- Students need to be familiar with various properties of a material for Primary School Leaving Examination Science, namely strength, flexibility, buoyancy, waterproofness, and transparency
- These properties of materials are often confused with one another: a) Hardness (involve scratch tests) and strength (how much force is applied before a material breaks), b) Strength and flexibility (how much a material can bend before it breaks), c) Flexibility and elasticity (how much a material can be stretched and return to its original shape and size)
- Umbrellas need to be waterproof so that the person using it will not get wet.
- A chair must be able to support heavy weights so that it will not break easily when a heavy person sits on it.
- When ice freezes, its volume increases. This makes ice less dense than water, which is why ice floats on water. This is why glass is not used when freezing water, because the increased volume may cause the glass to break.
- Copper is used to make a kettle because it is a very good conductor of heat and cheaper than silver and gold.
- Wires are usually made of copper as it is a good conductor of electricity and is cheap.
- Aluminium is used to make one yen coins in Japan because it is very light.
- Silver can prevent the growth of bacteria. People long ago stored milk products in silver containers. Milk products that were stored in silver containers last longer.
- Tungsten is used as the filament of a light bulb because it is a conductor of electricity. As it has very high resistance, it converts most of the electricity passing through it to heat and light energy, allowing some electricity to pass through.
- The rubber float is inflated, meaning it contains air, which makes it less dense than water. This lower density allows it to float. On the other hand, the eraser is solid rubber and denser than water, causing it to sink. The difference in density between the two objects explains why the rubber float will float while the eraser will sink.
- Cork is a good insulator of heat, so it protects the surface beneath the coaster from being burnt by the heat from the pot.
- Rubber provides good friction between the tyres and the road.
- Aluminium is strong and light, so it’s suitable as the bicycle frame.
Flexibility
- Questions on flexibility seem to be popular among Science teachers, as illustrated by the following questions
-
String is made of flexible material and bend downwards
-
Material S, because it is the most flexible. The hose needs to be flexible so that it can be coiled up when not in use.
-
Bubble wrap is flexible and can cushion the fragile items.
Waterproof
- I was impressed that the examiners tested the concept of “water is a better conductor of heat than air” for the following question.
-
Material A is waterproof as it doesn't allow water to pass through. Material B allows most water to pass through, Material C is most absorbent.
-
Container C. Since Material C absorbs the most water and is the wettest, the water in the material gains heat the fastest from the hot water in the container to evaporate into water vapour, causing the hot water to lost heat the fastest and be at the lowest temperature after 3 minutes.