Standard Science Primary 4 Energy

Jun Jie could not unscrew the metal lid of a glass jar. He ran hot water over the metal lid for a minute and then was able to open it easily. Why?

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

Worked Solution

Step 1: The metal lid gains heat from the hot water. Step 2: Metals expand when they gain heat. Step 3: The expansion makes the lid slightly larger/looser, making it easier to unscrew.

Correct answer: The metal lid expanded.

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