CHAPTER XVI.
321. Why does friction produce heat?
Because all bodies contain latent heat, that is, heat that lies hid in their substance, and the rubbings of two bodies against each other draws the latent heat to the excited surfaces.
322. Why does the rubbing of two surfaces together attract latent heat to those surfaces?
Because it is a law of nature that heat shall always attend motion; and it is generally found that the intensity of heat bears a specific relation to the velocity of motion.
323. What are the sources of heat?
The rays of the sun, the currents of electricity, the action of chemicals, and the motion of substances.
Because its latent heat is partly drawn off by the surrounding air.