✔ 最佳答案
When the test tube is heated, the temperature of the glass of the test tube is high.
When the heated test tube is put into water, the temperature of outer wall of the test tube drops suddenly. The outer wall of the test tube thus sharply contracts due to the sharp decrease in temperature. However, the inner wall of test tube remains at high temperature and its contraction is insignificant. The great difference in contraction between the inner wall and outer wall of the test tube exerts a force on the glass and consequently cracks the test tube.
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