The microscopic origin of contact forces is diverse. Normal force is directly a result of
Pauli exclusion principle and not a true force per se: Everyday objects do not
actually touch each other; rather, contact forces are the result of the interactions of the
electrons at or near the surfaces of the objects. As for friction, it is a result of both microscopic adhesion and
chemical bond formation due to the
electromagnetic force, and of microscopic structures stressing into each other; in the latter phenomena, in order to allow motion, the microscopic structures must either slide one above the other, or must acquire enough energy to break one another. Thus the force acting against motion is a combination of the normal force and of the force required to widen microscopic cracks within matter; the latter force is again due to
electromagnetic interaction. Additionally, strain is created inside matter, and this strain is due to a combination of
electromagnetic interactions (as electrons are attracted to nuclei and repelled from each other) and of Pauli exclusion principle, the latter working similarly to the case of normal force. ==See also==