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Materials and Matter - Testing materials for specific uses

Grade 3Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Materials possess specific physical properties such as being waterproofwaterproof (repelling water), absorbentabsorbent (soaking up water), flexibleflexible (bends easily), or rigidrigid (does not bend).

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When testing materials, we must conduct a 'fair test.' This means keeping all variables constant except for the material being tested. For example, using the same amount of water, measured in mlml, to test different fabrics.

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The suitability of a material depends on its properties. For example, a bridge needs a material with high tensilestrengthtensile strength, while a towel needs high absorbencyabsorbency.

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Matter is made of tiny particles. In solids, these particles are packed tightly together, giving the material its densitydensity and shape.

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Transparency refers to how much light passes through a material. TransparentTransparent materials allow all light through, while opaqueopaque materials block light entirely.

📐Formulae

Density(ρ)=Mass(m)Volume(V)\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}

Total Mass=mmaterial+mabsorbed_liquid\text{Total Mass} = m_{material} + m_{absorbed\_liquid}

Percentage of Water Absorbed=Mass of water absorbedOriginal mass of material×100\text{Percentage of Water Absorbed} = \frac{\text{Mass of water absorbed}}{\text{Original mass of material}} \times 100

💡Examples

Problem 1:

A student wants to test which material is best for a raincoat. They have samples of Cotton, Plastic, and Wool. They pour 50 ml50\text{ ml} of H2OH_2O on each. Which property are they testing?

Solution:

WaterproofWaterproof property (Permeability).

Explanation:

To be suitable for a raincoat, a material must be waterproof. If the 50 ml50\text{ ml} of water passes through the material, it is permeablepermeable and unsuitable. If the water stays on top or slides off, the material is waterproofwaterproof.

Problem 2:

Calculate the density of a metal block used for building a structure if its mass m=200 gm = 200\text{ g} and its volume V=40 cm3V = 40\text{ cm}^3.

Solution:

ρ=5 g/cm3\rho = 5\text{ g/cm}^3

Explanation:

Using the formula ρ=mV\rho = \frac{m}{V}, we substitute the values: ρ=20040=5 g/cm3\rho = \frac{200}{40} = 5\text{ g/cm}^3. This helps engineers decide if the material is too heavy for a specific use.

Problem 3:

Why is copper (CuCu) used for electrical wires instead of plastic?

Solution:

Electrical Conductivity.

Explanation:

Copper is a conductorconductor, meaning it allows electricity to flow through it easily. Plastic is an insulatorinsulator and is used to wrap the wires to keep us safe from the electric current.