I'm still a bit new to Aristotle, so this question may be imperfect:
In Meteorology, Aristotle uses friction to explain how the sun generates heat. Although it's composed of aether, and not fire, the sun moves rapidly around a sphere of fire and/or exhalation, creating friction and thereby heating the sublunary world.
However, because Aristotle believes heat is in some sense a "thing" (as one of the two contraries that makes up fire and air respectively) rather than an event (as in our modern view that heat is the vibration of particles) it seems to me that he needs an explanation for why friction, of the sun, sticks, flint, etc. generate that thing out of the fire or exhalation. Unfortunately, I've yet to come across one. My reading is still incomplete and scattered however, and neither can I claim to have understood all that I've read!
Is such an explanation anywhere, even just implicitly, in his corpus? Or alternatively (and this being Aristotle), is there a subtler reason why this question might be misconstruing him or miss the point?
EDIT: So it seems like I don't yet have a handle on the Aristotelian view of heat (see comments). I'm leaving this question open while I do more reading in case someone wants to come along and provide some much-needed clarity, but please consider it tweaked to: Does Aristotle's concept of heat differ from ours, and if so how does he relate that concept to friction?