Hardness - Presentation

The presentation on 'Hardness' is designed to explore the concept of hardness in materials and how this property is crucial in determining their practical applications. The lesson sets out to answer three key questions: whether students can create their own hardness scale, link the hardness of materials to their uses, and explain how additives alter the properties of a primary metal. The narrative follows Elsa and Maisie's visit to a local blacksmith, where they learn about the process of making swords in ancient times. The blacksmith illustrates the importance of hardness by explaining how iron, which is relatively soft on its own, was combined with carbon to create hard steel. This process of creating an alloy, which is a mixture of metals that have different properties from the main metal, is further demonstrated with examples such as gold rings, stainless steel, and bronze, highlighting the significance of additives in changing the properties of metals for specific uses.

Further activities within the presentation encourage students to engage with the concept of hardness through various tasks. They are prompted to write a report on the Mohs scale, a tool used by geologists to classify minerals' hardness from 1 (talc) to 10 (diamond). Students also classify items by their hardness using their own scale and test the hardness of different materials, considering why certain materials, like metal for cans or glass for windows, are chosen for specific products due to their properties. In a practical experiment, students make a model alloy and observe how additives affect the properties of the main metal, deepening their understanding of material science. The lesson concludes with a review section, asking students to reflect on what they've learned about hardness, material uses, and the process and purpose of making alloys.