Materials - Science Lessons for Grade 4 Students
The objects around us are all made up of different types of materials.
Some examples of materials include plastic, glass, rubber, wood, ceramic, metal and fabric. Simply put, material is what something is made of. A balloon for example, is usually made of rubber. A ruler is usually made of plastic or wood. A comb is usually made of plastic or wood.
Different types of materials have different properties. For example, plastic is different from rubber in many ways. Glass is different from wood in many ways.
Materials can have different colours. For examples, the clothes you wear, made of different types of fabric, come in different colours. Look at the clothes given below. They are all made of one fabric, which is called cotton. The colour of a material is a property that you can observe using your sense of sight.
Texture of a material is how a material feels when you touch it. For example, a cotton shirt feels very different to the touch than a rubber balloon. A plastic comb feels very different when you touch it compared to a piece of paper. Materials can feel hard, soft, rough or smooth. For example, a teddy bear is soft and smooth, but bricks are hard and rough.
A teddy bear
Have you seen safety goggles? The lens of the safety goggles is made of clear plastic. Light is able to pass through the lens easily. A material that allows light to pass through it easily is a transparent material.
However, there are other materials that do not allow any light to pass through it. An example is a sleeping mask. You wear a sleeping mask when you do not want to see any light and so can sleep well. Materials with this property are opaque. We cannot see through opaque materials. Some materials such as wood and metals are always opaque.
A sleeping mask
4. Heat conduction
When a solid object is heated, the heat energy flows from the area that is the hottest to the area that is the coolest. This flow of heat energy is known as conduction.
Some materials such as metals allow heat to flow through them easily. Metals are good conductors of heat.
Other materials such as wood, ceramic and plastic do not allow heat to flow through them easily. They are poor conductors of heat.
You might have experienced this in your day-to-day life. If you use a metallic spoon to stir something hot, the spoon itself gets hot. But if you use a wooden spoon, you can feel that the spoon does not get hot.
Have you seen pots and pans with a metallic part for cooking stuff, and a handle that is made of usually wood? This is because the metal is a good conductor of heat, so cooking will take place. But your hand will not get burnt because you are holding the wooden handle, which is a poor conductor of heat.
A cooking pan with a wooden handle
A magnet is, in simple terms, something that can attract certain other substances.
If an object is attracted by a magnet, we can say that the object is made of magnetic material. Iron and steel are examples of magnetic materials.
A magnet attracting steel clips
Materials that are not attracted by a magnet are called non-magnetic materials. Examples of non-magnetic materials include plastic, glass and wood.
What happens when you add sugar to water and stir it? After some time, you cannot see the sugar. The sugar particles have completely dissolved in water. If a material can dissolve in water completely, it is called a soluble material. Examples for soluble materials are sugar, salt and lemon juice.
However, there are materials that do not dissolve in water. They just float on water or sink into the water. For example, iron rods, oil and kerosene cannot dissolve in water. So they are called insoluble materials.
Another property of a material is whether it floats or sinks in water. If a material is very light, it will float on the surface of the water. For example, a plastic spoon or a dry leaf will float on the surface of the water.
Leaf floating on water
However, if the material is heavy, it will sink in water. For example, if you put a stone into a glass of water, it will sink to the bottom of the glass.