Physics · Ch 8 — Heat and Thermodynamics
Meaning of Heat
Meaning of Heat
"Heat" names the energy that flows from a hotter object to a cooler one purely because of their temperature difference -- it is energy in transit, not a quantity a body possesses. The book makes this vivid with two parallel examples: just as "a lake has more rain" is wrong (rain is a process that brings water to the lake; the lake simply "has more water" afterward), "a hot cup of coffee has more heat" is equally wrong -- heating is the process that brought energy to the coffee, and once the process stops (the coffee is taken off the stove), it no longer makes sense to speak of "heat" being present at all; the coffee simply "has more internal energy" than before, and the correct everyday description is that "the coffee i …
What this figure shows. Two side-by-side sketches of the same person: in the first, the person rubs their two hands together, illustrating that the temperature rise of the hands comes purely from work (mechanical rubbing) with no heat flow involved, since both hands start at the same temperature; in the second, the person places their warmed hands on their chin, illustrating that the chin's temperature rise comes from heat flowing from the hotter hands to the cooler chin because the two are now at different temperatures and in direct contact. The figure is used to visually separate the two distinct mechanisms -- work (mechanical, temperature difference not required) versus heat (temperatur …