Microscopic Interpretation of Temperature

Fig. 2-1 In a solid, the molecules are bond together as if they are connected by springs. The molecules are in random vibration and the temperature of the solid is a measure of the average kinetic energy of the molecules. Fig. 2-2 The gas molecules in a container are in rapid random motion. The temperature of the gas is a measure of the average kinetic energy of the molecules.

Matters are made up of atoms or molecules. These particles are in random motion and exert force on one another. Thus the particles have the kinetic energy of the random motion as well as the potential energy from the interactive force. When an object warms up, its particles speed up and vibrate more rapidly. When it cools, the particles slow down. In fact,

the temperature of a body is a measure of the average kinetic energy of its particles

Note that the temperature depends on the average kinetic energy, but not the total kinetic energy, of the particles. In other words, temperature actually measures the average value of the kinetic energy carried by each particle in the object.

 
  Fig. 2-3 The Kelvin temperature scale.

The average kinetic energy of the particles has a minimum possible value. This implies that an object cannot be cooled indefinitely. The temperature -273 is the lowest possible temperature in the universe and is called the absolute zero. Nothing can be cooled below this temperature. The absolute zero defines the zero temperature (0 ) in the Kelvin temperature scale. One degree Kelvin is equivalent to one degree Celsius. The two scales can be inter-converted as follows:

Temperature in = Temperature in + 273

Kelvin scale is also known as the absolute temperature scale.

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