|THERMO Spoken Here! ~ J. Pohl © ~ 2019||www.ThermoSpokenHere.com (C5700-160)|
Science students are physically aware of temperature and the associated event, heat. When heat and temperature are being considered, the model BODY or point mass is inadequate. The new model is substance or material (metal, solid and so). Also a new energy form is introduced: internal energy.
HEAT: Energy transfer between a system and surroundings as a consequence of temperature difference is called heat. The term of our energy equation, Q, represents the sum of all heats of a system event. The sign convention of heat is:
In the absence of all other effects, heat attendant with an
increase of system energy is defined to be positive.
In beginning level thermodynamic analysis, virtually all thermodynamic systems are assumed initially to be in thermal equilibrium with the surroundings. That is, initially 0 = ΣQ. With an event it is common for a substance to experience temperature change. For the case that "some location of the system becomes hotter" (than some temperature of the surroundings) then in time the system temperature (and system energy associated with that temperature) will decrease via heat to the surroundings. That system event is said to be (or to have been) "heat transfer with the surroundings" (or simply "heat".) Heat is difficult to predict and hard to measure even in well-controlled laboratory circumstances.
Thermodynamics and physics texts (sometimes without statement) avoid confrontation with heat by use of one of three stratagems.
We close with a thought puzzle: Does a car overheat or does it under-heat?
Beware of Under-Heating: Automobile operators must be cautious of the level of thermal energy of their operating engines. The machines have schemes to steadily move thermal energy to the engine boundary and dump it, as heat, to surroundings. While heat leaves, all is well. But thermal energy elimination schemes do fail, whereupon the required or normal heat (dump, elimination, or expulsion) becomes less. As the system under-heats, the machine begins to retains thermal energy and engine temperatures sky-rocket. The thermodynamically ignorant see temperature go up and claim the effect to be overheating or heat added to the engine. A destroyed engine is a sadness. If more people knew just a little thermo, there would be fewer under-heating catastrophes.