Exercises: Properties of materials

Match each property with its definition: (a) hardness, (b) elasticity, (c) electrical conductivity, (d) density. Definitions: 1. ability to regain shape after being deformed; 2. resistance to being scratched or worn away; 3. ease of allowing electrical current to pass through; 4. ratio between the mass of a material and the volume it occupies.

Sensory properties are perceived through the senses. Describe the color, luster and texture of three objects in your classroom (the desk, a ruler, the whiteboard) and explain which sense you use to identify each of those properties.

True or false? Justify each answer: (a) copper is a good electrical conductor; (b) rubber is a very hard material; (c) a piece of steel weighs more than a piece of cork of the same size because it is denser; (d) glass is an elastic material.

Which property matters most in each case? (a) a saw blade; (b) the inside of a cable; (c) a ballpoint pen spring; (d) the filling of a winter coat. Justify each answer with one sentence.

The figure shows a hardness scale with several materials ordered from softest to hardest, but one of them has lost its name, as shown in the diagram.

Which material that you know could fill the gap? Reason your answer by comparing it with its neighbors on the scale, and then place two other materials on the scale: your fingernail and diamond.

Classify these materials into electrical conductors and insulators: copper, plastic, dry wood, steel, rubber. Explain why this property determines which material goes inside and which goes outside a cable.

An elastic band and a piece of plasticine deform when stretched, but only one of them regains its shape when released. Explain which property differentiates them and give an example of an object in which this property is essential for it to function.

Cooking pots are made of metal, but the handle is usually made of wood or plastic. Explain this using thermal conductivity and reason what would happen with a pot made of a single piece of steel, handle included.

The figure compares several properties of five workshop materials, but some cells are incomplete, as shown in the diagram.

Complete the boxes marked with '?' and then explain which material from the table you would choose to manufacture a hammer head and which for the flexible handle of a toy whip, reasoning the properties that made you decide.

A copper coin scratches plaster, but does not scratch steel; a fingernail scratches plaster, but does not scratch the coin. Order these four materials from least to most hard and explain what simple test you have used to order them (the "scratch test").

A cork cube and a steel cube of the same size do not weigh the same. Explain which property accounts for this, reason why cork floats in water and steel sinks, and what the density of water has to do with it.

Choose the material for each part of an umbrella from these options and justify each choice with at least one property: (a) the ribs: flexible fiber or a cookie; (b) the canopy: waterproof fabric or newspaper; (c) the handle: hard plastic or sponge.

A cell phone casing can be made of plastic or metal. Compare both options considering weight, scratch resistance, and how well they transmit Wi-Fi signals, and state which one you would choose with your reasons.

Classify these properties into mechanical, thermal, electrical or sensory: hardness, thermal conductivity, luster, elasticity, electrical conductivity, color. Then give an example of an object in which each one is the key property.

An electrical cable is copper on the inside and plastic on the outside. Explain what property each layer provides and reason what could happen if the cable gets stripped and the copper is exposed.

Glass is very hard (it hardly scratches at all), but it breaks if dropped on the floor. Explain the difference between hardness and brittleness using this example, and name another hard and brittle material, as well as one that is soft but hard to break.

The school wants to buy new chairs for the classroom. Prioritise the three most important properties (strength, light weight so they can be moved easily, ease of cleaning, comfort, etc.), choose one material for the frame and another for the seat, and explain which materials you rule out and why.

Design a workshop experiment to order three materials (pine wood, aluminum and a stone) by hardness, using only the materials themselves to scratch each other. Explain the procedure, what you would record in each test, and what conclusion you expect to get.

A shop sells steel, aluminum and carbon fiber bicycles. Compare the weight, strength and price of each option and recommend one for: (a) a person who uses it daily to go to school; (b) a competitive cyclist. Justify why your recommendations are different.

A copper saucepan with a wooden handle costs considerably more than one made entirely of steel. Analyse which properties explain this design (copper spreads heat very evenly, wood hardly heats up) and reason whether the extra cost is worth it for cooking on a low heat.

'The harder a material is, the better it is for everything.' Evaluate this statement using two counterexamples (a tyre's rubber, a soft phone case, the sole of a shoe) and rephrase it so that it is correct.

You are going to choose the material for a reusable bottle: stainless steel, hard plastic or glass. Create a decision matrix with four criteria (weight, drop resistance, hygiene and taste, price), score each material from 1 to 3, and draw a reasoned conclusion from your table.

You can do it on paper and send a photo with your answer.

You are given a mystery object: it shines like a metal, is quite heavy, cannot be scratched with a fingernail, and is not attracted by a magnet. Reason what material it could be (stainless steel? aluminum? ceramic?) and design two more tests to find out without breaking it.

Design a test to compare the elasticity of three rubber bands of different thicknesses: what you would measure (how much each stretches when hanging the same weight and whether it returns to its original length when the weight is removed), how you would record it, and what you predict will happen. Explain exactly what property you are measuring and how it differs from hardness.