A thermometer is placed in water in order to measure the water’s temperature. What would cause the liquid in the thermometer to drop?

The thermometer’s liquid drops when it cools and contracts. If the water’s molecules lose kinetic energy, the water’s temperature decreases, and heat flows from the thermometer’s liquid to the cooler water. The thermometer liquid then contracts, so its level falls. Therefore, the correct choice is “The kinetic energy of the water molecules decreases.”

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