Choosing Materials for a Cooking Pot Handle and Drinking-Water Storage
In the school kitchen, the handle of the large cooking pot has broken. The cook needs a new handle that will not burn her hand when the pot is over a hot fire. The school has four materials: a strip of hardwood, a piece of aluminium from an old roof sheet, a plastic strip cut from a bucket, and a piece of cloth. The pot is 30 cm deep and the handle will be fixed 5 cm from the top edge, directly above the fire. The cook also needs a container to store drinking water for 40 learners. There is a metal drum that leaks at a seam, a clean plastic barrel with a lid, and a clay pot that is cracked. The teacher asks pupils to choose materials and justify their choices using properties, not cost alone.
1. Choose the best material for the pot handle and explain why the other three materials are unsafe or unsuitable.
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Hardwood is the best handle among the four. Wood is a poor conductor of heat, so heat from the pot travels slowly along it and the cook's hand is protected. It is also strong enough and does not melt. Aluminium is a good conductor, so the handle would become hot and burn the cook. Plastic from a bucket softens or melts near a hot fire and may catch fire, so it is unsafe only 5 cm above the fire. Cloth is a poor conductor but it is not rigid, can catch fire, and would soon char. The handle should be long enough to keep the hand away from the flame, and it should be fixed firmly. Cost matters, but safety and properties come first.
2. Which container should be used to store drinking water, and why are the other two containers not acceptable?
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The clean plastic barrel with a lid is the best choice. Plastic does not rust, is light, and a lid keeps out dirt, insects and sunlight that can grow algae. The metal drum leaks at a seam; even if repaired, it may rust and the seam may fail again, and without a lid the water can be contaminated. The cracked clay pot will leak and cannot be cleaned properly. The barrel should be washed, kept in the shade, and the water should be treated or boiled before drinking if it is not from a safe supply. Choosing a container is not only about holding water; it is about keeping it safe to drink.
3. A metal spoon left in hot porridge becomes hot, but a wooden spoon does not. Explain this using the idea of heat transfer, and link it to the choice of pot body and handle.
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In the hot porridge, the particles in the metal spoon gain energy and vibrate faster. Metal has particles close together and free electrons that transfer energy quickly, so heat travels up the spoon to the hand. Wood is a poor conductor: its particles transfer energy slowly, so the wooden spoon stays cooler. This is why a metal spoon feels hot and a wooden one does not, even when both are in the same porridge. The same idea explains why the pot body is metal, to conduct heat to the food, while the handle should be wood, to slow heat transfer to the hand.