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This question is basically a spin off from my friend's question - "What are we basically seeing? Is it the atom or the nucleus?" (He had referred to the huge amount of empty space inside the atoms). I replied that it must be the electronic transitions between different orbitals. It gets energy from outside, it then goes in some orbit inside, but it is unstable there, so it releases energy and comes back to its original orbit. If the corresponding wavelength matches a particular colour, we detect it. (Typical explanation based on Bohr's model).
Now another question arises that what we must be touching (suppose if we touch the keyboard), because most of the space inside the atom is empty. The size of the nucleus is almost 100,000 times less than the atom. So are we touching the atoms or the nucleus? Or the lattice arrangement of atoms? What about liquids then?
Another thing I know is that frictional & other contact forces have electromagnetic origins but I don't know exactly how. Can someone please explain?