# Is friction a product of Newton's third law?

Newton's third law is defined as $F_{12} = -F_{21}$

Is friction a product of this law? For example, if I take my hand and slide it across the floor in the $+x$ direction... My hand exerts a force $F_1$ on the floor. According to Newton's third law, the floor should exert a force of $F_2$ on my hand, and $F_2 = -F_1$.

Is $F_2$ friction? Or is friction an additional force that occurs on top of $F_2$?

• Both forces are friction. The pairs of forces described by Newton III are always of the same type. – bdsl Oct 21 '15 at 12:05