Heat or thermal energy as understood is some kind of vibrations of molecules / atoms of the matter. If the molecules are tightly bound in case of solids, it is to-and-fro motion what we call vibration, or, it may be random motion of molecules in case of liquids/gases/plasma.
Sound, being waves, is also a vibration of matter. Why, then, if we heat one end of a solid rod, assuming rod is at least few feet in length, does it take ages for the heat to reach the other end, whereas sound reaches in no time ? (sound travels at 1400 m/s approx in solid)
Doesn't it show that heat is more an intra-atomic feature rather than an atomic or molecular motion? Given the fact that electrical good conductors are also good conductors for heat, can we assume that heat is chaotic motion of electrons (the "electron gas") or some other sub-atomic particle? The model should be correlated or validated for all the phenomena that involve heat, some of them listed below:
- Solid melts as it is heated, liquid vaporizes when heated.
- Hot material emits light (frequency of which depends upon temperature)
- Light is absorbed converting to heat.
- Microwave produces enormous heating in certain material (eg. a pan of water in a microwave oven)
- Throttling of a gas through a nozzle produces cooling (or absorbs heat)
- Mechanical friction produces heating
- Compression of gas produces heat
- Heating causes expansion in solid, liquid and gas (though mechanism may differ among the 3 states)
- Heat diff can produce an EMF and vice-versa in a thermocouple (Seebeck / Peltier effect)
- Expansion of rubber band produces heat, contraction absorbs heat
- Passage of electric current through metal produces heat
- Magnetic hysteresis produces heat
- Sound and other mechanical motions dissipates into heat
- Certain chemical reactions (exothermic) produce heat , whereas some (endothermic) absorbs it.
- Change of the state of matter produces/absorbs heat without raising the temperature (latent heat of fusion , latent heat of vaporization)