Standard Science Primary 4 Energy

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

A The metal lid expanded more than the glass jar.
B The glass jar contracted in hot water.
C The hot water acted as a lubricant.
D The hot water made the metal lid softer.
Show Worked Solution

Worked Solution

Step 1: Metals are good conductors and expand when heated. Step 2: The lid expands more than the glass neck. Step 3: This makes the fit looser, allowing it to be unscrewed.

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

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