What is temperature?

[Lowemack]

If temperature is - "The measure of the average kinetic energy of the particles in a substance", then how does an atom "absorb" infra red radiation and thus increase its speed.

 

And more to the point, how, when radiating(cooling down), does an atom know which way to emit the radiation to slow it down?

 

If the temperature of an atom is a meassure of its speed then is temerature relative?

 

Please help!!

[timo]

Temperature is a statistical variable, namely a parameter in the energy distribution. The reason why it´s often called a measure of the average kinetic energy of the particles in a substance is that Thermodynamics is often (especially in introductionary courses) done on systems whose "only energy" is kinetic one. Due to being a statistical approach, the whole concept of thermodynamics can usually only be applied to a large number of particles and not to individual particles or small numbers of them. Therefore, one usually cannot consistently speak about the temperature of an individual atom.

 

Normally, temperature will decrease if the average energy of the system´s particles dereases and increase if the average energy increases. Therefore, absorbing energy which increases the total energy and thus also the average energy of the system will usually increase temperature. Same goes for giving away energy like by emitting a photon (where it´s loweing the temp, of course).

[DV8 2XL]

The temperature of an object depends on how fast the atoms and molecules which make up the object can shake, or oscillate. As an object is heated, the oscillations of its atoms and molecules speed up; as an object is cooled, the oscillations of its atoms and molecules slow down.

 

More quantitatively, the order of magnitude of the fluctuations of the energy associated with an atom, molecule or another elementary constituent of a physical system is kBT, where kB is Boltzmann's constant, (1.380 6505(24) × 10−23 J/K) and T is temperature, expressed in Kelvins.

 

A system doesn't "know" which way to radiate a photon; it does so at random.

 

And temperature is relative only to Absolute Zero