Question

How does friction produce heat?

Answer 1

Lets take a solid as a example, now at the atomic level imagine it is made up of a huge number of balls which are then attached to their neighbors surrounding them by springs. Heat is those balls vibrating, the hotter they are the more violently they will vibrate.
Friction creates heat in the way that you are taking two solids and causing the balls that come into contact with each other to move and then pulled back into place by the springs, then what do all springs do when they snap back they vibrate.
Lets try to understand in more simple words:
The more friction there is when moving the two solids over each other the more heat will be generated.
When two surfaces comes in contact their molecular orbital get overlap and there is a change in potential energy of system as system position changes( when body move relatively) and divergence of this potential energy function gives force in perpendicular direction and this force is called friction force in tangential direction & reaction force.