lighter than water are wood, ice, oil. Materials heavier than water are stone, soil.
- Attraction towards a magnet. Iron, nickel and cobalt are examples of magnetic materials (that are attracted by a magnet). Wood, glass, plastic, paper, copper, cotton, water are not attracted by a magnet. They are nonmagnetic materials.
- Conduction of heat. The different materials conduct heat at different rates: metals conduct heat the fastest, wood and plastic much slower.
- Conduction of electricity. Materials made of metal are common electrical conductors (they allow the flow of charge, electrical current, in one or more directions). Materials that do not let current flow easily are called insulators. Most nonmetal materials such as plastic, wood, and rubber are insulators.
Which material will be used for making objects, depends on its properties, mentioned above.
Objects have different purposes. The properties of the materials help to serve their purpose. Let's understand this.
The window's purpose is to let the sun shines inside our room, to bring light inside, but they should protect us from cold, wind, or rain, right?
That is why the windows are made up of glass, which is a hard and transparent material. Imagine a window made up of paper. Would it protect our house from cold or rain? Would it let the sun shines to lighten our room? Well, no. That is what is meant when we say that objects must be made of suitable material, and materials help objects to serve their purpose.
Or, could you eat with the fork if it is not made of hard materials like metal or plastic? Of course not. Imagine a fork made up of cotton.
Would people use plastic to make magnets? Of course not, magnets should be made up of a magnetic material.
Or, can the tires of our car be made up of wood? Rubber tires should be made of rubber because it is a flexible material and will be smooth when going over small pebbles and rocks.
Or our shoes of glass? Shoes shouldn't be made up of glass because it is hard and easily breakable.
That is why for making certain objects are used materials with respect to their properties.
Summary:
- All objects can be made up of many different materials.
- Examples of materials include wood, glass, plastic, metals, paper, rubber, leather, cotton, silk, sand, sugar, wool, and so on.
- Objects can be made up of one material, or of a combination of two or more materials.
- One material could be used for making many different objects.
- All the materials that we use to make objects can be natural or man-made.
- Materials are generally split into four main groups: metals, polymers, ceramics, and composites.
- Materials have different properties.
- Objects have different purposes. The properties of the materials help to serve their purpose.
