Standard Science Primary 4 Energy

Jun Jie found it difficult to open a glass jar with a tight metal lid. He poured hot water over the metal lid and was then able to open it easily. Why?

A The metal lid contracted and became loose.
B The glass jar expanded more than the metal lid.
C The metal lid expanded more than the glass jar.
D The hot water acted as a lubricant.
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Worked Solution

Step 1: Metal is a better conductor of heat and expands faster than glass. Step 2: Hot water causes the metal lid to gain heat and expand. Step 3: This expansion makes the lid larger and looser, making it easier to unscrew.

Correct answer: The metal lid expanded more than the glass jar.

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