4. Your older brother announces that the lid to a jar of pickles from the refrigerator

is "impossible" to loosen. You take the jar, hold the lid under the hot water from

your sink's faucet for a few seconds, and calmly open the jar. Your brother, when

faced with this blow to his pride, claims that he loosened it for you. What

knowledge of materials have you applied in this situation that really explains

how you were able to open the lid?