Lesson Notes By Weeks and Term v5 - Grade 4

Lesson Video

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Performance objectives

• Define what a structure is.
• Explain what 'strength' and 'stability' mean.
• Identify factors that make a structure strong.
• Describe how shape affects a structure's strength.

Lesson summary

Structures are all around us, from the houses we live in to the bridges we cross. Understanding how structures are built to be strong and stable is incredibly important. Without strong and stable structures, buildings could collapse, bridges could fall, and even furniture could break easily. Think about the houses in your community – they need to withstand strong winds, heavy rain, and sometimes even earthquakes! Knowing about strong and stable structures helps us to build safer homes, schools, and communities for everyone in South Africa. This week, we will investigate what makes a structure strong and stable.

Lesson notes

What is a Structure? A structure is something that is built or constructed with a definite size and shape and for a specific purpose. Structures can be natural (like a tree or a spider web) or man-made (like a house or a bridge). They are designed to support a load or weight.

Examples we see every day include: Buildings: Houses, schools, shops, hospitals, etc.

Bridges: Used to cross rivers, valleys, or roads.

Furniture: Tables, chairs, beds, cupboards, etc.

Towers: Cell phone towers, water towers, observation towers. Strength vs.

Stability Strength: A structure's ability to withstand forces without breaking or collapsing. A strong structure can hold a large weight or resist being bent or broken. Think of a strong brick wall that can support the roof of a house.

Stability: A structure's ability to remain upright and not fall over. A stable structure is balanced and can resist being toppled by forces like wind or pushing. Think of a wide-based table that is less likely to tip over than a tall, thin one.

Factors Affecting Strength and Stability: Several factors influence how strong and stable a structure is: Materials: The type of material used to build a structure is crucial. Some materials are stronger than others. For example, steel is much stronger than cardboard.

Shape: The shape of a structure and its components can significantly affect its strength and stability. Certain shapes are naturally stronger.

Base: A wider base generally provides more stability. A structure with a narrow base is more likely to tip over.

Connections: How the different parts of a structure are joined together is important. Weak connections can cause a structure to collapse, even if the materials themselves are strong.

Load: The amount of weight or force a structure needs to support. A structure needs to be strong enough to handle the load it is designed for.

Shapes and Strength: Triangles: Triangles are incredibly strong shapes. When pressure is applied to a triangle, the forces are distributed along all three sides, making it very resistant to bending or breaking. This is why you see triangles used in bridges and roof supports.

Arches: Arches are also strong shapes. They distribute weight outwards and downwards, which allows them to support heavy loads. Bridges often use arches.

Cylinders: Cylinders are strong because they distribute weight evenly around the structure. Think of the cardboard tube inside a roll of paper towels - it can withstand significant pressure.

Worked example

Example 1: Comparing Materials

Imagine you want to build a small house for your pet tortoise.

Which material would be better: cardboard or bricks? Why?

Answer: Bricks would be a better choice. Bricks are much stronger than cardboard and can withstand rain and pressure better. Cardboard would easily get wet and collapse under even a small amount of weight.

Example 2: The Importance of a Wide Base

Why is it important for the legs of a table to be spread out rather than close together?

Answer: Spreading the legs of a table further apart creates a wider base. A wider base makes the table more stable because it is harder to tip over. If the legs were close together, the table would have a narrow base and would be very unstable.