TITLE: Quantum Mechanical description of friction and temperature caused by friction
QUESTION [0 upvotes]: I was watching a pop-sci video about how we never truly touch something, and we just feel the electromagnetic repulsion of atoms.
I knew that but it made me think.
If we cannot truly touch something, then what is friction?
And how -if i hold a pen really tight and move my fingers up and down fast - then both the pen and my fingers will get warm?
If these two never touch, what is generating the heat from the friction?

REPLY [2 votes]: Quantum mechanics isn't really needed to explain friction and heat. At smaller scales, friction is basically the collision between protruding edges of rough surfaces. It is because of the electromagnetic repulsion, among other things, that the objects 'collide' and don't pass through each other, even if the collisions are happening without touching. And this is why in solids the linear motion is converted into vibrational or rotational energy in the atoms or molecules through the electromagnetic repulsion, and this kinetic energy is what we perceive as heat.
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