Standard Science Primary 4 Energy

Jun Jie could not open a metal lid on a glass jar. He poured hot water over the metal lid and was then able to open it easily. Why?

A The metal lid expanded.
B The metal lid contracted.
C The glass jar contracted.
D The hot water acted as a lubricant.
Show Worked Solution

Worked Solution

Step 1: Metals are good conductors of heat and expand when heated. Step 2: Pouring hot water makes the lid gain heat and expand. Step 3: The lid becomes slightly larger and looser, making it easier to unscrew.

Correct answer: The metal lid expanded.

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