Lesson Notes By Weeks and Term v5 - Grade 4

Lesson Video

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Performance objectives

• Identify properties like hardness, flexibility, strength, and absorbency.
• Observe how heating and cooling change materials.
• Compare and classify materials based on their properties.
• Explain why a material is good for a specific purpose.
• Conduct simple experiments to test material properties.

Lesson summary

This week, we delve deeper into the fascinating world of matter and materials! We've already learned that everything around us is made of matter, and that matter exists in different states: solid, liquid, and gas. But how do we describe these materials? What makes wood different from water, or metal different from air? Understanding the properties of materials is crucial in South Africa because it helps us choose the right materials for building houses, making tools, growing food, and even recycling waste responsibly. For instance, knowing that corrugated iron is strong and waterproof helps us understand why it’s used so often for roofing, especially in areas with heavy rainfall.

Lesson notes

Properties of Materials: Properties are characteristics that help us describe and identify materials. Think of them as clues that tell us what a material is like.

Hardness: Hardness describes how easily a material can be scratched. A hard material is difficult to scratch. Diamond is a very hard material. Think about the surface of a rock versus the surface of butter. Which one is easier to scratch? The rock is harder than the butter.

Flexibility: Flexibility describes how easily a material can be bent without breaking. A flexible material can be bent easily. Think about a rubber band versus a wooden ruler. Which one is more flexible? The rubber band is more flexible.

Strength: Strength describes how well a material can resist being broken or torn. A strong material can withstand a lot of force. Think about a steel beam versus a piece of paper. Which one is stronger? The steel beam is stronger. A building needs strong materials like bricks and steel to prevent it from collapsing.

Absorbency: Absorbency describes how well a material can soak up liquids. An absorbent material soaks up liquids easily. Think about a sponge versus a plastic bag. Which one is more absorbent? The sponge is more absorbent. Towels are made of absorbent materials because they need to soak up water. Examples of materials and their properties: | Material | Hardness | Flexibility | Strength | Absorbency | Common Uses | | ----------------- | -------- | ----------- | -------- | ----------- | ---------------------------------------------------------------------------------------------------------------------------------------- | | Wood | Medium | Medium | Medium | Low | Building houses (especially in rural areas), making furniture, firewood, pencils. | | Metal (Steel) | High | Low | High | Low | Building bridges and tall buildings, making cars, pots and pans, knives, and tools. | | Plastic | Low-High | Medium | Medium | Low | Making bottles, toys, packaging, pipes, furniture (depending on the type of plastic). Contributes to pollution in South Africa if not recycled. | | Cloth (Cotton) | Low | High | Low | High | Making clothes, towels, bedsheets, bandages. | | Glass | High | Low | Medium | Low | Making windows, bottles, glasses, mirrors. Can be recycled in South Africa. | | Rubber | Medium | High | Medium | Low | Making tyres, erasers, gloves, waterproof clothing. | Heating and Cooling Materials: Heating and cooling can change the properties and even the state of matter.

Heating: Heating a solid can make it melt into a liquid (like ice melting into water). Heating a liquid can make it evaporate into a gas (like water boiling into steam). Heating some materials can also change their properties without changing their state. For example, heating clay makes it hard and durable, which is why it's used to make bricks.

Cooling: Cooling a gas can make it condense into a liquid (like water vapour turning into rain). Cooling a liquid can make it freeze into a solid (like water freezing into ice). Cooling can also change the properties of materials. For example, cooling candle wax makes it solid and hard.

Worked example

Example 1: Identifying properties of a brick.

A brick is used to build walls. What properties make it suitable for this purpose?

Solution: A brick is hard (difficult to scratch), strong (can support weight), and not very absorbent (doesn't soak up water easily). The strength allows it to support the weight of the wall, the hardness makes it durable, and the low absorbency protects the wall from rain damage.

Example 2: Predicting changes when heating butter.

What happens to butter when you leave it out of the fridge on a hot day?

Solution: Butter will soften and eventually melt. This is because heat increases the movement of the particles in the butter, causing it to change from a solid to a liquid.

Example 3: Choosing the right material for a raincoat.

You need to make a raincoat. Which property is most important for the material you choose?

Solution: Absorbency. You need a material that is not absorbent, so water rolls off it instead of soaking in. Materials like plastic or specially treated fabrics are suitable because they are waterproof (low absorbency).

Guided Practice (With Solutions)

Question 1: Which of the following materials is the most flexible: a rock, a piece of paper, or a rubber band? Explain your answer.

Solution: A rubber band is the most flexible. Flexibility means how easily something can be bent without breaking. A rubber band can be stretched and bent easily without breaking, whereas a rock and a piece of paper will break or tear if bent too much.

Question 2: You want to build a bridge across a river. Which property is most important for the material you choose: hardness, strength, or absorbency? Explain why.