Answer to Question #118597 in Physics for Susan Williams

Question

Distinguish between heat and temperature. Give reasons why mercury is preferred to water as a thermometric liquid

Answer 1

Heat is the total energy of motion of all molecules in a substance. The higher the mass of the substance, the more heat it contains. Temperature is a measure of the speed of molecules in the substance. No matter how large the object is, the temperature does not depend on the size. For instance, in the thermosphere, the temperature reaches 2000 degrees Celsius, but since the density of air is too small, spacecrafts and people cannot notice it. There are too few molecules to provide enough heat. 

We use Mercury in thermometers because it has a high coefficient of thermal expansion, which makes it a perfect medium that we can use to measure temperatures: the higher the temperature, the more mercury expands in size. 

Water, on the other hand, has very little coefficient of thermal expansion and freezes if the temperature is below 0 degrees Celsius.